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Groups > sci.electronics.design > #747328 > unrolled thread
| Started by | john larkin <jl@glen--canyon.com> |
|---|---|
| First post | 2026-09-07 08:18 -0700 |
| Last post | 2026-09-26 10:25 -0400 |
| Articles | 20 on this page of 259 — 26 participants |
Back to article view | Back to sci.electronics.design
discharging caps john larkin <jl@glen--canyon.com> - 2026-09-07 08:18 -0700
Re: discharging caps Simon Simple <nothanks@nottoday.co.uk> - 2026-09-07 17:20 +0100
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-07 09:58 -0700
Re: discharging caps Simon Simple <nothanks@nottoday.co.uk> - 2026-09-07 19:51 +0100
Re: discharging caps legg <legg@nospam.magma.ca> - 2026-09-08 10:27 -0400
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-08 08:16 -0700
Re: discharging caps Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2026-09-08 15:44 +0000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-08 09:35 -0700
Re: discharging caps ehsjr <ehsjr@verizon.net> - 2026-09-07 12:26 -0400
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-07 10:00 -0700
Re: discharging caps liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2026-09-07 19:32 +0100
Re: discharging caps john larkin <jl@htigct.com> - 2026-09-07 15:38 -0700
Re: discharging caps Jan Panteltje <alien@comet.invalid> - 2026-09-08 07:41 +0000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-08 07:57 -0700
Re: discharging caps Jan Panteltje <alien@comet.invalid> - 2026-09-08 15:23 +0000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-08 09:38 -0700
Re: discharging caps Jan Panteltje <alien@comet.invalid> - 2026-09-09 10:33 +0000
Re: discharging caps Simon Simple <nothanks@nottoday.co.uk> - 2026-09-11 11:54 +0100
Re: discharging caps Jan Panteltje <alien@comet.invalid> - 2026-09-11 11:01 +0000
Re: discharging caps Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2026-09-11 13:59 +0000
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-08 04:28 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-07 11:59 -0700
Re: discharging caps chrisq <syseng@gfsys.co.uk> - 2026-09-07 19:33 +0100
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-07 11:52 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-08 17:35 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-08 07:43 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-09 02:03 +1000
Re: discharging caps john larkin <jl@htigct.com> - 2026-09-08 13:10 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-09 16:25 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-08 08:00 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-09 03:09 +1000
Re: discharging caps john larkin <jl@htigct.com> - 2026-09-08 12:56 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-09 16:40 +1000
Re: discharging caps piglet <erichpwagner@hotmail.com> - 2026-09-09 09:51 +0000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-09 03:44 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-09 20:57 +1000
Re: discharging caps Jeroen Belleman <jeroen@nospam.please> - 2026-09-09 14:25 +0200
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-10 00:12 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-09 07:59 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-10 02:27 +1000
Re: discharging caps john larkin <jl@htigct.com> - 2026-09-09 10:42 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-10 17:43 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-10 07:10 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-11 00:58 +1000
Re: discharging caps chrisq <syseng@gfsys.co.uk> - 2026-09-09 17:29 +0100
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-10 03:35 +1000
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-10 01:32 +1000
Re: discharging caps Jeroen Belleman <jeroen@nospam.please> - 2026-09-09 23:10 +0200
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-10 18:38 +1000
Re: discharging caps antispam@fricas.org (Waldek Hebisch) - 2026-09-13 00:27 +0000
Re: discharging caps Lane W <cactus_DAC@yahoo.com> - 2026-09-12 18:38 -0600
Re: discharging caps antispam@fricas.org (Waldek Hebisch) - 2026-09-13 03:11 +0000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-13 07:50 -0700
Re: discharging caps Lane W <cactus_DAC@yahoo.com> - 2026-09-13 09:14 -0600
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-14 02:18 +1000
Re: discharging caps Lane W <cactus_DAC@yahoo.com> - 2026-09-13 10:28 -0600
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-14 01:28 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-13 12:03 -0700
Re: discharging caps Simon Simple <nothanks@nottoday.co.uk> - 2026-09-13 23:54 +0100
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-13 17:12 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-14 16:05 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-14 08:21 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-15 18:28 +1000
Re: discharging caps john larkin <jl@htigct.com> - 2026-09-15 10:23 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-16 18:39 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-16 03:21 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-16 21:16 +1000
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-14 15:59 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-14 08:22 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-15 18:31 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-12 17:59 -0700
Re: discharging caps wmartin <wwm@wwmartin.net> - 2026-09-12 21:21 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-13 16:27 +1000
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-13 16:24 +1000
Re: discharging caps antispam@fricas.org (Waldek Hebisch) - 2026-09-13 13:36 +0000
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-14 02:05 +1000
Re: discharging caps John R Walliker <jrwalliker@gmail.com> - 2026-09-13 19:40 +0100
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-13 12:08 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-14 16:18 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-14 08:24 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-15 18:36 +1000
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-14 16:11 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-14 08:56 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-15 18:50 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-10 07:17 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-11 01:02 +1000
Re: discharging caps chrisq <syseng@gfsys.co.uk> - 2026-09-08 11:19 +0100
Re: discharging caps chrisq <syseng@gfsys.co.uk> - 2026-09-08 11:33 +0100
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-08 07:23 -0700
Re: discharging caps chrisq <syseng@gfsys.co.uk> - 2026-09-08 16:28 +0100
Re: discharging caps chrisq <syseng@gfsys.co.uk> - 2026-09-08 21:13 +0100
Re: discharging caps john larkin <jl@htigct.com> - 2026-09-08 16:06 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-09 02:10 +1000
Re: discharging caps john larkin <jl@htigct.com> - 2026-09-08 12:59 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-09 16:45 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-09 03:22 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-09 21:07 +1000
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-09 02:10 +1000
Re: discharging caps Buzz McCool <buzz_mccool@yahoo.com> - 2026-09-14 09:44 -0700
Re: discharging caps john larkin <jl@htigct.com> - 2026-09-14 10:15 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-11 16:23 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-11 07:45 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-12 01:59 +1000
Re: discharging caps Cydrome Leader <presence@MUNGEpanix.com> - 2026-09-17 07:19 +0000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-17 07:46 -0700
Re: discharging caps Cydrome Leader <presence@MUNGEpanix.com> - 2026-09-18 04:54 +0000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-18 07:57 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-18 15:45 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-18 08:02 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-19 16:40 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-19 08:48 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-20 16:30 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-20 02:17 -0700
Re: discharging caps Simon Simple <nothanks@nottoday.co.uk> - 2026-09-20 12:30 +0100
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-21 00:52 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-20 08:46 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-21 17:41 +1000
Re: discharging caps Jan Panteltje <alien@comet.invalid> - 2026-09-08 07:46 +0000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-08 07:26 -0700
Re: discharging caps Lasse Langwadt <llc@fonz.dk> - 2026-09-07 21:18 +0200
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-07 12:36 -0700
Re: discharging caps liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2026-09-07 22:26 +0100
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-07 15:14 -0700
Re: discharging caps "Edward Rawde" <invalid@invalid.invalid> - 2026-09-07 20:06 -0400
Re: discharging caps Don Y <blockedofcourse@foo.invalid> - 2026-09-07 19:30 -0700
Re: discharging caps "Edward Rawde" <invalid@invalid.invalid> - 2026-09-07 23:40 -0400
Re: discharging caps Don Y <blockedofcourse@foo.invalid> - 2026-09-07 22:04 -0700
Re: discharging caps liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2026-09-08 08:45 +0100
Re: discharging caps John R Walliker <jrwalliker@gmail.com> - 2026-09-08 11:59 +0100
Re: discharging caps liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2026-09-08 12:30 +0100
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-08 07:34 -0700
Re: discharging caps ehsjr <ehsjr@verizon.net> - 2026-09-08 12:55 -0400
Re: discharging caps liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2026-09-13 08:15 +0100
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-13 07:41 -0700
Re: discharging caps liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2026-09-13 17:45 +0100
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-14 03:53 +1000
Re: discharging caps John R Walliker <jrwalliker@gmail.com> - 2026-09-13 19:28 +0100
Re: discharging caps ehsjr <ehsjr@verizon.net> - 2026-09-13 17:16 -0400
Re: discharging caps legg <legg@nospam.magma.ca> - 2026-09-14 10:20 -0400
Re: discharging caps liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2026-09-14 15:41 +0100
Re: discharging caps Carl <carl.ijamesXX@YYverizon.net> - 2026-09-07 21:10 -0400
Re: discharging caps legg <legg@nospam.magma.ca> - 2026-09-08 10:37 -0400
Re: discharging caps Jeremiah Jones <jj@j.j> - 2026-09-08 22:14 -0700
Re: discharging caps someone <2a59d59e3809f827ce709d3815e3950eef4a6a93af5557a93a7fdfba71460843@example.com> - 2026-09-09 17:45 +0000
Re: discharging caps john larkin <jl@htigct.com> - 2026-09-09 11:40 -0700
Re: discharging caps Simon Simple <nothanks@nottoday.co.uk> - 2026-09-10 09:55 +0100
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-10 07:20 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-11 16:32 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-11 07:46 -0700
Re: discharging caps Simon Simple <nothanks@nottoday.co.uk> - 2026-09-11 17:08 +0100
Re: discharging caps john larkin <jl@htigct.com> - 2026-09-11 14:28 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-12 16:24 +1000
Re: discharging caps John R Walliker <jrwalliker@gmail.com> - 2026-09-12 10:49 +0100
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-13 01:09 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-12 07:54 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-13 01:20 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-12 09:12 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-13 02:53 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-12 12:43 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-13 16:37 +1000
Re: discharging caps Joerg <news@analogconsultants.com> - 2026-09-09 15:15 -0700
Re: discharging caps liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2026-09-10 12:25 +0100
Re: discharging caps Simon Simple <nothanks@nottoday.co.uk> - 2026-09-10 13:09 +0100
Re: discharging caps John R Walliker <jrwalliker@gmail.com> - 2026-09-10 14:10 +0100
Re: discharging caps Joerg <news@analogconsultants.com> - 2026-09-10 11:05 -0700
Re: discharging caps Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2026-09-10 19:12 +0000
Re: discharging caps legg <legg@nospam.magma.ca> - 2026-09-13 14:52 -0400
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-13 12:17 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-14 16:25 +1000
Re: discharging caps legg <legg@nospam.magma.ca> - 2026-09-14 10:15 -0400
Re: discharging caps "Edward Rawde" <invalid@invalid.invalid> - 2026-09-17 19:53 -0400
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-17 19:15 -0700
Re: discharging caps "Edward Rawde" <invalid@invalid.invalid> - 2026-09-17 23:50 -0400
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-18 15:58 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-18 07:26 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-19 16:26 +1000
Re: discharging caps legg <legg@nospam.magma.ca> - 2026-09-20 11:25 -0400
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-20 08:42 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-21 17:54 +1000
Re: discharging caps john larkin <jl@htigct.com> - 2026-09-21 10:09 -0700
Re: discharging caps legg <legg@nospam.magma.ca> - 2026-09-21 08:59 -0400
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-21 08:02 -0700
Re: discharging caps legg <legg@nospam.magma.ca> - 2026-09-21 13:00 -0400
Re: discharging caps john larkin <jl@htigct.com> - 2026-09-21 10:12 -0700
Re: discharging caps legg <legg@nospam.magma.ca> - 2026-09-22 10:12 -0400
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-22 08:25 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-23 03:55 +1000
Re: discharging caps john larkin <jl@htigct.com> - 2026-09-22 17:36 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-23 16:18 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-23 09:05 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-24 16:36 +1000
Re: discharging caps legg <legg@nospam.magma.ca> - 2026-09-24 08:11 -0400
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-24 07:26 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-25 00:52 +1000
Re: discharging caps ehsjr <ehsjr@verizon.net> - 2026-09-24 18:40 -0400
Re: discharging caps john larkin <jl@htigct.com> - 2026-09-24 16:22 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-25 16:50 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-25 07:26 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-26 01:32 +1000
Re: discharging caps antispam@fricas.org (Waldek Hebisch) - 2026-09-26 03:12 +0000
Re: discharging caps "Edward Rawde" <invalid@invalid.invalid> - 2026-09-26 00:38 -0400
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-26 07:08 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-27 01:07 +1000
Re: discharging caps JM <sunaecoNoChoppedPork@gmail.com> - 2026-09-26 15:49 +0100
Re: discharging caps john larkin <jl@htigct.com> - 2026-09-28 10:11 -0700
Re: discharging caps legg <legg@nospam.magma.ca> - 2026-09-23 09:24 -0400
Re: discharging caps Jan Panteltje <alien@comet.invalid> - 2026-09-21 17:01 +0000
Re: discharging caps legg <legg@nospam.magma.ca> - 2026-09-20 11:44 -0400
Re: discharging caps liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2026-09-23 21:42 +0100
Re: discharging caps Lane W <cactus_DAC@yahoo.com> - 2026-09-23 14:44 -0600
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-23 17:51 -0700
Re: discharging caps liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2026-09-24 10:07 +0100
Re: discharging caps Simon Simple <nothanks@nottoday.co.uk> - 2026-09-24 12:01 +0100
Re: discharging caps liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2026-09-24 13:59 +0100
Re: discharging caps john larkin <jl@htigct.com> - 2026-09-23 14:16 -0700
Re: discharging caps liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2026-09-24 10:07 +0100
Re: discharging caps john larkin <jl@htigct.com> - 2026-09-24 11:51 -0700
Re: discharging caps legg <legg@nospam.magma.ca> - 2026-09-24 07:58 -0400
Re: discharging caps legg <legg@nospam.magma.ca> - 2026-09-24 07:54 -0400
Re: discharging caps liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2026-09-24 13:59 +0100
Re: discharging caps legg <legg@nospam.magma.ca> - 2026-09-24 17:56 -0400
Re: discharging caps john larkin <jl@htigct.com> - 2026-09-24 16:27 -0700
Re: discharging caps liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2026-09-25 09:22 +0100
Re: discharging caps john larkin <jl@htigct.com> - 2026-09-24 11:55 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-25 17:09 +1000
Re: discharging caps Jeroen Belleman <jeroen@nospam.please> - 2026-09-25 09:38 +0200
Re: discharging caps John R Walliker <jrwalliker@gmail.com> - 2026-09-25 10:59 +0100
Re: discharging caps Jeroen Belleman <jeroen@nospam.please> - 2026-09-25 12:28 +0200
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-25 22:42 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-25 07:38 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-26 01:11 +1000
Re: discharging caps Jeroen Belleman <jeroen@nospam.please> - 2026-09-25 19:59 +0200
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-26 15:56 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-26 09:24 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-27 16:22 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-27 03:20 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-27 20:55 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-27 07:59 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-28 12:35 +1000
Re: discharging caps john larkin <jl@htigct.com> - 2026-09-28 10:15 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-29 17:22 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-26 07:20 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-27 01:26 +1000
Re: discharging caps Jeroen Belleman <jeroen@nospam.please> - 2026-09-26 22:58 +0200
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-26 16:20 -0700
Re: discharging caps Jan Panteltje <alien@comet.invalid> - 2026-09-27 07:39 +0000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-27 03:29 -0700
Re: discharging caps Jan Panteltje <alien@comet.invalid> - 2026-09-27 13:50 +0000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-27 08:04 -0700
Re: discharging caps Jan Panteltje <alien@comet.invalid> - 2026-09-27 15:16 +0000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-27 08:29 -0700
Re: discharging caps Jan Panteltje <alien@comet.invalid> - 2026-09-28 06:38 +0000
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-28 17:34 +1000
Re: discharging caps john larkin <jl@htigct.com> - 2026-09-28 10:17 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-29 17:09 +1000
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-28 12:54 +1000
Re: discharging caps john larkin <jl@glen--canyon.com> - 2026-09-27 20:14 -0700
Re: discharging caps Bill Sloman <bill.sloman@ieee.org> - 2026-09-28 16:58 +1000
Re: discharging caps legg <legg@nospam.magma.ca> - 2026-09-26 10:25 -0400
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| From | Bill Sloman <bill.sloman@ieee.org> |
|---|---|
| Date | 2026-09-14 16:05 +1000 |
| Message-ID | <11882rn$18ct6$3@dont-email.me> |
| In reply to | #747702 |
On 14/09/2026 10:12 am, john larkin wrote: > On Sun, 13 Sep 2026 23:54:47 +0100, Simon Simple > <nothanks@nottoday.co.uk> wrote: > >> On 13/09/2026 20:03, john larkin wrote: >> >> <xxxx>> >>> 130 KG is a lot of stuff. >> >> 130 kelvin gauss? > > Don't be silly. The measurement is obviously in kangaroo gibongs. Kangaroo's I've seen. "Gibongs" apears to be a nonsense word. My guess is that John Larin meant kilograms, for which the usual abbreviation is kgm, not KG. >>> Engineers benefit from quickly discounting designs that are orders of >>> magnitude away from being sensible. Lazy engineers save their brains from excessive effort by telling themselves that. It isn't always true, but john Larkin lies to himself about that too. -- Bill Sloman, Sydney
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| From | john larkin <jl@glen--canyon.com> |
|---|---|
| Date | 2026-09-14 08:21 -0700 |
| Message-ID | <743galpkcbop198kgoftoa132srh36f40r@4ax.com> |
| In reply to | #747708 |
On Mon, 14 Sep 2026 16:05:43 +1000, Bill Sloman <bill.sloman@ieee.org> wrote: >On 14/09/2026 10:12 am, john larkin wrote: >> On Sun, 13 Sep 2026 23:54:47 +0100, Simon Simple >> <nothanks@nottoday.co.uk> wrote: >> >>> On 13/09/2026 20:03, john larkin wrote: >>> >>> <xxxx>> >>>> 130 KG is a lot of stuff. >>> >>> 130 kelvin gauss? >> >> Don't be silly. The measurement is obviously in kangaroo gibongs. >Kangaroo's I've seen. "Gibongs" apears to be a nonsense word. Nobody could ever accuse you of attempting humor. > >My guess is that John Larin meant kilograms, for which the usual >abbreviation is kgm, not KG. gm? What's a gm? Transconductance? > >>>> Engineers benefit from quickly discounting designs that are orders of >>>> magnitude away from being sensible. > >Lazy engineers save their brains from excessive effort by telling >themselves that. It isn't always true, but john Larkin lies to himself >about that too. 130 kilograms of inductor is clearly absurd by about 4 orders of magnitude. A few seconds of mental calculation dismisses the inductor idea. [1] Besides the quantitative absurdity, depletion fets are smaller and cheaper than inductors, and surface mount. DN2530 costs us 43 cents. Design a better discharge circuit, with values, and we can discuss it. [1] I'm sort of known for doing math like this standing up at a whiteboard. There are actually tricks, known as "lightning empiricism" Jim Wiliams' 1991 book has a section on that. John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
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| From | Bill Sloman <bill.sloman@ieee.org> |
|---|---|
| Date | 2026-09-15 18:28 +1000 |
| Message-ID | <118avjr$281am$4@dont-email.me> |
| In reply to | #747729 |
On 15/09/2026 1:21 am, john larkin wrote: > On Mon, 14 Sep 2026 16:05:43 +1000, Bill Sloman <bill.sloman@ieee.org> > wrote: > >> On 14/09/2026 10:12 am, john larkin wrote: >>> On Sun, 13 Sep 2026 23:54:47 +0100, Simon Simple >>> <nothanks@nottoday.co.uk> wrote: >>> >>>> On 13/09/2026 20:03, john larkin wrote: >>>> >>>> <xxxx>> >>>>> 130 KG is a lot of stuff. >>>> >>>> 130 kelvin gauss? >>> >>> Don't be silly. The measurement is obviously in kangaroo gibongs. >> Kangaroo's I've seen. "Gibongs" apears to be a nonsense word. > > Nobody could ever accuse you of attempting humor. Not that you've noticed. If you were trying to be funny, you didn't make it. >> My guess is that John Larin meant kilograms, for which the usual >> abbreviation is kgm, not KG. > > gm? What's a gm? Transconductance? American physics courses don't seem to have been big on System International (SI) units when young Larkin was young and somewhat susceptible to education. >>>>> Engineers benefit from quickly discounting designs that are orders of >>>>> magnitude away from being sensible. >> >> Lazy engineers save their brains from excessive effort by telling >> themselves that. It isn't always true, but john Larkin lies to himself >> about that too. > > 130 kilograms of inductor is clearly absurd by about 4 orders of > magnitude. A few seconds of mental calculation dismisses the inductor > idea. [1] > > Besides the quantitative absurdity, depletion fets are smaller and > cheaper than inductors, and surface mount. DN2530 costs us 43 cents. https://www.mouser.com/datasheet/2/391/DN2530-36932.pdf?srsltid=AfmBOorXOdCkWEQBmjqXp5tGJIUvVC5VAQqugUbHjdpvBszaeReYJDUP It's tiny. You really don't want it to carry more than 300mA (even briefly) and you need to bias the gate about 10V below the source to keep it off. It may be a practicable solution, but it won't be a simple one. > Design a better discharge circuit, with values, and we can discuss it. > > [1] I'm sort of known for doing math like this standing up at a > whiteboard. There are actually tricks, known as "lightning empiricism" > > Jim Wiliams' 1991 book has a section on that. John Larkin is better known for his skills in self-congratulation. -- Bill Sloman, Sydney
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| From | john larkin <jl@htigct.com> |
|---|---|
| Date | 2026-09-15 10:23 -0700 |
| Message-ID | <c3viallh163kl3qkef3b4dfcq7rs4vfs2g@4ax.com> |
| In reply to | #747762 |
On Tue, 15 Sep 2026 18:28:40 +1000, Bill Sloman <bill.sloman@ieee.org> wrote: >On 15/09/2026 1:21 am, john larkin wrote: >> On Mon, 14 Sep 2026 16:05:43 +1000, Bill Sloman <bill.sloman@ieee.org> >> wrote: >> >>> On 14/09/2026 10:12 am, john larkin wrote: >>>> On Sun, 13 Sep 2026 23:54:47 +0100, Simon Simple >>>> <nothanks@nottoday.co.uk> wrote: >>>> >>>>> On 13/09/2026 20:03, john larkin wrote: >>>>> >>>>> <xxxx>> >>>>>> 130 KG is a lot of stuff. >>>>> >>>>> 130 kelvin gauss? >>>> >>>> Don't be silly. The measurement is obviously in kangaroo gibongs. >>> Kangaroo's I've seen. "Gibongs" apears to be a nonsense word. >> >> Nobody could ever accuse you of attempting humor. > >Not that you've noticed. If you were trying to be funny, you didn't make it. > >>> My guess is that John Larin meant kilograms, for which the usual >>> abbreviation is kgm, not KG. >> >> gm? What's a gm? Transconductance? > >American physics courses don't seem to have been big on System >International (SI) units when young Larkin was young and somewhat >susceptible to education. https://en.wikipedia.org/wiki/Gram The unit is g not gm. > >>>>>> Engineers benefit from quickly discounting designs that are orders of >>>>>> magnitude away from being sensible. >>> >>> Lazy engineers save their brains from excessive effort by telling >>> themselves that. It isn't always true, but john Larkin lies to himself >>> about that too. >> >> 130 kilograms of inductor is clearly absurd by about 4 orders of >> magnitude. A few seconds of mental calculation dismisses the inductor >> idea. [1] >> >> Besides the quantitative absurdity, depletion fets are smaller and >> cheaper than inductors, and surface mount. DN2530 costs us 43 cents. > >https://www.mouser.com/datasheet/2/391/DN2530-36932.pdf?srsltid=AfmBOorXOdCkWEQBmjqXp5tGJIUvVC5VAQqugUbHjdpvBszaeReYJDUP > >It's tiny. You really don't want it to carry more than 300mA (even >briefly) and you need to bias the gate about 10V below the source to >keep it off. It may be a practicable solution, but it won't be a simple one. I posted my discharge circuit. It's simple. And the DN2530 pinches off around -2 volts. When you were in school, didn't they teach you to check your work? > >> Design a better discharge circuit, with values, and we can discuss it. >> >> [1] I'm sort of known for doing math like this standing up at a >> whiteboard. There are actually tricks, known as "lightning empiricism" > > >> Jim Wiliams' 1991 book has a section on that. > >John Larkin is better known for his skills in self-congratulation. No, I let other people do that.
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| From | Bill Sloman <bill.sloman@ieee.org> |
|---|---|
| Date | 2026-09-16 18:39 +1000 |
| Message-ID | <118dkk7$36kea$4@dont-email.me> |
| In reply to | #747778 |
On 16/09/2026 3:23 am, john larkin wrote: > On Tue, 15 Sep 2026 18:28:40 +1000, Bill Sloman <bill.sloman@ieee.org> > wrote: > >> On 15/09/2026 1:21 am, john larkin wrote: >>> On Mon, 14 Sep 2026 16:05:43 +1000, Bill Sloman <bill.sloman@ieee.org> >>> wrote: >>> >>>> On 14/09/2026 10:12 am, john larkin wrote: >>>>> On Sun, 13 Sep 2026 23:54:47 +0100, Simon Simple >>>>> <nothanks@nottoday.co.uk> wrote: >>>>> >>>>>> On 13/09/2026 20:03, john larkin wrote: >>>>>> >>>>>> <xxxx>> >>>>>>> 130 KG is a lot of stuff. >>>>>> >>>>>> 130 kelvin gauss? >>>>> >>>>> Don't be silly. The measurement is obviously in kangaroo gibongs. >>>> Kangaroo's I've seen. "Gibongs" apears to be a nonsense word. >>> >>> Nobody could ever accuse you of attempting humor. >> >> Not that you've noticed. If you were trying to be funny, you didn't make it. >> >>>> My guess is that John Larin meant kilograms, for which the usual >>>> abbreviation is kgm, not KG. >>> >>> gm? What's a gm? Transconductance? >> >> American physics courses don't seem to have been big on System >> International (SI) units when young Larkin was young and somewhat >> susceptible to education. > > https://en.wikipedia.org/wiki/Gram > > The unit is g not gm. > >> >>>>>>> Engineers benefit from quickly discounting designs that are orders of >>>>>>> magnitude away from being sensible. >>>> >>>> Lazy engineers save their brains from excessive effort by telling >>>> themselves that. It isn't always true, but john Larkin lies to himself >>>> about that too. >>> >>> 130 kilograms of inductor is clearly absurd by about 4 orders of >>> magnitude. A few seconds of mental calculation dismisses the inductor >>> idea. [1] >>> >>> Besides the quantitative absurdity, depletion fets are smaller and >>> cheaper than inductors, and surface mount. DN2530 costs us 43 cents. >> >> https://www.mouser.com/datasheet/2/391/DN2530-36932.pdf?srsltid=AfmBOorXOdCkWEQBmjqXp5tGJIUvVC5VAQqugUbHjdpvBszaeReYJDUP >> >> It's tiny. You really don't want it to carry more than 300mA (even >> briefly) and you need to bias the gate about 10V below the source to >> keep it off. It may be a practicable solution, but it won't be a simple one. > > I posted my discharge circuit. It's simple. And the DN2530 pinches off > around -2 volts. > > When you were in school, didn't they teach you to check your work? You need more than -2V for a proper pinch-off. I check my work to my pown standards, not yours. >>> Design a better discharge circuit, with values, and we can discuss it. >>> >>> [1] I'm sort of known for doing math like this standing up at a >>> whiteboard. There are actually tricks, known as "lightning empiricism" >>> >>> Jim Wiliams' 1991 book has a section on that. >> >> John Larkin is better known for his skills in self-congratulation. > > No, I let other people do that. But you do make it clear that if they don't do it they will end up being accused of being negative and insulting. And "I'm sort of known for doing math like this standing up at a whiteboard" does look remarkably like self-congratulation. -- Bill Sloman, Sydney
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| From | john larkin <jl@glen--canyon.com> |
|---|---|
| Date | 2026-09-16 03:21 -0700 |
| Message-ID | <eiqkal111otd7c5e6jf6vgkkn5tq6str5l@4ax.com> |
| In reply to | #747793 |
On Wed, 16 Sep 2026 18:39:28 +1000, Bill Sloman <bill.sloman@ieee.org> wrote: >On 16/09/2026 3:23 am, john larkin wrote: >> On Tue, 15 Sep 2026 18:28:40 +1000, Bill Sloman <bill.sloman@ieee.org> >> wrote: >> >>> On 15/09/2026 1:21 am, john larkin wrote: >>>> On Mon, 14 Sep 2026 16:05:43 +1000, Bill Sloman <bill.sloman@ieee.org> >>>> wrote: >>>> >>>>> On 14/09/2026 10:12 am, john larkin wrote: >>>>>> On Sun, 13 Sep 2026 23:54:47 +0100, Simon Simple >>>>>> <nothanks@nottoday.co.uk> wrote: >>>>>> >>>>>>> On 13/09/2026 20:03, john larkin wrote: >>>>>>> >>>>>>> <xxxx>> >>>>>>>> 130 KG is a lot of stuff. >>>>>>> >>>>>>> 130 kelvin gauss? >>>>>> >>>>>> Don't be silly. The measurement is obviously in kangaroo gibongs. >>>>> Kangaroo's I've seen. "Gibongs" apears to be a nonsense word. >>>> >>>> Nobody could ever accuse you of attempting humor. >>> >>> Not that you've noticed. If you were trying to be funny, you didn't make it. >>> >>>>> My guess is that John Larin meant kilograms, for which the usual >>>>> abbreviation is kgm, not KG. >>>> >>>> gm? What's a gm? Transconductance? >>> >>> American physics courses don't seem to have been big on System >>> International (SI) units when young Larkin was young and somewhat >>> susceptible to education. >> >> https://en.wikipedia.org/wiki/Gram >> >> The unit is g not gm. >> >>> >>>>>>>> Engineers benefit from quickly discounting designs that are orders of >>>>>>>> magnitude away from being sensible. >>>>> >>>>> Lazy engineers save their brains from excessive effort by telling >>>>> themselves that. It isn't always true, but john Larkin lies to himself >>>>> about that too. >>>> >>>> 130 kilograms of inductor is clearly absurd by about 4 orders of >>>> magnitude. A few seconds of mental calculation dismisses the inductor >>>> idea. [1] >>>> >>>> Besides the quantitative absurdity, depletion fets are smaller and >>>> cheaper than inductors, and surface mount. DN2530 costs us 43 cents. >>> >>> https://www.mouser.com/datasheet/2/391/DN2530-36932.pdf?srsltid=AfmBOorXOdCkWEQBmjqXp5tGJIUvVC5VAQqugUbHjdpvBszaeReYJDUP >>> >>> It's tiny. You really don't want it to carry more than 300mA (even >>> briefly) and you need to bias the gate about 10V below the source to >>> keep it off. It may be a practicable solution, but it won't be a simple one. >> >> I posted my discharge circuit. It's simple. And the DN2530 pinches off >> around -2 volts. >> >> When you were in school, didn't they teach you to check your work? > >You need more than -2V for a proper pinch-off. I check my work to my >pown standards, not yours. And your spelling, too. > >>>> Design a better discharge circuit, with values, and we can discuss it. >>>> >>>> [1] I'm sort of known for doing math like this standing up at a >>>> whiteboard. There are actually tricks, known as "lightning empiricism" >>>> >>>> Jim Wiliams' 1991 book has a section on that. >>> >>> John Larkin is better known for his skills in self-congratulation. >> >> No, I let other people do that. > >But you do make it clear that if they don't do it they will end up being >accused of being negative and insulting. Most of your posts are coarse insults. > >And "I'm sort of known for doing math like this standing up at a >whiteboard" does look remarkably like self-congratulation. As noted, "lightning empiricism" is handy, and not especially difficult. I was recently sitting in on a class at CCSF and the prof was lecturing about a circuit. He said "the current is 6 divided by 0.05. Does anbody know what that is? Nobody did, so I said "120" and he said "thank you". None of the maybe 30 kids in the room could do the math in their heads. It's two simple steps. John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
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| From | Bill Sloman <bill.sloman@ieee.org> |
|---|---|
| Date | 2026-09-16 21:16 +1000 |
| Message-ID | <118dtqq$3apsl$2@dont-email.me> |
| In reply to | #747795 |
On 16/09/2026 8:21 pm, john larkin wrote: > On Wed, 16 Sep 2026 18:39:28 +1000, Bill Sloman <bill.sloman@ieee.org> > wrote: > >> On 16/09/2026 3:23 am, john larkin wrote: >>> On Tue, 15 Sep 2026 18:28:40 +1000, Bill Sloman <bill.sloman@ieee.org> >>> wrote: >>> >>>> On 15/09/2026 1:21 am, john larkin wrote: >>>>> On Mon, 14 Sep 2026 16:05:43 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>> wrote: >>>>> >>>>>> On 14/09/2026 10:12 am, john larkin wrote: >>>>>>> On Sun, 13 Sep 2026 23:54:47 +0100, Simon Simple >>>>>>> <nothanks@nottoday.co.uk> wrote: >>>>>>> >>>>>>>> On 13/09/2026 20:03, john larkin wrote: >>>>>>>> >>>>>>>> <xxxx>> >>>>>>>>> 130 KG is a lot of stuff. >>>>>>>> >>>>>>>> 130 kelvin gauss? >>>>>>> >>>>>>> Don't be silly. The measurement is obviously in kangaroo gibongs. >>>>>> Kangaroo's I've seen. "Gibongs" apears to be a nonsense word. >>>>> >>>>> Nobody could ever accuse you of attempting humor. >>>> >>>> Not that you've noticed. If you were trying to be funny, you didn't make it. >>>> >>>>>> My guess is that John Larin meant kilograms, for which the usual >>>>>> abbreviation is kgm, not KG. >>>>> >>>>> gm? What's a gm? Transconductance? >>>> >>>> American physics courses don't seem to have been big on System >>>> International (SI) units when young Larkin was young and somewhat >>>> susceptible to education. >>> >>> https://en.wikipedia.org/wiki/Gram >>> >>> The unit is g not gm. >>> >>>> >>>>>>>>> Engineers benefit from quickly discounting designs that are orders of >>>>>>>>> magnitude away from being sensible. >>>>>> >>>>>> Lazy engineers save their brains from excessive effort by telling >>>>>> themselves that. It isn't always true, but john Larkin lies to himself >>>>>> about that too. >>>>> >>>>> 130 kilograms of inductor is clearly absurd by about 4 orders of >>>>> magnitude. A few seconds of mental calculation dismisses the inductor >>>>> idea. [1] >>>>> >>>>> Besides the quantitative absurdity, depletion fets are smaller and >>>>> cheaper than inductors, and surface mount. DN2530 costs us 43 cents. >>>> >>>> https://www.mouser.com/datasheet/2/391/DN2530-36932.pdf?srsltid=AfmBOorXOdCkWEQBmjqXp5tGJIUvVC5VAQqugUbHjdpvBszaeReYJDUP >>>> >>>> It's tiny. You really don't want it to carry more than 300mA (even >>>> briefly) and you need to bias the gate about 10V below the source to >>>> keep it off. It may be a practicable solution, but it won't be a simple one. >>> >>> I posted my discharge circuit. It's simple. And the DN2530 pinches off >>> around -2 volts. >>> >>> When you were in school, didn't they teach you to check your work? >> >> You need more than -2V for a proper pinch-off. I check my work to my >> pown standards, not yours. > > And your spelling, too. > >> >>>>> Design a better discharge circuit, with values, and we can discuss it. >>>>> >>>>> [1] I'm sort of known for doing math like this standing up at a >>>>> whiteboard. There are actually tricks, known as "lightning empiricism" >>>>> >>>>> Jim Wiliams' 1991 book has a section on that. >>>> >>>> John Larkin is better known for his skills in self-congratulation. >>> >>> No, I let other people do that. >> >> But you do make it clear that if they don't do it they will end up being >> accused of being negative and insulting. > > Most of your posts are coarse insults. Examples? They don't flatter you as fulsomely as you'd like, but the insults are mild and fairly refined (like this one). >> And "I'm sort of known for doing math like this standing up at a >> whiteboard" does look remarkably like self-congratulation. > > As noted, "lightning empiricism" is handy, and not especially > difficult. > > I was recently sitting in on a class at CCSF and the prof was > lecturing about a circuit. He said "the current is 6 divided by 0.05. > Does anbody know what that is? Nobody did, so I said "120" and he said > "thank you". None of the maybe 30 kids in the room could do the math > in their heads. It's two simple steps. But no undergraduate wants to fall flat on their faces in front of a professor. And most of them know enough about professors to want to avoid any trap he might have set. -- Bill Sloman, Sydney
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| From | Bill Sloman <bill.sloman@ieee.org> |
|---|---|
| Date | 2026-09-14 15:59 +1000 |
| Message-ID | <11882gr$18ct6$2@dont-email.me> |
| In reply to | #747685 |
On 14/09/2026 5:03 am, john larkin wrote: > On Mon, 14 Sep 2026 01:28:04 +1000, Bill Sloman <bill.sloman@ieee.org> > wrote: > >> On 14/09/2026 12:50 am, john larkin wrote: >>> On Sun, 13 Sep 2026 03:11:25 -0000 (UTC), antispam@fricas.org (Waldek >>> Hebisch) wrote: >>> >>>> Lane W <cactus_DAC@yahoo.com> wrote: >>>>> Waldek Hebisch wrote: >>>>>> Bill Sloman <bill.sloman@ieee.org> wrote: >>>>>>> >>>>>>> >>>>>>> On 10/09/2026 7:10 am, Jeroen Belleman wrote: >>>>>>>> On 9/9/26 17:32, Bill Sloman wrote: >>>>>>>>> On 9/09/2026 10:25 pm, Jeroen Belleman wrote: >>>>>>>>>> On 9/9/26 12:44, john larkin wrote: >>>>>>>>>>> On Wed, 9 Sep 2026 09:51:57 -0000 (UTC), piglet >>>>>>>>>>> <erichpwagner@hotmail.com> wrote: >>>>>>>>>>> >>>>>>>>>>>> Bill Sloman <bill.sloman@ieee.org> wrote: >>>>>>>>>>>>> On 9/09/2026 5:56 am, john larkin wrote: >>>>>>>>>>>>>> On Wed, 9 Sep 2026 03:09:41 +1000, Bill Sloman >>>>>>>>>>>>>> <bill.sloman@ieee.org> >>>>>>>>>>>>>> wrote: >>>>>>>>>>>>>> >>>>>>>>>>>>>>> On 9/09/2026 1:00 am, john larkin wrote: >>>>>>>>>>>>>>>> On Tue, 8 Sep 2026 17:35:24 +1000, Bill Sloman >>>>>>>>>>>>>>>> <bill.sloman@ieee.org> >>>>>>>>>>>>>>>> wrote: >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> On 8/09/2026 4:52 am, john larkin wrote: >>>>>>>>>>>>>>>>>> On Mon, 7 Sep 2026 19:33:35 +0100, chrisq >>>>>>>>>>>>>>>>>> <syseng@gfsys.co.uk> wrote: >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> On 9/7/26 16:18, john larkin wrote: >>>>>>>>>>>>>>>>>>>> Suppose we have a box with some big caps inside, for >>>>>>>>>>>>>>>>>>>> example 0.2 >>>>>>>>>>>>>>>>>>>> farads that run at about 200 volts. When AC power is off, >>>>>>>>>>>>>>>>>>>> we want to >>>>>>>>>>>>>>>>>>>> discharge them for several reasons. >>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>> Putting, say, a 1K resistor across them dissipates 40 watts >>>>>>>>>>>>>>>>>>>> and has a >>>>>>>>>>>>>>>>>>>> 200 second time constant. It will take many tau before the >>>>>>>>>>>>>>>>>>>> voltage >>>>>>>>>>>>>>>>>>>> gets low enough for people to poke around inside. >>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>> The ideal discharger would be a constant-current or even >>>>>>>>>>>>>>>>>>>> better a >>>>>>>>>>>>>>>>>>>> constant-power load, all the way down to zero volts. It >>>>>>>>>>>>>>>>>>>> would be dumb, >>>>>>>>>>>>>>>>>>>> not switched by some decision circuit or anything fancy >>>>>>>>>>>>>>>>>>>> like that. >>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>> And of course we need several LEDs as warnings that the >>>>>>>>>>>>>>>>>>>> thing is hot. >>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> What sort of design needs 0.2 Farad cap, at 200 volts ?. If >>>>>>>>>>>>>>>>>>> you are >>>>>>>>>>>>>>>>>>> working at that level, put in a cheap relay and a rated >>>>>>>>>>>>>>>>>>> heatsink >>>>>>>>>>>>>>>>>>> wirewound resistor to dump the energy, when the power goes off. >>>>>>>>>>>>>>>>>>> Cheap, and lossless as well. Motor drive inverters often have >>>>>>>>>>>>>>>>>>> big resistors to brake the motor. >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>> John Larkin >>>>>>>>>>>>>>>>>>>> Highland Tech Glen Canyon Design Center >>>>>>>>>>>>>>>>>>>> Lunatic Fringe Electronics >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> It's a 1500 amp laser driver. >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> The input to our box is DC, from an external power supply. >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> I do want a circuit that's foolproof, that always discharges >>>>>>>>>>>>>>>>>> the caps >>>>>>>>>>>>>>>>>> but doen't often go up in flames. >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> A resistor makes an exponential decay which could be a very >>>>>>>>>>>>>>>>>> long time >>>>>>>>>>>>>>>>>> to get down to safe levels. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> But a resistor plus an inductor could give a critically damped >>>>>>>>>>>>>>>>> decay, >>>>>>>>>>>>>>>>> which would be quite a bit faster. I don't know enough about >>>>>>>>>>>>>>>>> the circuit >>>>>>>>>>>>>>>>> to be prepared to try to work out how much inductance you'd >>>>>>>>>>>>>>>>> need, and >>>>>>>>>>>>>>>>> you clearly can't be bothered. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> Won't be bothered. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> I thought the group might like a circuit design problem once >>>>>>>>>>>>>>>>>> in a >>>>>>>>>>>>>>>>>> while, a break from politics. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> But you don't do circuit design, and this sort of question >>>>>>>>>>>>>>>>> makes it >>>>>>>>>>>>>>>>> obvious why you don't. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> The inductor suggestion is hilarious. Thanks. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> It's elementary circuit theory, which you should have been >>>>>>>>>>>>>>> taught and I >>>>>>>>>>>>>>> had to read about. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> If you discharge a capacitor through a resistor, the voltage decays >>>>>>>>>>>>>>> exponentially. If you put an inductor in series with the >>>>>>>>>>>>>>> resistor the >>>>>>>>>>>>>>> voltage decay is a more complicated function of time. If you >>>>>>>>>>>>>>> chose the >>>>>>>>>>>>>>> resistance and the inductance to create a critically damped >>>>>>>>>>>>>>> circuit, the >>>>>>>>>>>>>>> voltage across the capacitor will eventually decay more rapidly >>>>>>>>>>>>>>> than >>>>>>>>>>>>>>> you'd see with just the resistor. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Try reading about Laplace transforms. That's a pretty hilarious >>>>>>>>>>>>>>> suggestion to direct at you, but you are the butt of the joke. >>>>>>>>>>>>>> >>>>>>>>>>>>>> Oh, RLC circuits are no mystery. >>>>>>>>>>>>>> >>>>>>>>>>>>>> What's funny about the suggestion is the size of the inductor it >>>>>>>>>>>>>> would >>>>>>>>>>>>>> need. >>>>>>>>>>>>> >>>>>>>>>>>>> Which you haven't worked out. I spent a few minutes last night >>>>>>>>>>>>> trying to >>>>>>>>>>>>> work out what I could buy off the shelf from element-14 (the >>>>>>>>>>>>> Australian >>>>>>>>>>>>> branch of Newark) but their web-site has turned cranky in recent >>>>>>>>>>>>> months. >>>>>>>>>>>>> >>>>>>>>>>>>> The value of the inductance isn't fixed - that and the resistor >>>>>>>>>>>>> can be >>>>>>>>>>>>> be chosen to get a critically damped LCR, and I figured that I'd >>>>>>>>>>>>> start >>>>>>>>>>>>> playing with an inductor I could buy. >>>>>>>>>>>>> >>>>>>>>>>>>> You might end up with a non-progressively wound air-cored toroid. >>>>>>>>>>>>> With a >>>>>>>>>>>>> 0.2F capacitor the parallel capacitance of the inductor isn't >>>>>>>>>>>>> going to >>>>>>>>>>>>> be an issue, and the winding resistance could be your damping >>>>>>>>>>>>> resistor. >>>>>>>>>>>>> >>>>>>>>>>>>> 4kJ is a fair bit of energy, but you can get copper quite hot >>>>>>>>>>>>> before it >>>>>>>>>>>>> explodes. It wouldn't stay hot for long. >>>>>>>>>>>>> >>>>>>>>>>>> >>>>>>>>>>>> I haven’t calculated what ballpark inductance might be required but >>>>>>>>>>>> is air >>>>>>>>>>>> core even feasible for that? >>>>>>>>>>> >>>>>>>>>>> If it were about the size of a truck maybe. >>>>>>>>>>> >>>>>>>>>>> You can estimate the inductance in your head. To discharge 0.2F in, >>>>>>>>>>> say 100 seconds, you need 500 ohms. That would of course be the tau of >>>>>>>>>>> an exponential decay. Adding an inductor would crisp that up. >>>>>>>>>>> >>>>>>>>>>> R*C = 100 seconds so we want L/R to be in that ballpark. >>>>>>>>> >>>>>>>>> 100 seconds is a lot too long from a safety point of view >>>>>>>>> >>>>>>>>>>> So L is around 50,000 H. >>>>>>>>> >>>>>>>>> If you start at the wrong end. >>>>>>>>> >>>>>>>>>>> Check Digikey for that. >>>>>>>>>> >>>>>>>>>> Critical damping happens when the expression for the impedance of >>>>>>>>>> the series RLC has two identical roots. This happens when L = R^2C/4, >>>>>>>>>> near enough, so L should be 12.5 kH. >>>>>>>>> >>>>>>>>> You can vary both L and R. A much shorter time constant means a much >>>>>>>>> smaller inductor >>>>>>>>> >>>>>>>>> I dug out my copy of Grover and thought about a 5H air-cored inductor. >>>>>>>>> >>>>>>>>> 5H - a 1 sec time constant - would be practicable - but big. You'd >>>>>>>>> need a great deal of copper wire to make it work. >>>>>>>>> >>>>>>>>> It might be worth thinking about an iron-cored inductor. We are >>>>>>>>> looking at a fairly slow event so the current induced in the iron >>>>>>>>> would be just one more dissipation mode. >>>>>>>>> >>>>>>>>> 0.5H might work. The time constant of 0.32 sec means that your 4kJ >>>>>>>>> looks like 13kW while it is dissipating, but it would be being >>>>>>>>> dissipated in what could be a fairly substantial resistor which >>>>>>>>> wouldn't warm up much and would have time to cool off. >>>>>>>>> >>>>>>>>>> With the initial voltage 200V, it will need to briefly store just >>>>>>>>>> short of 600 J. That doesn't look like a practical solution. >>>>>>>>> >>>>>>>>> Why not? Air-cored coils can store a lot of energy. If you put a lot >>>>>>>>> of current through the turns the mechanical forces eventually rip them >>>>>>>>> apart, but that's a very different regime. >>>>>>>>> >>>>>>>> >>>>>>>> Because an air-core 12.5 kH inductor is *big*. >>>>>>> >>>>>>> As I managed to work out, after an unfortunate slip of the mind. >>>>>>> >>>>>>> 12.5KH is much bigger inductance than you would want or need. 100sec to >>>>>>> discharge a capacitor is much too long. >>>>>>> >>>>>>> 5H and and 1sec makes much more sense but the air-cored inductor would >>>>>>> still be impractically large. >>>>>>> >>>>>>> A carbonyl iron core might work >>>>>>> >>>>>>> https://www.rf-microwave.com/resources/products_attachments/67aa26a4a6d8c.pdf >>>>>>> >>>>>>> would need 16000 turns of 0.5mm OD copper wire to get to 5H. That's >>>>>>> about 34 layers of wire about 2600 metres long, and the series >>>>>>> resistance would be 230R, which is too high. >>>>>>> >>>>>>> 2.5mm OD wire might work, but that's only 100 tuns per layer, and 160 >>>>>>> layers would over-fill the winding space. >>>>>>> >>>>>>> A bigger core could accommodate more turns of thicker wire, but that >>>>>>> supplier doesn't do one. >>>>>>> >>>>>>> An iron tape core would offer more nH per root turn. They are >>>>>>> commercially available and in larger sizes >>>>>>> >>>>>>> https://www.transmart.net/current-transformer-cores.html >>>>>>> >>>>>>> but the web-site isn't all that transparent, and clearly aimed at >>>>>>> sophisticated users. >>>>>> >>>>>> You ignore simple rule of thumb: energy is more efficiently stored >>>>>> in air. So to get energy storage needed for critical >>>>>> damping you need inductor as big or bigger than air cored >>>>>> inductor. You need core because otherwise winding resistance >>>>>> is likely be too big for critical damping. >>>>>> >>>>>> It seems that inductor with EI core with the following dimensions >>>>>> could satisfy the needs: >>>>>> >>>>>> Surface of the central column: 200 cm^2. >>>>>> Side of cental column: 14.14 cm. >>>>>> Height of cental column: 21.21 cm. >>>>>> Width of winding window: 7.07 cm. >>>>>> Total height of core: 35.35 cm >>>>>> Total width of core: 42.42 cm >>>>>> Total volume of core: 16962.87 cm^3 >>>>>> Weight of the core: 129426.74 g >>>>>> Air gap: 1cm >>>>>> >>>>>> To get L = 5H needs 1727 turns. I get 1.43 Ohm as winding resistance. >>>>>> >>>>>> So I guess that if one really needed such an inductor it would >>>>>> be practical. But it is bulky. I am not sure if it is bigger >>>>>> than the capacitor bank, but I expect it to be heavier. >>>>>> >>>>> Which one of these specs represents the radius of the inductor? That >>>>> would be a great help in visualizing it. >>>> >>>> Imagine rectangular box of dimensions 43x36x30 (all 3 in centimeters). >>> >>> Cool. I wouldn't need a resistor. 130 KG of iron and copper could >>> absorb a lot of joules. >>> >>> The inductor was a great idea, Bill. >> >> Waldeck Hebisch may have designed an inductor, though he hasn't bothered >> to post a link to the data sheet for the EI cores he has in mind, and >> his claim that it needs an airgap isn't justified by any kind of argument. >> >> Toriodal cores made by winding iron tape (or thin strips of other >> high-permeability ferromagnetic material) offer more microHenries per >> turn,and saturate at higher magnetic fields that the ferrites he appears >> to have in mind. >> >> At the moment using an inductor to speed up the discharge process is >> looking like a bulky solution, but the capacitors you need to discharge >> quickly aren't exactly surface mount parts either. > > 130 KG is a lot of stuff. > > Engineers benefit from quickly discounting designs that are orders of > magnitude away from being sensible. As I have pointed out in a new thread, you can allow the inductor to saturate at the start of the discharge process. That lets you get away with quite a bit less iron and copper. Rejecting the approach too rapidly has blinded you to that particular option. You've compalined about people poisoning brain-storming sessions by being too sceptical too early, though here you are just being intellectually lazy. -- Bill Sloman, Sydney
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| From | john larkin <jl@glen--canyon.com> |
|---|---|
| Date | 2026-09-14 08:22 -0700 |
| Message-ID | <b84gal1dj2bbe33d196ir9dffe4k0ns58t@4ax.com> |
| In reply to | #747707 |
On Mon, 14 Sep 2026 15:59:55 +1000, Bill Sloman <bill.sloman@ieee.org> wrote: >On 14/09/2026 5:03 am, john larkin wrote: >> On Mon, 14 Sep 2026 01:28:04 +1000, Bill Sloman <bill.sloman@ieee.org> >> wrote: >> >>> On 14/09/2026 12:50 am, john larkin wrote: >>>> On Sun, 13 Sep 2026 03:11:25 -0000 (UTC), antispam@fricas.org (Waldek >>>> Hebisch) wrote: >>>> >>>>> Lane W <cactus_DAC@yahoo.com> wrote: >>>>>> Waldek Hebisch wrote: >>>>>>> Bill Sloman <bill.sloman@ieee.org> wrote: >>>>>>>> >>>>>>>> >>>>>>>> On 10/09/2026 7:10 am, Jeroen Belleman wrote: >>>>>>>>> On 9/9/26 17:32, Bill Sloman wrote: >>>>>>>>>> On 9/09/2026 10:25 pm, Jeroen Belleman wrote: >>>>>>>>>>> On 9/9/26 12:44, john larkin wrote: >>>>>>>>>>>> On Wed, 9 Sep 2026 09:51:57 -0000 (UTC), piglet >>>>>>>>>>>> <erichpwagner@hotmail.com> wrote: >>>>>>>>>>>> >>>>>>>>>>>>> Bill Sloman <bill.sloman@ieee.org> wrote: >>>>>>>>>>>>>> On 9/09/2026 5:56 am, john larkin wrote: >>>>>>>>>>>>>>> On Wed, 9 Sep 2026 03:09:41 +1000, Bill Sloman >>>>>>>>>>>>>>> <bill.sloman@ieee.org> >>>>>>>>>>>>>>> wrote: >>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> On 9/09/2026 1:00 am, john larkin wrote: >>>>>>>>>>>>>>>>> On Tue, 8 Sep 2026 17:35:24 +1000, Bill Sloman >>>>>>>>>>>>>>>>> <bill.sloman@ieee.org> >>>>>>>>>>>>>>>>> wrote: >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> On 8/09/2026 4:52 am, john larkin wrote: >>>>>>>>>>>>>>>>>>> On Mon, 7 Sep 2026 19:33:35 +0100, chrisq >>>>>>>>>>>>>>>>>>> <syseng@gfsys.co.uk> wrote: >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>> On 9/7/26 16:18, john larkin wrote: >>>>>>>>>>>>>>>>>>>>> Suppose we have a box with some big caps inside, for >>>>>>>>>>>>>>>>>>>>> example 0.2 >>>>>>>>>>>>>>>>>>>>> farads that run at about 200 volts. When AC power is off, >>>>>>>>>>>>>>>>>>>>> we want to >>>>>>>>>>>>>>>>>>>>> discharge them for several reasons. >>>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>>> Putting, say, a 1K resistor across them dissipates 40 watts >>>>>>>>>>>>>>>>>>>>> and has a >>>>>>>>>>>>>>>>>>>>> 200 second time constant. It will take many tau before the >>>>>>>>>>>>>>>>>>>>> voltage >>>>>>>>>>>>>>>>>>>>> gets low enough for people to poke around inside. >>>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>>> The ideal discharger would be a constant-current or even >>>>>>>>>>>>>>>>>>>>> better a >>>>>>>>>>>>>>>>>>>>> constant-power load, all the way down to zero volts. It >>>>>>>>>>>>>>>>>>>>> would be dumb, >>>>>>>>>>>>>>>>>>>>> not switched by some decision circuit or anything fancy >>>>>>>>>>>>>>>>>>>>> like that. >>>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>>> And of course we need several LEDs as warnings that the >>>>>>>>>>>>>>>>>>>>> thing is hot. >>>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>> What sort of design needs 0.2 Farad cap, at 200 volts ?. If >>>>>>>>>>>>>>>>>>>> you are >>>>>>>>>>>>>>>>>>>> working at that level, put in a cheap relay and a rated >>>>>>>>>>>>>>>>>>>> heatsink >>>>>>>>>>>>>>>>>>>> wirewound resistor to dump the energy, when the power goes off. >>>>>>>>>>>>>>>>>>>> Cheap, and lossless as well. Motor drive inverters often have >>>>>>>>>>>>>>>>>>>> big resistors to brake the motor. >>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>>> John Larkin >>>>>>>>>>>>>>>>>>>>> Highland Tech Glen Canyon Design Center >>>>>>>>>>>>>>>>>>>>> Lunatic Fringe Electronics >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> It's a 1500 amp laser driver. >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> The input to our box is DC, from an external power supply. >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> I do want a circuit that's foolproof, that always discharges >>>>>>>>>>>>>>>>>>> the caps >>>>>>>>>>>>>>>>>>> but doen't often go up in flames. >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> A resistor makes an exponential decay which could be a very >>>>>>>>>>>>>>>>>>> long time >>>>>>>>>>>>>>>>>>> to get down to safe levels. >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> But a resistor plus an inductor could give a critically damped >>>>>>>>>>>>>>>>>> decay, >>>>>>>>>>>>>>>>>> which would be quite a bit faster. I don't know enough about >>>>>>>>>>>>>>>>>> the circuit >>>>>>>>>>>>>>>>>> to be prepared to try to work out how much inductance you'd >>>>>>>>>>>>>>>>>> need, and >>>>>>>>>>>>>>>>>> you clearly can't be bothered. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> Won't be bothered. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> I thought the group might like a circuit design problem once >>>>>>>>>>>>>>>>>>> in a >>>>>>>>>>>>>>>>>>> while, a break from politics. >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> But you don't do circuit design, and this sort of question >>>>>>>>>>>>>>>>>> makes it >>>>>>>>>>>>>>>>>> obvious why you don't. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> The inductor suggestion is hilarious. Thanks. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> It's elementary circuit theory, which you should have been >>>>>>>>>>>>>>>> taught and I >>>>>>>>>>>>>>>> had to read about. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> If you discharge a capacitor through a resistor, the voltage decays >>>>>>>>>>>>>>>> exponentially. If you put an inductor in series with the >>>>>>>>>>>>>>>> resistor the >>>>>>>>>>>>>>>> voltage decay is a more complicated function of time. If you >>>>>>>>>>>>>>>> chose the >>>>>>>>>>>>>>>> resistance and the inductance to create a critically damped >>>>>>>>>>>>>>>> circuit, the >>>>>>>>>>>>>>>> voltage across the capacitor will eventually decay more rapidly >>>>>>>>>>>>>>>> than >>>>>>>>>>>>>>>> you'd see with just the resistor. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> Try reading about Laplace transforms. That's a pretty hilarious >>>>>>>>>>>>>>>> suggestion to direct at you, but you are the butt of the joke. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Oh, RLC circuits are no mystery. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> What's funny about the suggestion is the size of the inductor it >>>>>>>>>>>>>>> would >>>>>>>>>>>>>>> need. >>>>>>>>>>>>>> >>>>>>>>>>>>>> Which you haven't worked out. I spent a few minutes last night >>>>>>>>>>>>>> trying to >>>>>>>>>>>>>> work out what I could buy off the shelf from element-14 (the >>>>>>>>>>>>>> Australian >>>>>>>>>>>>>> branch of Newark) but their web-site has turned cranky in recent >>>>>>>>>>>>>> months. >>>>>>>>>>>>>> >>>>>>>>>>>>>> The value of the inductance isn't fixed - that and the resistor >>>>>>>>>>>>>> can be >>>>>>>>>>>>>> be chosen to get a critically damped LCR, and I figured that I'd >>>>>>>>>>>>>> start >>>>>>>>>>>>>> playing with an inductor I could buy. >>>>>>>>>>>>>> >>>>>>>>>>>>>> You might end up with a non-progressively wound air-cored toroid. >>>>>>>>>>>>>> With a >>>>>>>>>>>>>> 0.2F capacitor the parallel capacitance of the inductor isn't >>>>>>>>>>>>>> going to >>>>>>>>>>>>>> be an issue, and the winding resistance could be your damping >>>>>>>>>>>>>> resistor. >>>>>>>>>>>>>> >>>>>>>>>>>>>> 4kJ is a fair bit of energy, but you can get copper quite hot >>>>>>>>>>>>>> before it >>>>>>>>>>>>>> explodes. It wouldn't stay hot for long. >>>>>>>>>>>>>> >>>>>>>>>>>>> >>>>>>>>>>>>> I haven’t calculated what ballpark inductance might be required but >>>>>>>>>>>>> is air >>>>>>>>>>>>> core even feasible for that? >>>>>>>>>>>> >>>>>>>>>>>> If it were about the size of a truck maybe. >>>>>>>>>>>> >>>>>>>>>>>> You can estimate the inductance in your head. To discharge 0.2F in, >>>>>>>>>>>> say 100 seconds, you need 500 ohms. That would of course be the tau of >>>>>>>>>>>> an exponential decay. Adding an inductor would crisp that up. >>>>>>>>>>>> >>>>>>>>>>>> R*C = 100 seconds so we want L/R to be in that ballpark. >>>>>>>>>> >>>>>>>>>> 100 seconds is a lot too long from a safety point of view >>>>>>>>>> >>>>>>>>>>>> So L is around 50,000 H. >>>>>>>>>> >>>>>>>>>> If you start at the wrong end. >>>>>>>>>> >>>>>>>>>>>> Check Digikey for that. >>>>>>>>>>> >>>>>>>>>>> Critical damping happens when the expression for the impedance of >>>>>>>>>>> the series RLC has two identical roots. This happens when L = R^2C/4, >>>>>>>>>>> near enough, so L should be 12.5 kH. >>>>>>>>>> >>>>>>>>>> You can vary both L and R. A much shorter time constant means a much >>>>>>>>>> smaller inductor >>>>>>>>>> >>>>>>>>>> I dug out my copy of Grover and thought about a 5H air-cored inductor. >>>>>>>>>> >>>>>>>>>> 5H - a 1 sec time constant - would be practicable - but big. You'd >>>>>>>>>> need a great deal of copper wire to make it work. >>>>>>>>>> >>>>>>>>>> It might be worth thinking about an iron-cored inductor. We are >>>>>>>>>> looking at a fairly slow event so the current induced in the iron >>>>>>>>>> would be just one more dissipation mode. >>>>>>>>>> >>>>>>>>>> 0.5H might work. The time constant of 0.32 sec means that your 4kJ >>>>>>>>>> looks like 13kW while it is dissipating, but it would be being >>>>>>>>>> dissipated in what could be a fairly substantial resistor which >>>>>>>>>> wouldn't warm up much and would have time to cool off. >>>>>>>>>> >>>>>>>>>>> With the initial voltage 200V, it will need to briefly store just >>>>>>>>>>> short of 600 J. That doesn't look like a practical solution. >>>>>>>>>> >>>>>>>>>> Why not? Air-cored coils can store a lot of energy. If you put a lot >>>>>>>>>> of current through the turns the mechanical forces eventually rip them >>>>>>>>>> apart, but that's a very different regime. >>>>>>>>>> >>>>>>>>> >>>>>>>>> Because an air-core 12.5 kH inductor is *big*. >>>>>>>> >>>>>>>> As I managed to work out, after an unfortunate slip of the mind. >>>>>>>> >>>>>>>> 12.5KH is much bigger inductance than you would want or need. 100sec to >>>>>>>> discharge a capacitor is much too long. >>>>>>>> >>>>>>>> 5H and and 1sec makes much more sense but the air-cored inductor would >>>>>>>> still be impractically large. >>>>>>>> >>>>>>>> A carbonyl iron core might work >>>>>>>> >>>>>>>> https://www.rf-microwave.com/resources/products_attachments/67aa26a4a6d8c.pdf >>>>>>>> >>>>>>>> would need 16000 turns of 0.5mm OD copper wire to get to 5H. That's >>>>>>>> about 34 layers of wire about 2600 metres long, and the series >>>>>>>> resistance would be 230R, which is too high. >>>>>>>> >>>>>>>> 2.5mm OD wire might work, but that's only 100 tuns per layer, and 160 >>>>>>>> layers would over-fill the winding space. >>>>>>>> >>>>>>>> A bigger core could accommodate more turns of thicker wire, but that >>>>>>>> supplier doesn't do one. >>>>>>>> >>>>>>>> An iron tape core would offer more nH per root turn. They are >>>>>>>> commercially available and in larger sizes >>>>>>>> >>>>>>>> https://www.transmart.net/current-transformer-cores.html >>>>>>>> >>>>>>>> but the web-site isn't all that transparent, and clearly aimed at >>>>>>>> sophisticated users. >>>>>>> >>>>>>> You ignore simple rule of thumb: energy is more efficiently stored >>>>>>> in air. So to get energy storage needed for critical >>>>>>> damping you need inductor as big or bigger than air cored >>>>>>> inductor. You need core because otherwise winding resistance >>>>>>> is likely be too big for critical damping. >>>>>>> >>>>>>> It seems that inductor with EI core with the following dimensions >>>>>>> could satisfy the needs: >>>>>>> >>>>>>> Surface of the central column: 200 cm^2. >>>>>>> Side of cental column: 14.14 cm. >>>>>>> Height of cental column: 21.21 cm. >>>>>>> Width of winding window: 7.07 cm. >>>>>>> Total height of core: 35.35 cm >>>>>>> Total width of core: 42.42 cm >>>>>>> Total volume of core: 16962.87 cm^3 >>>>>>> Weight of the core: 129426.74 g >>>>>>> Air gap: 1cm >>>>>>> >>>>>>> To get L = 5H needs 1727 turns. I get 1.43 Ohm as winding resistance. >>>>>>> >>>>>>> So I guess that if one really needed such an inductor it would >>>>>>> be practical. But it is bulky. I am not sure if it is bigger >>>>>>> than the capacitor bank, but I expect it to be heavier. >>>>>>> >>>>>> Which one of these specs represents the radius of the inductor? That >>>>>> would be a great help in visualizing it. >>>>> >>>>> Imagine rectangular box of dimensions 43x36x30 (all 3 in centimeters). >>>> >>>> Cool. I wouldn't need a resistor. 130 KG of iron and copper could >>>> absorb a lot of joules. >>>> >>>> The inductor was a great idea, Bill. >>> >>> Waldeck Hebisch may have designed an inductor, though he hasn't bothered >>> to post a link to the data sheet for the EI cores he has in mind, and >>> his claim that it needs an airgap isn't justified by any kind of argument. >>> >>> Toriodal cores made by winding iron tape (or thin strips of other >>> high-permeability ferromagnetic material) offer more microHenries per >>> turn,and saturate at higher magnetic fields that the ferrites he appears >>> to have in mind. >>> >>> At the moment using an inductor to speed up the discharge process is >>> looking like a bulky solution, but the capacitors you need to discharge >>> quickly aren't exactly surface mount parts either. >> >> 130 KG is a lot of stuff. >> >> Engineers benefit from quickly discounting designs that are orders of >> magnitude away from being sensible. > >As I have pointed out in a new thread, you can allow the inductor to >saturate at the start of the discharge process. That lets you get away >with quite a bit less iron and copper. > >Rejecting the approach too rapidly has blinded you to that particular >option. You've compalined about people poisoning brain-storming sessions >by being too sceptical too early, though here you are just being >intellectually lazy. If you have so much energy, design it. John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
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| From | Bill Sloman <bill.sloman@ieee.org> |
|---|---|
| Date | 2026-09-15 18:31 +1000 |
| Message-ID | <118avoq$281am$5@dont-email.me> |
| In reply to | #747730 |
On 15/09/2026 1:22 am, john larkin wrote: > On Mon, 14 Sep 2026 15:59:55 +1000, Bill Sloman <bill.sloman@ieee.org> > wrote: > >> On 14/09/2026 5:03 am, john larkin wrote: >>> On Mon, 14 Sep 2026 01:28:04 +1000, Bill Sloman <bill.sloman@ieee.org> >>> wrote: >>> >>>> On 14/09/2026 12:50 am, john larkin wrote: >>>>> On Sun, 13 Sep 2026 03:11:25 -0000 (UTC), antispam@fricas.org (Waldek >>>>> Hebisch) wrote: >>>>> >>>>>> Lane W <cactus_DAC@yahoo.com> wrote: >>>>>>> Waldek Hebisch wrote: >>>>>>>> Bill Sloman <bill.sloman@ieee.org> wrote: >>>>>>>>> >>>>>>>>> >>>>>>>>> On 10/09/2026 7:10 am, Jeroen Belleman wrote: >>>>>>>>>> On 9/9/26 17:32, Bill Sloman wrote: >>>>>>>>>>> On 9/09/2026 10:25 pm, Jeroen Belleman wrote: >>>>>>>>>>>> On 9/9/26 12:44, john larkin wrote: >>>>>>>>>>>>> On Wed, 9 Sep 2026 09:51:57 -0000 (UTC), piglet >>>>>>>>>>>>> <erichpwagner@hotmail.com> wrote: >>>>>>>>>>>>> >>>>>>>>>>>>>> Bill Sloman <bill.sloman@ieee.org> wrote: >>>>>>>>>>>>>>> On 9/09/2026 5:56 am, john larkin wrote: >>>>>>>>>>>>>>>> On Wed, 9 Sep 2026 03:09:41 +1000, Bill Sloman >>>>>>>>>>>>>>>> <bill.sloman@ieee.org> >>>>>>>>>>>>>>>> wrote: >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> On 9/09/2026 1:00 am, john larkin wrote: >>>>>>>>>>>>>>>>>> On Tue, 8 Sep 2026 17:35:24 +1000, Bill Sloman >>>>>>>>>>>>>>>>>> <bill.sloman@ieee.org> >>>>>>>>>>>>>>>>>> wrote: >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> On 8/09/2026 4:52 am, john larkin wrote: >>>>>>>>>>>>>>>>>>>> On Mon, 7 Sep 2026 19:33:35 +0100, chrisq >>>>>>>>>>>>>>>>>>>> <syseng@gfsys.co.uk> wrote: >>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>>> On 9/7/26 16:18, john larkin wrote: >>>>>>>>>>>>>>>>>>>>>> Suppose we have a box with some big caps inside, for >>>>>>>>>>>>>>>>>>>>>> example 0.2 >>>>>>>>>>>>>>>>>>>>>> farads that run at about 200 volts. When AC power is off, >>>>>>>>>>>>>>>>>>>>>> we want to >>>>>>>>>>>>>>>>>>>>>> discharge them for several reasons. >>>>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>>>> Putting, say, a 1K resistor across them dissipates 40 watts >>>>>>>>>>>>>>>>>>>>>> and has a >>>>>>>>>>>>>>>>>>>>>> 200 second time constant. It will take many tau before the >>>>>>>>>>>>>>>>>>>>>> voltage >>>>>>>>>>>>>>>>>>>>>> gets low enough for people to poke around inside. >>>>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>>>> The ideal discharger would be a constant-current or even >>>>>>>>>>>>>>>>>>>>>> better a >>>>>>>>>>>>>>>>>>>>>> constant-power load, all the way down to zero volts. It >>>>>>>>>>>>>>>>>>>>>> would be dumb, >>>>>>>>>>>>>>>>>>>>>> not switched by some decision circuit or anything fancy >>>>>>>>>>>>>>>>>>>>>> like that. >>>>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>>>> And of course we need several LEDs as warnings that the >>>>>>>>>>>>>>>>>>>>>> thing is hot. >>>>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>>> What sort of design needs 0.2 Farad cap, at 200 volts ?. If >>>>>>>>>>>>>>>>>>>>> you are >>>>>>>>>>>>>>>>>>>>> working at that level, put in a cheap relay and a rated >>>>>>>>>>>>>>>>>>>>> heatsink >>>>>>>>>>>>>>>>>>>>> wirewound resistor to dump the energy, when the power goes off. >>>>>>>>>>>>>>>>>>>>> Cheap, and lossless as well. Motor drive inverters often have >>>>>>>>>>>>>>>>>>>>> big resistors to brake the motor. >>>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>>>> John Larkin >>>>>>>>>>>>>>>>>>>>>> Highland Tech Glen Canyon Design Center >>>>>>>>>>>>>>>>>>>>>> Lunatic Fringe Electronics >>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>> It's a 1500 amp laser driver. >>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>> The input to our box is DC, from an external power supply. >>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>> I do want a circuit that's foolproof, that always discharges >>>>>>>>>>>>>>>>>>>> the caps >>>>>>>>>>>>>>>>>>>> but doen't often go up in flames. >>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>> A resistor makes an exponential decay which could be a very >>>>>>>>>>>>>>>>>>>> long time >>>>>>>>>>>>>>>>>>>> to get down to safe levels. >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> But a resistor plus an inductor could give a critically damped >>>>>>>>>>>>>>>>>>> decay, >>>>>>>>>>>>>>>>>>> which would be quite a bit faster. I don't know enough about >>>>>>>>>>>>>>>>>>> the circuit >>>>>>>>>>>>>>>>>>> to be prepared to try to work out how much inductance you'd >>>>>>>>>>>>>>>>>>> need, and >>>>>>>>>>>>>>>>>>> you clearly can't be bothered. >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> Won't be bothered. >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>> I thought the group might like a circuit design problem once >>>>>>>>>>>>>>>>>>>> in a >>>>>>>>>>>>>>>>>>>> while, a break from politics. >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> But you don't do circuit design, and this sort of question >>>>>>>>>>>>>>>>>>> makes it >>>>>>>>>>>>>>>>>>> obvious why you don't. >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> The inductor suggestion is hilarious. Thanks. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> It's elementary circuit theory, which you should have been >>>>>>>>>>>>>>>>> taught and I >>>>>>>>>>>>>>>>> had to read about. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> If you discharge a capacitor through a resistor, the voltage decays >>>>>>>>>>>>>>>>> exponentially. If you put an inductor in series with the >>>>>>>>>>>>>>>>> resistor the >>>>>>>>>>>>>>>>> voltage decay is a more complicated function of time. If you >>>>>>>>>>>>>>>>> chose the >>>>>>>>>>>>>>>>> resistance and the inductance to create a critically damped >>>>>>>>>>>>>>>>> circuit, the >>>>>>>>>>>>>>>>> voltage across the capacitor will eventually decay more rapidly >>>>>>>>>>>>>>>>> than >>>>>>>>>>>>>>>>> you'd see with just the resistor. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> Try reading about Laplace transforms. That's a pretty hilarious >>>>>>>>>>>>>>>>> suggestion to direct at you, but you are the butt of the joke. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> Oh, RLC circuits are no mystery. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> What's funny about the suggestion is the size of the inductor it >>>>>>>>>>>>>>>> would >>>>>>>>>>>>>>>> need. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Which you haven't worked out. I spent a few minutes last night >>>>>>>>>>>>>>> trying to >>>>>>>>>>>>>>> work out what I could buy off the shelf from element-14 (the >>>>>>>>>>>>>>> Australian >>>>>>>>>>>>>>> branch of Newark) but their web-site has turned cranky in recent >>>>>>>>>>>>>>> months. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> The value of the inductance isn't fixed - that and the resistor >>>>>>>>>>>>>>> can be >>>>>>>>>>>>>>> be chosen to get a critically damped LCR, and I figured that I'd >>>>>>>>>>>>>>> start >>>>>>>>>>>>>>> playing with an inductor I could buy. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> You might end up with a non-progressively wound air-cored toroid. >>>>>>>>>>>>>>> With a >>>>>>>>>>>>>>> 0.2F capacitor the parallel capacitance of the inductor isn't >>>>>>>>>>>>>>> going to >>>>>>>>>>>>>>> be an issue, and the winding resistance could be your damping >>>>>>>>>>>>>>> resistor. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> 4kJ is a fair bit of energy, but you can get copper quite hot >>>>>>>>>>>>>>> before it >>>>>>>>>>>>>>> explodes. It wouldn't stay hot for long. >>>>>>>>>>>>>>> >>>>>>>>>>>>>> >>>>>>>>>>>>>> I haven’t calculated what ballpark inductance might be required but >>>>>>>>>>>>>> is air >>>>>>>>>>>>>> core even feasible for that? >>>>>>>>>>>>> >>>>>>>>>>>>> If it were about the size of a truck maybe. >>>>>>>>>>>>> >>>>>>>>>>>>> You can estimate the inductance in your head. To discharge 0.2F in, >>>>>>>>>>>>> say 100 seconds, you need 500 ohms. That would of course be the tau of >>>>>>>>>>>>> an exponential decay. Adding an inductor would crisp that up. >>>>>>>>>>>>> >>>>>>>>>>>>> R*C = 100 seconds so we want L/R to be in that ballpark. >>>>>>>>>>> >>>>>>>>>>> 100 seconds is a lot too long from a safety point of view >>>>>>>>>>> >>>>>>>>>>>>> So L is around 50,000 H. >>>>>>>>>>> >>>>>>>>>>> If you start at the wrong end. >>>>>>>>>>> >>>>>>>>>>>>> Check Digikey for that. >>>>>>>>>>>> >>>>>>>>>>>> Critical damping happens when the expression for the impedance of >>>>>>>>>>>> the series RLC has two identical roots. This happens when L = R^2C/4, >>>>>>>>>>>> near enough, so L should be 12.5 kH. >>>>>>>>>>> >>>>>>>>>>> You can vary both L and R. A much shorter time constant means a much >>>>>>>>>>> smaller inductor >>>>>>>>>>> >>>>>>>>>>> I dug out my copy of Grover and thought about a 5H air-cored inductor. >>>>>>>>>>> >>>>>>>>>>> 5H - a 1 sec time constant - would be practicable - but big. You'd >>>>>>>>>>> need a great deal of copper wire to make it work. >>>>>>>>>>> >>>>>>>>>>> It might be worth thinking about an iron-cored inductor. We are >>>>>>>>>>> looking at a fairly slow event so the current induced in the iron >>>>>>>>>>> would be just one more dissipation mode. >>>>>>>>>>> >>>>>>>>>>> 0.5H might work. The time constant of 0.32 sec means that your 4kJ >>>>>>>>>>> looks like 13kW while it is dissipating, but it would be being >>>>>>>>>>> dissipated in what could be a fairly substantial resistor which >>>>>>>>>>> wouldn't warm up much and would have time to cool off. >>>>>>>>>>> >>>>>>>>>>>> With the initial voltage 200V, it will need to briefly store just >>>>>>>>>>>> short of 600 J. That doesn't look like a practical solution. >>>>>>>>>>> >>>>>>>>>>> Why not? Air-cored coils can store a lot of energy. If you put a lot >>>>>>>>>>> of current through the turns the mechanical forces eventually rip them >>>>>>>>>>> apart, but that's a very different regime. >>>>>>>>>>> >>>>>>>>>> >>>>>>>>>> Because an air-core 12.5 kH inductor is *big*. >>>>>>>>> >>>>>>>>> As I managed to work out, after an unfortunate slip of the mind. >>>>>>>>> >>>>>>>>> 12.5KH is much bigger inductance than you would want or need. 100sec to >>>>>>>>> discharge a capacitor is much too long. >>>>>>>>> >>>>>>>>> 5H and and 1sec makes much more sense but the air-cored inductor would >>>>>>>>> still be impractically large. >>>>>>>>> >>>>>>>>> A carbonyl iron core might work >>>>>>>>> >>>>>>>>> https://www.rf-microwave.com/resources/products_attachments/67aa26a4a6d8c.pdf >>>>>>>>> >>>>>>>>> would need 16000 turns of 0.5mm OD copper wire to get to 5H. That's >>>>>>>>> about 34 layers of wire about 2600 metres long, and the series >>>>>>>>> resistance would be 230R, which is too high. >>>>>>>>> >>>>>>>>> 2.5mm OD wire might work, but that's only 100 tuns per layer, and 160 >>>>>>>>> layers would over-fill the winding space. >>>>>>>>> >>>>>>>>> A bigger core could accommodate more turns of thicker wire, but that >>>>>>>>> supplier doesn't do one. >>>>>>>>> >>>>>>>>> An iron tape core would offer more nH per root turn. They are >>>>>>>>> commercially available and in larger sizes >>>>>>>>> >>>>>>>>> https://www.transmart.net/current-transformer-cores.html >>>>>>>>> >>>>>>>>> but the web-site isn't all that transparent, and clearly aimed at >>>>>>>>> sophisticated users. >>>>>>>> >>>>>>>> You ignore simple rule of thumb: energy is more efficiently stored >>>>>>>> in air. So to get energy storage needed for critical >>>>>>>> damping you need inductor as big or bigger than air cored >>>>>>>> inductor. You need core because otherwise winding resistance >>>>>>>> is likely be too big for critical damping. >>>>>>>> >>>>>>>> It seems that inductor with EI core with the following dimensions >>>>>>>> could satisfy the needs: >>>>>>>> >>>>>>>> Surface of the central column: 200 cm^2. >>>>>>>> Side of cental column: 14.14 cm. >>>>>>>> Height of cental column: 21.21 cm. >>>>>>>> Width of winding window: 7.07 cm. >>>>>>>> Total height of core: 35.35 cm >>>>>>>> Total width of core: 42.42 cm >>>>>>>> Total volume of core: 16962.87 cm^3 >>>>>>>> Weight of the core: 129426.74 g >>>>>>>> Air gap: 1cm >>>>>>>> >>>>>>>> To get L = 5H needs 1727 turns. I get 1.43 Ohm as winding resistance. >>>>>>>> >>>>>>>> So I guess that if one really needed such an inductor it would >>>>>>>> be practical. But it is bulky. I am not sure if it is bigger >>>>>>>> than the capacitor bank, but I expect it to be heavier. >>>>>>>> >>>>>>> Which one of these specs represents the radius of the inductor? That >>>>>>> would be a great help in visualizing it. >>>>>> >>>>>> Imagine rectangular box of dimensions 43x36x30 (all 3 in centimeters). >>>>> >>>>> Cool. I wouldn't need a resistor. 130 KG of iron and copper could >>>>> absorb a lot of joules. >>>>> >>>>> The inductor was a great idea, Bill. >>>> >>>> Waldeck Hebisch may have designed an inductor, though he hasn't bothered >>>> to post a link to the data sheet for the EI cores he has in mind, and >>>> his claim that it needs an airgap isn't justified by any kind of argument. >>>> >>>> Toriodal cores made by winding iron tape (or thin strips of other >>>> high-permeability ferromagnetic material) offer more microHenries per >>>> turn,and saturate at higher magnetic fields that the ferrites he appears >>>> to have in mind. >>>> >>>> At the moment using an inductor to speed up the discharge process is >>>> looking like a bulky solution, but the capacitors you need to discharge >>>> quickly aren't exactly surface mount parts either. >>> >>> 130 KG is a lot of stuff. >>> >>> Engineers benefit from quickly discounting designs that are orders of >>> magnitude away from being sensible. >> >> As I have pointed out in a new thread, you can allow the inductor to >> saturate at the start of the discharge process. That lets you get away >> with quite a bit less iron and copper. >> >> Rejecting the approach too rapidly has blinded you to that particular >> option. You've complained about people poisoning brain-storming sessions >> by being too sceptical too early, though here you are just being >> intellectually lazy. > > If you have so much energy, design it. Only for money. I'm perfectly happy with the very limited glory I've already got. -- Bill Sloman, Sydney
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| From | john larkin <jl@glen--canyon.com> |
|---|---|
| Date | 2026-09-12 17:59 -0700 |
| Message-ID | <p9tbalhhevknva0ct7bnd5sp19gdq0o2pd@4ax.com> |
| In reply to | #747637 |
On Sun, 13 Sep 2026 00:27:24 -0000 (UTC), antispam@fricas.org (Waldek Hebisch) wrote: >Bill Sloman <bill.sloman@ieee.org> wrote: >> >> >> On 10/09/2026 7:10 am, Jeroen Belleman wrote: >>> On 9/9/26 17:32, Bill Sloman wrote: >>>> On 9/09/2026 10:25 pm, Jeroen Belleman wrote: >>>>> On 9/9/26 12:44, john larkin wrote: >>>>>> On Wed, 9 Sep 2026 09:51:57 -0000 (UTC), piglet >>>>>> <erichpwagner@hotmail.com> wrote: >>>>>> >>>>>>> Bill Sloman <bill.sloman@ieee.org> wrote: >>>>>>>> On 9/09/2026 5:56 am, john larkin wrote: >>>>>>>>> On Wed, 9 Sep 2026 03:09:41 +1000, Bill Sloman >>>>>>>>> <bill.sloman@ieee.org> >>>>>>>>> wrote: >>>>>>>>> >>>>>>>>>> On 9/09/2026 1:00 am, john larkin wrote: >>>>>>>>>>> On Tue, 8 Sep 2026 17:35:24 +1000, Bill Sloman >>>>>>>>>>> <bill.sloman@ieee.org> >>>>>>>>>>> wrote: >>>>>>>>>>> >>>>>>>>>>>> On 8/09/2026 4:52 am, john larkin wrote: >>>>>>>>>>>>> On Mon, 7 Sep 2026 19:33:35 +0100, chrisq >>>>>>>>>>>>> <syseng@gfsys.co.uk> wrote: >>>>>>>>>>>>> >>>>>>>>>>>>>> On 9/7/26 16:18, john larkin wrote: >>>>>>>>>>>>>>> Suppose we have a box with some big caps inside, for >>>>>>>>>>>>>>> example 0.2 >>>>>>>>>>>>>>> farads that run at about 200 volts. When AC power is off, >>>>>>>>>>>>>>> we want to >>>>>>>>>>>>>>> discharge them for several reasons. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Putting, say, a 1K resistor across them dissipates 40 watts >>>>>>>>>>>>>>> and has a >>>>>>>>>>>>>>> 200 second time constant. It will take many tau before the >>>>>>>>>>>>>>> voltage >>>>>>>>>>>>>>> gets low enough for people to poke around inside. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> The ideal discharger would be a constant-current or even >>>>>>>>>>>>>>> better a >>>>>>>>>>>>>>> constant-power load, all the way down to zero volts. It >>>>>>>>>>>>>>> would be dumb, >>>>>>>>>>>>>>> not switched by some decision circuit or anything fancy >>>>>>>>>>>>>>> like that. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> And of course we need several LEDs as warnings that the >>>>>>>>>>>>>>> thing is hot. >>>>>>>>>>>>>>> >>>>>>>>>>>>>> >>>>>>>>>>>>>> What sort of design needs 0.2 Farad cap, at 200 volts ?. If >>>>>>>>>>>>>> you are >>>>>>>>>>>>>> working at that level, put in a cheap relay and a rated >>>>>>>>>>>>>> heatsink >>>>>>>>>>>>>> wirewound resistor to dump the energy, when the power goes off. >>>>>>>>>>>>>> Cheap, and lossless as well. Motor drive inverters often have >>>>>>>>>>>>>> big resistors to brake the motor. >>>>>>>>>>>>>> >>>>>>>>>>>>>> >>>>>>>>>>>>>>> John Larkin >>>>>>>>>>>>>>> Highland Tech Glen Canyon Design Center >>>>>>>>>>>>>>> Lunatic Fringe Electronics >>>>>>>>>>>>> >>>>>>>>>>>>> It's a 1500 amp laser driver. >>>>>>>>>>>>> >>>>>>>>>>>>> The input to our box is DC, from an external power supply. >>>>>>>>>>>>> >>>>>>>>>>>>> I do want a circuit that's foolproof, that always discharges >>>>>>>>>>>>> the caps >>>>>>>>>>>>> but doen't often go up in flames. >>>>>>>>>>>>> >>>>>>>>>>>>> A resistor makes an exponential decay which could be a very >>>>>>>>>>>>> long time >>>>>>>>>>>>> to get down to safe levels. >>>>>>>>>>>> >>>>>>>>>>>> But a resistor plus an inductor could give a critically damped >>>>>>>>>>>> decay, >>>>>>>>>>>> which would be quite a bit faster. I don't know enough about >>>>>>>>>>>> the circuit >>>>>>>>>>>> to be prepared to try to work out how much inductance you'd >>>>>>>>>>>> need, and >>>>>>>>>>>> you clearly can't be bothered. >>>>>>>>>>> >>>>>>>>>>> Won't be bothered. >>>>>>>>>>> >>>>>>>>>>>> >>>>>>>>>>>>> I thought the group might like a circuit design problem once >>>>>>>>>>>>> in a >>>>>>>>>>>>> while, a break from politics. >>>>>>>>>>>> >>>>>>>>>>>> But you don't do circuit design, and this sort of question >>>>>>>>>>>> makes it >>>>>>>>>>>> obvious why you don't. >>>>>>>>>>> >>>>>>>>>>> The inductor suggestion is hilarious. Thanks. >>>>>>>>>> >>>>>>>>>> It's elementary circuit theory, which you should have been >>>>>>>>>> taught and I >>>>>>>>>> had to read about. >>>>>>>>>> >>>>>>>>>> If you discharge a capacitor through a resistor, the voltage decays >>>>>>>>>> exponentially. If you put an inductor in series with the >>>>>>>>>> resistor the >>>>>>>>>> voltage decay is a more complicated function of time. If you >>>>>>>>>> chose the >>>>>>>>>> resistance and the inductance to create a critically damped >>>>>>>>>> circuit, the >>>>>>>>>> voltage across the capacitor will eventually decay more rapidly >>>>>>>>>> than >>>>>>>>>> you'd see with just the resistor. >>>>>>>>>> >>>>>>>>>> Try reading about Laplace transforms. That's a pretty hilarious >>>>>>>>>> suggestion to direct at you, but you are the butt of the joke. >>>>>>>>> >>>>>>>>> Oh, RLC circuits are no mystery. >>>>>>>>> >>>>>>>>> What's funny about the suggestion is the size of the inductor it >>>>>>>>> would >>>>>>>>> need. >>>>>>>> >>>>>>>> Which you haven't worked out. I spent a few minutes last night >>>>>>>> trying to >>>>>>>> work out what I could buy off the shelf from element-14 (the >>>>>>>> Australian >>>>>>>> branch of Newark) but their web-site has turned cranky in recent >>>>>>>> months. >>>>>>>> >>>>>>>> The value of the inductance isn't fixed - that and the resistor >>>>>>>> can be >>>>>>>> be chosen to get a critically damped LCR, and I figured that I'd >>>>>>>> start >>>>>>>> playing with an inductor I could buy. >>>>>>>> >>>>>>>> You might end up with a non-progressively wound air-cored toroid. >>>>>>>> With a >>>>>>>> 0.2F capacitor the parallel capacitance of the inductor isn't >>>>>>>> going to >>>>>>>> be an issue, and the winding resistance could be your damping >>>>>>>> resistor. >>>>>>>> >>>>>>>> 4kJ is a fair bit of energy, but you can get copper quite hot >>>>>>>> before it >>>>>>>> explodes. It wouldn't stay hot for long. >>>>>>>> >>>>>>> >>>>>>> I haven’t calculated what ballpark inductance might be required but >>>>>>> is air >>>>>>> core even feasible for that? >>>>>> >>>>>> If it were about the size of a truck maybe. >>>>>> >>>>>> You can estimate the inductance in your head. To discharge 0.2F in, >>>>>> say 100 seconds, you need 500 ohms. That would of course be the tau of >>>>>> an exponential decay. Adding an inductor would crisp that up. >>>>>> >>>>>> R*C = 100 seconds so we want L/R to be in that ballpark. >>>> >>>> 100 seconds is a lot too long from a safety point of view >>>> >>>>>> So L is around 50,000 H. >>>> >>>> If you start at the wrong end. >>>> >>>>>> Check Digikey for that. >>>>> >>>>> Critical damping happens when the expression for the impedance of >>>>> the series RLC has two identical roots. This happens when L = R^2C/4, >>>>> near enough, so L should be 12.5 kH. >>>> >>>> You can vary both L and R. A much shorter time constant means a much >>>> smaller inductor >>>> >>>> I dug out my copy of Grover and thought about a 5H air-cored inductor. >>>> >>>> 5H - a 1 sec time constant - would be practicable - but big. You'd >>>> need a great deal of copper wire to make it work. >>>> >>>> It might be worth thinking about an iron-cored inductor. We are >>>> looking at a fairly slow event so the current induced in the iron >>>> would be just one more dissipation mode. >>>> >>>> 0.5H might work. The time constant of 0.32 sec means that your 4kJ >>>> looks like 13kW while it is dissipating, but it would be being >>>> dissipated in what could be a fairly substantial resistor which >>>> wouldn't warm up much and would have time to cool off. >>>> >>>>> With the initial voltage 200V, it will need to briefly store just >>>>> short of 600 J. That doesn't look like a practical solution. >>>> >>>> Why not? Air-cored coils can store a lot of energy. If you put a lot >>>> of current through the turns the mechanical forces eventually rip them >>>> apart, but that's a very different regime. >>>> >>> >>> Because an air-core 12.5 kH inductor is *big*. >> >> As I managed to work out, after an unfortunate slip of the mind. >> >> 12.5KH is much bigger inductance than you would want or need. 100sec to >> discharge a capacitor is much too long. >> >> 5H and and 1sec makes much more sense but the air-cored inductor would >> still be impractically large. >> >> A carbonyl iron core might work >> >> https://www.rf-microwave.com/resources/products_attachments/67aa26a4a6d8c.pdf >> >> would need 16000 turns of 0.5mm OD copper wire to get to 5H. That's >> about 34 layers of wire about 2600 metres long, and the series >> resistance would be 230R, which is too high. >> >> 2.5mm OD wire might work, but that's only 100 tuns per layer, and 160 >> layers would over-fill the winding space. >> >> A bigger core could accommodate more turns of thicker wire, but that >> supplier doesn't do one. >> >> An iron tape core would offer more nH per root turn. They are >> commercially available and in larger sizes >> >> https://www.transmart.net/current-transformer-cores.html >> >> but the web-site isn't all that transparent, and clearly aimed at >> sophisticated users. > >You ignore simple rule of thumb: energy is more efficiently stored >in air. So to get energy storage needed for critical >damping you need inductor as big or bigger than air cored >inductor. You need core because otherwise winding resistance >is likely be too big for critical damping. > >It seems that inductor with EI core with the following dimensions >could satisfy the needs: > >Surface of the central column: 200 cm^2. >Side of cental column: 14.14 cm. >Height of cental column: 21.21 cm. >Width of winding window: 7.07 cm. >Total height of core: 35.35 cm >Total width of core: 42.42 cm >Total volume of core: 16962.87 cm^3 >Weight of the core: 129426.74 g >Air gap: 1cm > I need that in surface mount. John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
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| From | wmartin <wwm@wwmartin.net> |
|---|---|
| Date | 2026-09-12 21:21 -0700 |
| Message-ID | <11858bq$aknf$1@dont-email.me> |
| In reply to | #747642 |
On 9/12/26 17:59, john larkin wrote: > On Sun, 13 Sep 2026 00:27:24 -0000 (UTC), antispam@fricas.org (Waldek > Hebisch) wrote: > >> Bill Sloman <bill.sloman@ieee.org> wrote: >>> >>> >>> On 10/09/2026 7:10 am, Jeroen Belleman wrote: >>>> On 9/9/26 17:32, Bill Sloman wrote: >>>>> On 9/09/2026 10:25 pm, Jeroen Belleman wrote: >>>>>> On 9/9/26 12:44, john larkin wrote: >>>>>>> On Wed, 9 Sep 2026 09:51:57 -0000 (UTC), piglet >>>>>>> <erichpwagner@hotmail.com> wrote: >>>>>>> >>>>>>>> Bill Sloman <bill.sloman@ieee.org> wrote: >>>>>>>>> On 9/09/2026 5:56 am, john larkin wrote: >>>>>>>>>> On Wed, 9 Sep 2026 03:09:41 +1000, Bill Sloman >>>>>>>>>> <bill.sloman@ieee.org> >>>>>>>>>> wrote: >>>>>>>>>> >>>>>>>>>>> On 9/09/2026 1:00 am, john larkin wrote: >>>>>>>>>>>> On Tue, 8 Sep 2026 17:35:24 +1000, Bill Sloman >>>>>>>>>>>> <bill.sloman@ieee.org> >>>>>>>>>>>> wrote: >>>>>>>>>>>> >>>>>>>>>>>>> On 8/09/2026 4:52 am, john larkin wrote: >>>>>>>>>>>>>> On Mon, 7 Sep 2026 19:33:35 +0100, chrisq >>>>>>>>>>>>>> <syseng@gfsys.co.uk> wrote: >>>>>>>>>>>>>> >>>>>>>>>>>>>>> On 9/7/26 16:18, john larkin wrote: >>>>>>>>>>>>>>>> Suppose we have a box with some big caps inside, for >>>>>>>>>>>>>>>> example 0.2 >>>>>>>>>>>>>>>> farads that run at about 200 volts. When AC power is off, >>>>>>>>>>>>>>>> we want to >>>>>>>>>>>>>>>> discharge them for several reasons. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> Putting, say, a 1K resistor across them dissipates 40 watts >>>>>>>>>>>>>>>> and has a >>>>>>>>>>>>>>>> 200 second time constant. It will take many tau before the >>>>>>>>>>>>>>>> voltage >>>>>>>>>>>>>>>> gets low enough for people to poke around inside. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> The ideal discharger would be a constant-current or even >>>>>>>>>>>>>>>> better a >>>>>>>>>>>>>>>> constant-power load, all the way down to zero volts. It >>>>>>>>>>>>>>>> would be dumb, >>>>>>>>>>>>>>>> not switched by some decision circuit or anything fancy >>>>>>>>>>>>>>>> like that. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> And of course we need several LEDs as warnings that the >>>>>>>>>>>>>>>> thing is hot. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> What sort of design needs 0.2 Farad cap, at 200 volts ?. If >>>>>>>>>>>>>>> you are >>>>>>>>>>>>>>> working at that level, put in a cheap relay and a rated >>>>>>>>>>>>>>> heatsink >>>>>>>>>>>>>>> wirewound resistor to dump the energy, when the power goes off. >>>>>>>>>>>>>>> Cheap, and lossless as well. Motor drive inverters often have >>>>>>>>>>>>>>> big resistors to brake the motor. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> John Larkin >>>>>>>>>>>>>>>> Highland Tech Glen Canyon Design Center >>>>>>>>>>>>>>>> Lunatic Fringe Electronics >>>>>>>>>>>>>> >>>>>>>>>>>>>> It's a 1500 amp laser driver. >>>>>>>>>>>>>> >>>>>>>>>>>>>> The input to our box is DC, from an external power supply. >>>>>>>>>>>>>> >>>>>>>>>>>>>> I do want a circuit that's foolproof, that always discharges >>>>>>>>>>>>>> the caps >>>>>>>>>>>>>> but doen't often go up in flames. >>>>>>>>>>>>>> >>>>>>>>>>>>>> A resistor makes an exponential decay which could be a very >>>>>>>>>>>>>> long time >>>>>>>>>>>>>> to get down to safe levels. >>>>>>>>>>>>> >>>>>>>>>>>>> But a resistor plus an inductor could give a critically damped >>>>>>>>>>>>> decay, >>>>>>>>>>>>> which would be quite a bit faster. I don't know enough about >>>>>>>>>>>>> the circuit >>>>>>>>>>>>> to be prepared to try to work out how much inductance you'd >>>>>>>>>>>>> need, and >>>>>>>>>>>>> you clearly can't be bothered. >>>>>>>>>>>> >>>>>>>>>>>> Won't be bothered. >>>>>>>>>>>> >>>>>>>>>>>>> >>>>>>>>>>>>>> I thought the group might like a circuit design problem once >>>>>>>>>>>>>> in a >>>>>>>>>>>>>> while, a break from politics. >>>>>>>>>>>>> >>>>>>>>>>>>> But you don't do circuit design, and this sort of question >>>>>>>>>>>>> makes it >>>>>>>>>>>>> obvious why you don't. >>>>>>>>>>>> >>>>>>>>>>>> The inductor suggestion is hilarious. Thanks. >>>>>>>>>>> >>>>>>>>>>> It's elementary circuit theory, which you should have been >>>>>>>>>>> taught and I >>>>>>>>>>> had to read about. >>>>>>>>>>> >>>>>>>>>>> If you discharge a capacitor through a resistor, the voltage decays >>>>>>>>>>> exponentially. If you put an inductor in series with the >>>>>>>>>>> resistor the >>>>>>>>>>> voltage decay is a more complicated function of time. If you >>>>>>>>>>> chose the >>>>>>>>>>> resistance and the inductance to create a critically damped >>>>>>>>>>> circuit, the >>>>>>>>>>> voltage across the capacitor will eventually decay more rapidly >>>>>>>>>>> than >>>>>>>>>>> you'd see with just the resistor. >>>>>>>>>>> >>>>>>>>>>> Try reading about Laplace transforms. That's a pretty hilarious >>>>>>>>>>> suggestion to direct at you, but you are the butt of the joke. >>>>>>>>>> >>>>>>>>>> Oh, RLC circuits are no mystery. >>>>>>>>>> >>>>>>>>>> What's funny about the suggestion is the size of the inductor it >>>>>>>>>> would >>>>>>>>>> need. >>>>>>>>> >>>>>>>>> Which you haven't worked out. I spent a few minutes last night >>>>>>>>> trying to >>>>>>>>> work out what I could buy off the shelf from element-14 (the >>>>>>>>> Australian >>>>>>>>> branch of Newark) but their web-site has turned cranky in recent >>>>>>>>> months. >>>>>>>>> >>>>>>>>> The value of the inductance isn't fixed - that and the resistor >>>>>>>>> can be >>>>>>>>> be chosen to get a critically damped LCR, and I figured that I'd >>>>>>>>> start >>>>>>>>> playing with an inductor I could buy. >>>>>>>>> >>>>>>>>> You might end up with a non-progressively wound air-cored toroid. >>>>>>>>> With a >>>>>>>>> 0.2F capacitor the parallel capacitance of the inductor isn't >>>>>>>>> going to >>>>>>>>> be an issue, and the winding resistance could be your damping >>>>>>>>> resistor. >>>>>>>>> >>>>>>>>> 4kJ is a fair bit of energy, but you can get copper quite hot >>>>>>>>> before it >>>>>>>>> explodes. It wouldn't stay hot for long. >>>>>>>>> >>>>>>>> >>>>>>>> I haven’t calculated what ballpark inductance might be required but >>>>>>>> is air >>>>>>>> core even feasible for that? >>>>>>> >>>>>>> If it were about the size of a truck maybe. >>>>>>> >>>>>>> You can estimate the inductance in your head. To discharge 0.2F in, >>>>>>> say 100 seconds, you need 500 ohms. That would of course be the tau of >>>>>>> an exponential decay. Adding an inductor would crisp that up. >>>>>>> >>>>>>> R*C = 100 seconds so we want L/R to be in that ballpark. >>>>> >>>>> 100 seconds is a lot too long from a safety point of view >>>>> >>>>>>> So L is around 50,000 H. >>>>> >>>>> If you start at the wrong end. >>>>> >>>>>>> Check Digikey for that. >>>>>> >>>>>> Critical damping happens when the expression for the impedance of >>>>>> the series RLC has two identical roots. This happens when L = R^2C/4, >>>>>> near enough, so L should be 12.5 kH. >>>>> >>>>> You can vary both L and R. A much shorter time constant means a much >>>>> smaller inductor >>>>> >>>>> I dug out my copy of Grover and thought about a 5H air-cored inductor. >>>>> >>>>> 5H - a 1 sec time constant - would be practicable - but big. You'd >>>>> need a great deal of copper wire to make it work. >>>>> >>>>> It might be worth thinking about an iron-cored inductor. We are >>>>> looking at a fairly slow event so the current induced in the iron >>>>> would be just one more dissipation mode. >>>>> >>>>> 0.5H might work. The time constant of 0.32 sec means that your 4kJ >>>>> looks like 13kW while it is dissipating, but it would be being >>>>> dissipated in what could be a fairly substantial resistor which >>>>> wouldn't warm up much and would have time to cool off. >>>>> >>>>>> With the initial voltage 200V, it will need to briefly store just >>>>>> short of 600 J. That doesn't look like a practical solution. >>>>> >>>>> Why not? Air-cored coils can store a lot of energy. If you put a lot >>>>> of current through the turns the mechanical forces eventually rip them >>>>> apart, but that's a very different regime. >>>>> >>>> >>>> Because an air-core 12.5 kH inductor is *big*. >>> >>> As I managed to work out, after an unfortunate slip of the mind. >>> >>> 12.5KH is much bigger inductance than you would want or need. 100sec to >>> discharge a capacitor is much too long. >>> >>> 5H and and 1sec makes much more sense but the air-cored inductor would >>> still be impractically large. >>> >>> A carbonyl iron core might work >>> >>> https://www.rf-microwave.com/resources/products_attachments/67aa26a4a6d8c.pdf >>> >>> would need 16000 turns of 0.5mm OD copper wire to get to 5H. That's >>> about 34 layers of wire about 2600 metres long, and the series >>> resistance would be 230R, which is too high. >>> >>> 2.5mm OD wire might work, but that's only 100 tuns per layer, and 160 >>> layers would over-fill the winding space. >>> >>> A bigger core could accommodate more turns of thicker wire, but that >>> supplier doesn't do one. >>> >>> An iron tape core would offer more nH per root turn. They are >>> commercially available and in larger sizes >>> >>> https://www.transmart.net/current-transformer-cores.html >>> >>> but the web-site isn't all that transparent, and clearly aimed at >>> sophisticated users. >> >> You ignore simple rule of thumb: energy is more efficiently stored >> in air. So to get energy storage needed for critical >> damping you need inductor as big or bigger than air cored >> inductor. You need core because otherwise winding resistance >> is likely be too big for critical damping. >> >> It seems that inductor with EI core with the following dimensions >> could satisfy the needs: >> >> Surface of the central column: 200 cm^2. >> Side of cental column: 14.14 cm. >> Height of cental column: 21.21 cm. >> Width of winding window: 7.07 cm. >> Total height of core: 35.35 cm >> Total width of core: 42.42 cm >> Total volume of core: 16962.87 cm^3 >> Weight of the core: 129426.74 g >> Air gap: 1cm >> > > I need that in surface mount. > > > John Larkin > Highland Tech Glen Canyon Design Center > Lunatic Fringe Electronics The power companies do that all the time...big box mounted to a concrete slab...surface of the earth mount! :-)
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| From | Bill Sloman <bill.sloman@ieee.org> |
|---|---|
| Date | 2026-09-13 16:27 +1000 |
| Message-ID | <1185fo1$csfm$2@dont-email.me> |
| In reply to | #747642 |
On 13/09/2026 10:59 am, john larkin wrote: > On Sun, 13 Sep 2026 00:27:24 -0000 (UTC), antispam@fricas.org (Waldek > Hebisch) wrote: > >> Bill Sloman <bill.sloman@ieee.org> wrote: >>> >>> >>> On 10/09/2026 7:10 am, Jeroen Belleman wrote: >>>> On 9/9/26 17:32, Bill Sloman wrote: >>>>> On 9/09/2026 10:25 pm, Jeroen Belleman wrote: >>>>>> On 9/9/26 12:44, john larkin wrote: >>>>>>> On Wed, 9 Sep 2026 09:51:57 -0000 (UTC), piglet >>>>>>> <erichpwagner@hotmail.com> wrote: >>>>>>> >>>>>>>> Bill Sloman <bill.sloman@ieee.org> wrote: >>>>>>>>> On 9/09/2026 5:56 am, john larkin wrote: >>>>>>>>>> On Wed, 9 Sep 2026 03:09:41 +1000, Bill Sloman >>>>>>>>>> <bill.sloman@ieee.org> >>>>>>>>>> wrote: >>>>>>>>>> >>>>>>>>>>> On 9/09/2026 1:00 am, john larkin wrote: >>>>>>>>>>>> On Tue, 8 Sep 2026 17:35:24 +1000, Bill Sloman >>>>>>>>>>>> <bill.sloman@ieee.org> >>>>>>>>>>>> wrote: >>>>>>>>>>>> >>>>>>>>>>>>> On 8/09/2026 4:52 am, john larkin wrote: >>>>>>>>>>>>>> On Mon, 7 Sep 2026 19:33:35 +0100, chrisq >>>>>>>>>>>>>> <syseng@gfsys.co.uk> wrote: >>>>>>>>>>>>>> >>>>>>>>>>>>>>> On 9/7/26 16:18, john larkin wrote: >>>>>>>>>>>>>>>> Suppose we have a box with some big caps inside, for >>>>>>>>>>>>>>>> example 0.2 >>>>>>>>>>>>>>>> farads that run at about 200 volts. When AC power is off, >>>>>>>>>>>>>>>> we want to >>>>>>>>>>>>>>>> discharge them for several reasons. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> Putting, say, a 1K resistor across them dissipates 40 watts >>>>>>>>>>>>>>>> and has a >>>>>>>>>>>>>>>> 200 second time constant. It will take many tau before the >>>>>>>>>>>>>>>> voltage >>>>>>>>>>>>>>>> gets low enough for people to poke around inside. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> The ideal discharger would be a constant-current or even >>>>>>>>>>>>>>>> better a >>>>>>>>>>>>>>>> constant-power load, all the way down to zero volts. It >>>>>>>>>>>>>>>> would be dumb, >>>>>>>>>>>>>>>> not switched by some decision circuit or anything fancy >>>>>>>>>>>>>>>> like that. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> And of course we need several LEDs as warnings that the >>>>>>>>>>>>>>>> thing is hot. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> What sort of design needs 0.2 Farad cap, at 200 volts ?. If >>>>>>>>>>>>>>> you are >>>>>>>>>>>>>>> working at that level, put in a cheap relay and a rated >>>>>>>>>>>>>>> heatsink >>>>>>>>>>>>>>> wirewound resistor to dump the energy, when the power goes off. >>>>>>>>>>>>>>> Cheap, and lossless as well. Motor drive inverters often have >>>>>>>>>>>>>>> big resistors to brake the motor. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> John Larkin >>>>>>>>>>>>>>>> Highland Tech Glen Canyon Design Center >>>>>>>>>>>>>>>> Lunatic Fringe Electronics >>>>>>>>>>>>>> >>>>>>>>>>>>>> It's a 1500 amp laser driver. >>>>>>>>>>>>>> >>>>>>>>>>>>>> The input to our box is DC, from an external power supply. >>>>>>>>>>>>>> >>>>>>>>>>>>>> I do want a circuit that's foolproof, that always discharges >>>>>>>>>>>>>> the caps >>>>>>>>>>>>>> but doen't often go up in flames. >>>>>>>>>>>>>> >>>>>>>>>>>>>> A resistor makes an exponential decay which could be a very >>>>>>>>>>>>>> long time >>>>>>>>>>>>>> to get down to safe levels. >>>>>>>>>>>>> >>>>>>>>>>>>> But a resistor plus an inductor could give a critically damped >>>>>>>>>>>>> decay, >>>>>>>>>>>>> which would be quite a bit faster. I don't know enough about >>>>>>>>>>>>> the circuit >>>>>>>>>>>>> to be prepared to try to work out how much inductance you'd >>>>>>>>>>>>> need, and >>>>>>>>>>>>> you clearly can't be bothered. >>>>>>>>>>>> >>>>>>>>>>>> Won't be bothered. >>>>>>>>>>>> >>>>>>>>>>>>> >>>>>>>>>>>>>> I thought the group might like a circuit design problem once >>>>>>>>>>>>>> in a >>>>>>>>>>>>>> while, a break from politics. >>>>>>>>>>>>> >>>>>>>>>>>>> But you don't do circuit design, and this sort of question >>>>>>>>>>>>> makes it >>>>>>>>>>>>> obvious why you don't. >>>>>>>>>>>> >>>>>>>>>>>> The inductor suggestion is hilarious. Thanks. >>>>>>>>>>> >>>>>>>>>>> It's elementary circuit theory, which you should have been >>>>>>>>>>> taught and I >>>>>>>>>>> had to read about. >>>>>>>>>>> >>>>>>>>>>> If you discharge a capacitor through a resistor, the voltage decays >>>>>>>>>>> exponentially. If you put an inductor in series with the >>>>>>>>>>> resistor the >>>>>>>>>>> voltage decay is a more complicated function of time. If you >>>>>>>>>>> chose the >>>>>>>>>>> resistance and the inductance to create a critically damped >>>>>>>>>>> circuit, the >>>>>>>>>>> voltage across the capacitor will eventually decay more rapidly >>>>>>>>>>> than >>>>>>>>>>> you'd see with just the resistor. >>>>>>>>>>> >>>>>>>>>>> Try reading about Laplace transforms. That's a pretty hilarious >>>>>>>>>>> suggestion to direct at you, but you are the butt of the joke. >>>>>>>>>> >>>>>>>>>> Oh, RLC circuits are no mystery. >>>>>>>>>> >>>>>>>>>> What's funny about the suggestion is the size of the inductor it >>>>>>>>>> would >>>>>>>>>> need. >>>>>>>>> >>>>>>>>> Which you haven't worked out. I spent a few minutes last night >>>>>>>>> trying to >>>>>>>>> work out what I could buy off the shelf from element-14 (the >>>>>>>>> Australian >>>>>>>>> branch of Newark) but their web-site has turned cranky in recent >>>>>>>>> months. >>>>>>>>> >>>>>>>>> The value of the inductance isn't fixed - that and the resistor >>>>>>>>> can be >>>>>>>>> be chosen to get a critically damped LCR, and I figured that I'd >>>>>>>>> start >>>>>>>>> playing with an inductor I could buy. >>>>>>>>> >>>>>>>>> You might end up with a non-progressively wound air-cored toroid. >>>>>>>>> With a >>>>>>>>> 0.2F capacitor the parallel capacitance of the inductor isn't >>>>>>>>> going to >>>>>>>>> be an issue, and the winding resistance could be your damping >>>>>>>>> resistor. >>>>>>>>> >>>>>>>>> 4kJ is a fair bit of energy, but you can get copper quite hot >>>>>>>>> before it >>>>>>>>> explodes. It wouldn't stay hot for long. >>>>>>>>> >>>>>>>> >>>>>>>> I haven’t calculated what ballpark inductance might be required but >>>>>>>> is air >>>>>>>> core even feasible for that? >>>>>>> >>>>>>> If it were about the size of a truck maybe. >>>>>>> >>>>>>> You can estimate the inductance in your head. To discharge 0.2F in, >>>>>>> say 100 seconds, you need 500 ohms. That would of course be the tau of >>>>>>> an exponential decay. Adding an inductor would crisp that up. >>>>>>> >>>>>>> R*C = 100 seconds so we want L/R to be in that ballpark. >>>>> >>>>> 100 seconds is a lot too long from a safety point of view >>>>> >>>>>>> So L is around 50,000 H. >>>>> >>>>> If you start at the wrong end. >>>>> >>>>>>> Check Digikey for that. >>>>>> >>>>>> Critical damping happens when the expression for the impedance of >>>>>> the series RLC has two identical roots. This happens when L = R^2C/4, >>>>>> near enough, so L should be 12.5 kH. >>>>> >>>>> You can vary both L and R. A much shorter time constant means a much >>>>> smaller inductor >>>>> >>>>> I dug out my copy of Grover and thought about a 5H air-cored inductor. >>>>> >>>>> 5H - a 1 sec time constant - would be practicable - but big. You'd >>>>> need a great deal of copper wire to make it work. >>>>> >>>>> It might be worth thinking about an iron-cored inductor. We are >>>>> looking at a fairly slow event so the current induced in the iron >>>>> would be just one more dissipation mode. >>>>> >>>>> 0.5H might work. The time constant of 0.32 sec means that your 4kJ >>>>> looks like 13kW while it is dissipating, but it would be being >>>>> dissipated in what could be a fairly substantial resistor which >>>>> wouldn't warm up much and would have time to cool off. >>>>> >>>>>> With the initial voltage 200V, it will need to briefly store just >>>>>> short of 600 J. That doesn't look like a practical solution. >>>>> >>>>> Why not? Air-cored coils can store a lot of energy. If you put a lot >>>>> of current through the turns the mechanical forces eventually rip them >>>>> apart, but that's a very different regime. >>>>> >>>> >>>> Because an air-core 12.5 kH inductor is *big*. >>> >>> As I managed to work out, after an unfortunate slip of the mind. >>> >>> 12.5KH is much bigger inductance than you would want or need. 100sec to >>> discharge a capacitor is much too long. >>> >>> 5H and and 1sec makes much more sense but the air-cored inductor would >>> still be impractically large. >>> >>> A carbonyl iron core might work >>> >>> https://www.rf-microwave.com/resources/products_attachments/67aa26a4a6d8c.pdf >>> >>> would need 16000 turns of 0.5mm OD copper wire to get to 5H. That's >>> about 34 layers of wire about 2600 metres long, and the series >>> resistance would be 230R, which is too high. >>> >>> 2.5mm OD wire might work, but that's only 100 tuns per layer, and 160 >>> layers would over-fill the winding space. >>> >>> A bigger core could accommodate more turns of thicker wire, but that >>> supplier doesn't do one. >>> >>> An iron tape core would offer more nH per root turn. They are >>> commercially available and in larger sizes >>> >>> https://www.transmart.net/current-transformer-cores.html >>> >>> but the web-site isn't all that transparent, and clearly aimed at >>> sophisticated users. >> >> You ignore simple rule of thumb: energy is more efficiently stored >> in air. So to get energy storage needed for critical >> damping you need inductor as big or bigger than air cored >> inductor. You need core because otherwise winding resistance >> is likely be too big for critical damping. >> >> It seems that inductor with EI core with the following dimensions >> could satisfy the needs: >> >> Surface of the central column: 200 cm^2. >> Side of cental column: 14.14 cm. >> Height of cental column: 21.21 cm. >> Width of winding window: 7.07 cm. >> Total height of core: 35.35 cm >> Total width of core: 42.42 cm >> Total volume of core: 16962.87 cm^3 >> Weight of the core: 129426.74 g >> Air gap: 1cm >> > > I need that in surface mount. Just like the capacitor? -- Bill Sloman, Sydney
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| From | Bill Sloman <bill.sloman@ieee.org> |
|---|---|
| Date | 2026-09-13 16:24 +1000 |
| Message-ID | <1185fji$csfm$1@dont-email.me> |
| In reply to | #747637 |
On 13/09/2026 10:27 am, Waldek Hebisch wrote: > Bill Sloman <bill.sloman@ieee.org> wrote: >> >> >> On 10/09/2026 7:10 am, Jeroen Belleman wrote: >>> On 9/9/26 17:32, Bill Sloman wrote: >>>> On 9/09/2026 10:25 pm, Jeroen Belleman wrote: >>>>> On 9/9/26 12:44, john larkin wrote: >>>>>> On Wed, 9 Sep 2026 09:51:57 -0000 (UTC), piglet >>>>>> <erichpwagner@hotmail.com> wrote: >>>>>> >>>>>>> Bill Sloman <bill.sloman@ieee.org> wrote: >>>>>>>> On 9/09/2026 5:56 am, john larkin wrote: >>>>>>>>> On Wed, 9 Sep 2026 03:09:41 +1000, Bill Sloman >>>>>>>>> <bill.sloman@ieee.org> >>>>>>>>> wrote: >>>>>>>>> >>>>>>>>>> On 9/09/2026 1:00 am, john larkin wrote: >>>>>>>>>>> On Tue, 8 Sep 2026 17:35:24 +1000, Bill Sloman >>>>>>>>>>> <bill.sloman@ieee.org> >>>>>>>>>>> wrote: >>>>>>>>>>> >>>>>>>>>>>> On 8/09/2026 4:52 am, john larkin wrote: >>>>>>>>>>>>> On Mon, 7 Sep 2026 19:33:35 +0100, chrisq >>>>>>>>>>>>> <syseng@gfsys.co.uk> wrote: >>>>>>>>>>>>> >>>>>>>>>>>>>> On 9/7/26 16:18, john larkin wrote: >>>>>>>>>>>>>>> Suppose we have a box with some big caps inside, for >>>>>>>>>>>>>>> example 0.2 >>>>>>>>>>>>>>> farads that run at about 200 volts. When AC power is off, >>>>>>>>>>>>>>> we want to >>>>>>>>>>>>>>> discharge them for several reasons. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Putting, say, a 1K resistor across them dissipates 40 watts >>>>>>>>>>>>>>> and has a >>>>>>>>>>>>>>> 200 second time constant. It will take many tau before the >>>>>>>>>>>>>>> voltage >>>>>>>>>>>>>>> gets low enough for people to poke around inside. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> The ideal discharger would be a constant-current or even >>>>>>>>>>>>>>> better a >>>>>>>>>>>>>>> constant-power load, all the way down to zero volts. It >>>>>>>>>>>>>>> would be dumb, >>>>>>>>>>>>>>> not switched by some decision circuit or anything fancy >>>>>>>>>>>>>>> like that. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> And of course we need several LEDs as warnings that the >>>>>>>>>>>>>>> thing is hot. >>>>>>>>>>>>>>> >>>>>>>>>>>>>> >>>>>>>>>>>>>> What sort of design needs 0.2 Farad cap, at 200 volts ?. If >>>>>>>>>>>>>> you are >>>>>>>>>>>>>> working at that level, put in a cheap relay and a rated >>>>>>>>>>>>>> heatsink >>>>>>>>>>>>>> wirewound resistor to dump the energy, when the power goes off. >>>>>>>>>>>>>> Cheap, and lossless as well. Motor drive inverters often have >>>>>>>>>>>>>> big resistors to brake the motor. >>>>>>>>>>>>>> >>>>>>>>>>>>>> >>>>>>>>>>>>>>> John Larkin >>>>>>>>>>>>>>> Highland Tech Glen Canyon Design Center >>>>>>>>>>>>>>> Lunatic Fringe Electronics >>>>>>>>>>>>> >>>>>>>>>>>>> It's a 1500 amp laser driver. >>>>>>>>>>>>> >>>>>>>>>>>>> The input to our box is DC, from an external power supply. >>>>>>>>>>>>> >>>>>>>>>>>>> I do want a circuit that's foolproof, that always discharges >>>>>>>>>>>>> the caps >>>>>>>>>>>>> but doen't often go up in flames. >>>>>>>>>>>>> >>>>>>>>>>>>> A resistor makes an exponential decay which could be a very >>>>>>>>>>>>> long time >>>>>>>>>>>>> to get down to safe levels. >>>>>>>>>>>> >>>>>>>>>>>> But a resistor plus an inductor could give a critically damped >>>>>>>>>>>> decay, >>>>>>>>>>>> which would be quite a bit faster. I don't know enough about >>>>>>>>>>>> the circuit >>>>>>>>>>>> to be prepared to try to work out how much inductance you'd >>>>>>>>>>>> need, and >>>>>>>>>>>> you clearly can't be bothered. >>>>>>>>>>> >>>>>>>>>>> Won't be bothered. >>>>>>>>>>> >>>>>>>>>>>> >>>>>>>>>>>>> I thought the group might like a circuit design problem once >>>>>>>>>>>>> in a >>>>>>>>>>>>> while, a break from politics. >>>>>>>>>>>> >>>>>>>>>>>> But you don't do circuit design, and this sort of question >>>>>>>>>>>> makes it >>>>>>>>>>>> obvious why you don't. >>>>>>>>>>> >>>>>>>>>>> The inductor suggestion is hilarious. Thanks. >>>>>>>>>> >>>>>>>>>> It's elementary circuit theory, which you should have been >>>>>>>>>> taught and I >>>>>>>>>> had to read about. >>>>>>>>>> >>>>>>>>>> If you discharge a capacitor through a resistor, the voltage decays >>>>>>>>>> exponentially. If you put an inductor in series with the >>>>>>>>>> resistor the >>>>>>>>>> voltage decay is a more complicated function of time. If you >>>>>>>>>> chose the >>>>>>>>>> resistance and the inductance to create a critically damped >>>>>>>>>> circuit, the >>>>>>>>>> voltage across the capacitor will eventually decay more rapidly >>>>>>>>>> than >>>>>>>>>> you'd see with just the resistor. >>>>>>>>>> >>>>>>>>>> Try reading about Laplace transforms. That's a pretty hilarious >>>>>>>>>> suggestion to direct at you, but you are the butt of the joke. >>>>>>>>> >>>>>>>>> Oh, RLC circuits are no mystery. >>>>>>>>> >>>>>>>>> What's funny about the suggestion is the size of the inductor it >>>>>>>>> would >>>>>>>>> need. >>>>>>>> >>>>>>>> Which you haven't worked out. I spent a few minutes last night >>>>>>>> trying to >>>>>>>> work out what I could buy off the shelf from element-14 (the >>>>>>>> Australian >>>>>>>> branch of Newark) but their web-site has turned cranky in recent >>>>>>>> months. >>>>>>>> >>>>>>>> The value of the inductance isn't fixed - that and the resistor >>>>>>>> can be >>>>>>>> be chosen to get a critically damped LCR, and I figured that I'd >>>>>>>> start >>>>>>>> playing with an inductor I could buy. >>>>>>>> >>>>>>>> You might end up with a non-progressively wound air-cored toroid. >>>>>>>> With a >>>>>>>> 0.2F capacitor the parallel capacitance of the inductor isn't >>>>>>>> going to >>>>>>>> be an issue, and the winding resistance could be your damping >>>>>>>> resistor. >>>>>>>> >>>>>>>> 4kJ is a fair bit of energy, but you can get copper quite hot >>>>>>>> before it >>>>>>>> explodes. It wouldn't stay hot for long. >>>>>>>> >>>>>>> >>>>>>> I haven’t calculated what ballpark inductance might be required but >>>>>>> is air >>>>>>> core even feasible for that? >>>>>> >>>>>> If it were about the size of a truck maybe. >>>>>> >>>>>> You can estimate the inductance in your head. To discharge 0.2F in, >>>>>> say 100 seconds, you need 500 ohms. That would of course be the tau of >>>>>> an exponential decay. Adding an inductor would crisp that up. >>>>>> >>>>>> R*C = 100 seconds so we want L/R to be in that ballpark. >>>> >>>> 100 seconds is a lot too long from a safety point of view >>>> >>>>>> So L is around 50,000 H. >>>> >>>> If you start at the wrong end. >>>> >>>>>> Check Digikey for that. >>>>> >>>>> Critical damping happens when the expression for the impedance of >>>>> the series RLC has two identical roots. This happens when L = R^2C/4, >>>>> near enough, so L should be 12.5 kH. >>>> >>>> You can vary both L and R. A much shorter time constant means a much >>>> smaller inductor >>>> >>>> I dug out my copy of Grover and thought about a 5H air-cored inductor. >>>> >>>> 5H - a 1 sec time constant - would be practicable - but big. You'd >>>> need a great deal of copper wire to make it work. >>>> >>>> It might be worth thinking about an iron-cored inductor. We are >>>> looking at a fairly slow event so the current induced in the iron >>>> would be just one more dissipation mode. >>>> >>>> 0.5H might work. The time constant of 0.32 sec means that your 4kJ >>>> looks like 13kW while it is dissipating, but it would be being >>>> dissipated in what could be a fairly substantial resistor which >>>> wouldn't warm up much and would have time to cool off. >>>> >>>>> With the initial voltage 200V, it will need to briefly store just >>>>> short of 600 J. That doesn't look like a practical solution. >>>> >>>> Why not? Air-cored coils can store a lot of energy. If you put a lot >>>> of current through the turns the mechanical forces eventually rip them >>>> apart, but that's a very different regime. >>>> >>> >>> Because an air-core 12.5 kH inductor is *big*. >> >> As I managed to work out, after an unfortunate slip of the mind. >> >> 12.5KH is much bigger inductance than you would want or need. 100sec to >> discharge a capacitor is much too long. >> >> 5H and and 1sec makes much more sense but the air-cored inductor would >> still be impractically large. >> >> A carbonyl iron core might work >> >> https://www.rf-microwave.com/resources/products_attachments/67aa26a4a6d8c.pdf >> >> would need 16000 turns of 0.5mm OD copper wire to get to 5H. That's >> about 34 layers of wire about 2600 metres long, and the series >> resistance would be 230R, which is too high. >> >> 2.5mm OD wire might work, but that's only 100 tuns per layer, and 160 >> layers would over-fill the winding space. >> >> A bigger core could accommodate more turns of thicker wire, but that >> supplier doesn't do one. >> >> An iron tape core would offer more nH per root turn. They are >> commercially available and in larger sizes >> >> https://www.transmart.net/current-transformer-cores.html >> >> but the web-site isn't all that transparent, and clearly aimed at >> sophisticated users. > > You ignore simple rule of thumb: energy is more efficiently stored > in air. Efficiency is just the ratio of your solution to an ideal solution. You haven't indicated what you are comparing. Energy is more simply stored in an iron cored inductor because can get a higher inductance in a given volume - the iron eventually saturates which complicates life, and the iron would act as a shorted turn if you gave it half a chance. > So to get energy storage needed for critical > damping you need inductor as big or bigger than air cored > inductor. That doesn't follow. > You need core because otherwise winding resistance > is likely be too big for critical damping. We can all dream of superconducting wire, but all the versions I know of stop being super-conducting at a high enough magnetic field. I once got to clamber around the Nijmegen University's super-conducting magnet so I know that that can be a pretty high field. > > It seems that inductor with EI core with the following dimensions > could satisfy the needs: > > Surface of the central column: 200 cm^2. > Side of cental column: 14.14 cm. > Height of cental column: 21.21 cm. > Width of winding window: 7.07 cm. > Total height of core: 35.35 cm > Total width of core: 42.42 cm > Total volume of core: 16962.87 cm^3 > Weight of the core: 129426.74 g > Air gap: 1cm You haven't specified the core material. My guess is that you would have to glom it together from rectangular lumps of ferrite. With that much air-gap, the exact material wouldn't matter much. https://product.tdk.com/ lists a bunch. > To get L = 5H needs 1727 turns. I get 1.43 Ohm as winding resistance. > > So I guess that if one really needed such an inductor it would > be practical. But it is bulky. I am not sure if it is bigger > than the capacitor bank, but I expect it to be heavier. I'd be more interested in a toroidial core wound out of iron ribbon. https://megatron.ch/en/produkt-kategorie/ringbandkerne-und-schnittbandkerne/ Even with a high permeability (layered) iron core you'd still need quite a few turns to get a Henry or so of inductance. The data sheets aren't exactly helpful. https://megatron.ch/infocenter/AMCC_100_Datenblatt.pdf -- Bill Sloman. Sydney
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| From | antispam@fricas.org (Waldek Hebisch) |
|---|---|
| Date | 2026-09-13 13:36 +0000 |
| Message-ID | <11868rv$1260e$1@paganini.bofh.team> |
| In reply to | #747649 |
Bill Sloman <bill.sloman@ieee.org> wrote:
> On 13/09/2026 10:27 am, Waldek Hebisch wrote:
>> Bill Sloman <bill.sloman@ieee.org> wrote:
>>>
>>>
>>> On 10/09/2026 7:10 am, Jeroen Belleman wrote:
>>>> On 9/9/26 17:32, Bill Sloman wrote:
>>>>> On 9/09/2026 10:25 pm, Jeroen Belleman wrote:
>>>>>> On 9/9/26 12:44, john larkin wrote:
>>>>>>> On Wed, 9 Sep 2026 09:51:57 -0000 (UTC), piglet
>>>>>>> <erichpwagner@hotmail.com> wrote:
>>>>>>>
>>>>>>>> Bill Sloman <bill.sloman@ieee.org> wrote:
>>>>>>>>> On 9/09/2026 5:56 am, john larkin wrote:
>>>>>>>>>> On Wed, 9 Sep 2026 03:09:41 +1000, Bill Sloman
>>>>>>>>>> <bill.sloman@ieee.org>
>>>>>>>>>> wrote:
>>>>>>>>>>
>>>>>>>>>>> On 9/09/2026 1:00 am, john larkin wrote:
>>>>>>>>>>>> On Tue, 8 Sep 2026 17:35:24 +1000, Bill Sloman
>>>>>>>>>>>> <bill.sloman@ieee.org>
>>>>>>>>>>>> wrote:
>>>>>>>>>>>>
>>>>>>>>>>>>> On 8/09/2026 4:52 am, john larkin wrote:
>>>>>>>>>>>>>> On Mon, 7 Sep 2026 19:33:35 +0100, chrisq
>>>>>>>>>>>>>> <syseng@gfsys.co.uk> wrote:
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> On 9/7/26 16:18, john larkin wrote:
>>>>>>>>>>>>>>>> Suppose we have a box with some big caps inside, for
>>>>>>>>>>>>>>>> example 0.2
>>>>>>>>>>>>>>>> farads that run at about 200 volts. When AC power is off,
>>>>>>>>>>>>>>>> we want to
>>>>>>>>>>>>>>>> discharge them for several reasons.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> Putting, say, a 1K resistor across them dissipates 40 watts
>>>>>>>>>>>>>>>> and has a
>>>>>>>>>>>>>>>> 200 second time constant. It will take many tau before the
>>>>>>>>>>>>>>>> voltage
>>>>>>>>>>>>>>>> gets low enough for people to poke around inside.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> The ideal discharger would be a constant-current or even
>>>>>>>>>>>>>>>> better a
>>>>>>>>>>>>>>>> constant-power load, all the way down to zero volts. It
>>>>>>>>>>>>>>>> would be dumb,
>>>>>>>>>>>>>>>> not switched by some decision circuit or anything fancy
>>>>>>>>>>>>>>>> like that.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> And of course we need several LEDs as warnings that the
>>>>>>>>>>>>>>>> thing is hot.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> What sort of design needs 0.2 Farad cap, at 200 volts ?. If
>>>>>>>>>>>>>>> you are
>>>>>>>>>>>>>>> working at that level, put in a cheap relay and a rated
>>>>>>>>>>>>>>> heatsink
>>>>>>>>>>>>>>> wirewound resistor to dump the energy, when the power goes off.
>>>>>>>>>>>>>>> Cheap, and lossless as well. Motor drive inverters often have
>>>>>>>>>>>>>>> big resistors to brake the motor.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> John Larkin
>>>>>>>>>>>>>>>> Highland Tech Glen Canyon Design Center
>>>>>>>>>>>>>>>> Lunatic Fringe Electronics
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> It's a 1500 amp laser driver.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> The input to our box is DC, from an external power supply.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> I do want a circuit that's foolproof, that always discharges
>>>>>>>>>>>>>> the caps
>>>>>>>>>>>>>> but doen't often go up in flames.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> A resistor makes an exponential decay which could be a very
>>>>>>>>>>>>>> long time
>>>>>>>>>>>>>> to get down to safe levels.
>>>>>>>>>>>>>
>>>>>>>>>>>>> But a resistor plus an inductor could give a critically damped
>>>>>>>>>>>>> decay,
>>>>>>>>>>>>> which would be quite a bit faster. I don't know enough about
>>>>>>>>>>>>> the circuit
>>>>>>>>>>>>> to be prepared to try to work out how much inductance you'd
>>>>>>>>>>>>> need, and
>>>>>>>>>>>>> you clearly can't be bothered.
>>>>>>>>>>>>
>>>>>>>>>>>> Won't be bothered.
>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>> I thought the group might like a circuit design problem once
>>>>>>>>>>>>>> in a
>>>>>>>>>>>>>> while, a break from politics.
>>>>>>>>>>>>>
>>>>>>>>>>>>> But you don't do circuit design, and this sort of question
>>>>>>>>>>>>> makes it
>>>>>>>>>>>>> obvious why you don't.
>>>>>>>>>>>>
>>>>>>>>>>>> The inductor suggestion is hilarious. Thanks.
>>>>>>>>>>>
>>>>>>>>>>> It's elementary circuit theory, which you should have been
>>>>>>>>>>> taught and I
>>>>>>>>>>> had to read about.
>>>>>>>>>>>
>>>>>>>>>>> If you discharge a capacitor through a resistor, the voltage decays
>>>>>>>>>>> exponentially. If you put an inductor in series with the
>>>>>>>>>>> resistor the
>>>>>>>>>>> voltage decay is a more complicated function of time. If you
>>>>>>>>>>> chose the
>>>>>>>>>>> resistance and the inductance to create a critically damped
>>>>>>>>>>> circuit, the
>>>>>>>>>>> voltage across the capacitor will eventually decay more rapidly
>>>>>>>>>>> than
>>>>>>>>>>> you'd see with just the resistor.
>>>>>>>>>>>
>>>>>>>>>>> Try reading about Laplace transforms. That's a pretty hilarious
>>>>>>>>>>> suggestion to direct at you, but you are the butt of the joke.
>>>>>>>>>>
>>>>>>>>>> Oh, RLC circuits are no mystery.
>>>>>>>>>>
>>>>>>>>>> What's funny about the suggestion is the size of the inductor it
>>>>>>>>>> would
>>>>>>>>>> need.
>>>>>>>>>
>>>>>>>>> Which you haven't worked out. I spent a few minutes last night
>>>>>>>>> trying to
>>>>>>>>> work out what I could buy off the shelf from element-14 (the
>>>>>>>>> Australian
>>>>>>>>> branch of Newark) but their web-site has turned cranky in recent
>>>>>>>>> months.
>>>>>>>>>
>>>>>>>>> The value of the inductance isn't fixed - that and the resistor
>>>>>>>>> can be
>>>>>>>>> be chosen to get a critically damped LCR, and I figured that I'd
>>>>>>>>> start
>>>>>>>>> playing with an inductor I could buy.
>>>>>>>>>
>>>>>>>>> You might end up with a non-progressively wound air-cored toroid.
>>>>>>>>> With a
>>>>>>>>> 0.2F capacitor the parallel capacitance of the inductor isn't
>>>>>>>>> going to
>>>>>>>>> be an issue, and the winding resistance could be your damping
>>>>>>>>> resistor.
>>>>>>>>>
>>>>>>>>> 4kJ is a fair bit of energy, but you can get copper quite hot
>>>>>>>>> before it
>>>>>>>>> explodes. It wouldn't stay hot for long.
>>>>>>>>>
>>>>>>>>
>>>>>>>> I haven’t calculated what ballpark inductance might be required but
>>>>>>>> is air
>>>>>>>> core even feasible for that?
>>>>>>>
>>>>>>> If it were about the size of a truck maybe.
>>>>>>>
>>>>>>> You can estimate the inductance in your head. To discharge 0.2F in,
>>>>>>> say 100 seconds, you need 500 ohms. That would of course be the tau of
>>>>>>> an exponential decay. Adding an inductor would crisp that up.
>>>>>>>
>>>>>>> R*C = 100 seconds so we want L/R to be in that ballpark.
>>>>>
>>>>> 100 seconds is a lot too long from a safety point of view
>>>>>
>>>>>>> So L is around 50,000 H.
>>>>>
>>>>> If you start at the wrong end.
>>>>>
>>>>>>> Check Digikey for that.
>>>>>>
>>>>>> Critical damping happens when the expression for the impedance of
>>>>>> the series RLC has two identical roots. This happens when L = R^2C/4,
>>>>>> near enough, so L should be 12.5 kH.
>>>>>
>>>>> You can vary both L and R. A much shorter time constant means a much
>>>>> smaller inductor
>>>>>
>>>>> I dug out my copy of Grover and thought about a 5H air-cored inductor.
>>>>>
>>>>> 5H - a 1 sec time constant - would be practicable - but big. You'd
>>>>> need a great deal of copper wire to make it work.
>>>>>
>>>>> It might be worth thinking about an iron-cored inductor. We are
>>>>> looking at a fairly slow event so the current induced in the iron
>>>>> would be just one more dissipation mode.
>>>>>
>>>>> 0.5H might work. The time constant of 0.32 sec means that your 4kJ
>>>>> looks like 13kW while it is dissipating, but it would be being
>>>>> dissipated in what could be a fairly substantial resistor which
>>>>> wouldn't warm up much and would have time to cool off.
>>>>>
>>>>>> With the initial voltage 200V, it will need to briefly store just
>>>>>> short of 600 J. That doesn't look like a practical solution.
>>>>>
>>>>> Why not? Air-cored coils can store a lot of energy. If you put a lot
>>>>> of current through the turns the mechanical forces eventually rip them
>>>>> apart, but that's a very different regime.
>>>>>
>>>>
>>>> Because an air-core 12.5 kH inductor is *big*.
>>>
>>> As I managed to work out, after an unfortunate slip of the mind.
>>>
>>> 12.5KH is much bigger inductance than you would want or need. 100sec to
>>> discharge a capacitor is much too long.
>>>
>>> 5H and and 1sec makes much more sense but the air-cored inductor would
>>> still be impractically large.
>>>
>>> A carbonyl iron core might work
>>>
>>> https://www.rf-microwave.com/resources/products_attachments/67aa26a4a6d8c.pdf
>>>
>>> would need 16000 turns of 0.5mm OD copper wire to get to 5H. That's
>>> about 34 layers of wire about 2600 metres long, and the series
>>> resistance would be 230R, which is too high.
>>>
>>> 2.5mm OD wire might work, but that's only 100 tuns per layer, and 160
>>> layers would over-fill the winding space.
>>>
>>> A bigger core could accommodate more turns of thicker wire, but that
>>> supplier doesn't do one.
>>>
>>> An iron tape core would offer more nH per root turn. They are
>>> commercially available and in larger sizes
>>>
>>> https://www.transmart.net/current-transformer-cores.html
>>>
>>> but the web-site isn't all that transparent, and clearly aimed at
>>> sophisticated users.
>>
>> You ignore simple rule of thumb: energy is more efficiently stored
>> in air.
>
> Efficiency is just the ratio of your solution to an ideal solution.
>
> You haven't indicated what you are comparing.
>
> Energy is more simply stored in an iron cored inductor because can get a
> higher inductance in a given volume - the iron eventually saturates
> which complicates life, and the iron would act as a shorted turn if you
> gave it half a chance.
Approximate formula for maximal energy stored in inductor with a gap is:
E = S*B_max^2*(l_i/mu + l_g)/(2*\mu_0)
where E is the energy, B_max is maximal possible induction in the core,
S is surface area of the perpendicular cut trough the core, l_i is
average length of magnetic path in the core, l_g is effective path
trough the gap, \mu is relative magnetic permeability of the core,
\mu_0 is magnetic permeability of the vacuum.
The formula above assumes that you can pass whatever current is
needed trough the winding and the only limit to current is due to
core saturation. As you can see better magnetic permeability
_decreases_ maximal possible energy, simply core will saturate
at lower current and gap significantly increases possible energy
storage.
For comparison, formula for inductance is:
L = N^2*S*\mu_0/(l_i/\mu + l_g)
where N is number of turns and the other are as above. So design
for high energy will by neccessity have lower inductance. Winding
resistance is proportional to N^2, so if you need higher ratio
of inductance to resistance you need to go for bigger inductor
or lower stored energy.
>> So to get energy storage needed for critical
>> damping you need inductor as big or bigger than air cored
>> inductor.
>
> That doesn't follow.
The formula above shows this clearly: removing core allows
bigger B and increases l_g term. Of course, once gap it
too big approximation is rather poor, but trend is clear.
>> You need core because otherwise winding resistance
>> is likely be too big for critical damping.
>
> We can all dream of superconducting wire, but all the versions I know of
> stop being super-conducting at a high enough magnetic field. I once got
> to clamber around the Nijmegen University's super-conducting magnet so I
> know that that can be a pretty high field.
Yes. And we dream of superconducting wire which needs no refrigeration.
>> It seems that inductor with EI core with the following dimensions
>> could satisfy the needs:
>>
>> Surface of the central column: 200 cm^2.
>> Side of cental column: 14.14 cm.
>> Height of cental column: 21.21 cm.
>> Width of winding window: 7.07 cm.
>> Total height of core: 35.35 cm
>> Total width of core: 42.42 cm
>> Total volume of core: 16962.87 cm^3
>> Weight of the core: 129426.74 g
>> Air gap: 1cm
>
> You haven't specified the core material. My guess is that you would have
> to glom it together from rectangular lumps of ferrite. With that much
> air-gap, the exact material wouldn't matter much.
I assumed iron. What matter is maximal allowed induction. Actually
AFAICS going slightly into saturation does not hurt, so I assumend
operation slightly above normal limits.
> https://product.tdk.com/
>
> lists a bunch.
>
>> To get L = 5H needs 1727 turns. I get 1.43 Ohm as winding resistance.
>>
>> So I guess that if one really needed such an inductor it would
>> be practical. But it is bulky. I am not sure if it is bigger
>> than the capacitor bank, but I expect it to be heavier.
>
> I'd be more interested in a toroidial core wound out of iron ribbon.
>
> https://megatron.ch/en/produkt-kategorie/ringbandkerne-und-schnittbandkerne/
>
> Even with a high permeability (layered) iron core you'd still need quite
> a few turns to get a Henry or so of inductance.
As I explained, main trouble is core saturation. The approximate
formula applies to toroids too.
> The data sheets aren't exactly helpful.
>
> https://megatron.ch/infocenter/AMCC_100_Datenblatt.pdf
>
--
Waldek Hebisch
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| From | Bill Sloman <bill.sloman@ieee.org> |
|---|---|
| Date | 2026-09-14 02:05 +1000 |
| Message-ID | <1186hjn$oig9$1@dont-email.me> |
| In reply to | #747658 |
On 13/09/2026 11:36 pm, Waldek Hebisch wrote: > Bill Sloman <bill.sloman@ieee.org> wrote: >> On 13/09/2026 10:27 am, Waldek Hebisch wrote: >>> Bill Sloman <bill.sloman@ieee.org> wrote: >>>> >>>> >>>> On 10/09/2026 7:10 am, Jeroen Belleman wrote: >>>>> On 9/9/26 17:32, Bill Sloman wrote: >>>>>> On 9/09/2026 10:25 pm, Jeroen Belleman wrote: >>>>>>> On 9/9/26 12:44, john larkin wrote: >>>>>>>> On Wed, 9 Sep 2026 09:51:57 -0000 (UTC), piglet >>>>>>>> <erichpwagner@hotmail.com> wrote: >>>>>>>> >>>>>>>>> Bill Sloman <bill.sloman@ieee.org> wrote: >>>>>>>>>> On 9/09/2026 5:56 am, john larkin wrote: >>>>>>>>>>> On Wed, 9 Sep 2026 03:09:41 +1000, Bill Sloman >>>>>>>>>>> <bill.sloman@ieee.org> >>>>>>>>>>> wrote: >>>>>>>>>>> >>>>>>>>>>>> On 9/09/2026 1:00 am, john larkin wrote: >>>>>>>>>>>>> On Tue, 8 Sep 2026 17:35:24 +1000, Bill Sloman >>>>>>>>>>>>> <bill.sloman@ieee.org> >>>>>>>>>>>>> wrote: >>>>>>>>>>>>> >>>>>>>>>>>>>> On 8/09/2026 4:52 am, john larkin wrote: >>>>>>>>>>>>>>> On Mon, 7 Sep 2026 19:33:35 +0100, chrisq >>>>>>>>>>>>>>> <syseng@gfsys.co.uk> wrote: >>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> On 9/7/26 16:18, john larkin wrote: >>>>>>>>>>>>>>>>> Suppose we have a box with some big caps inside, for >>>>>>>>>>>>>>>>> example 0.2 >>>>>>>>>>>>>>>>> farads that run at about 200 volts. When AC power is off, >>>>>>>>>>>>>>>>> we want to >>>>>>>>>>>>>>>>> discharge them for several reasons. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> Putting, say, a 1K resistor across them dissipates 40 watts >>>>>>>>>>>>>>>>> and has a >>>>>>>>>>>>>>>>> 200 second time constant. It will take many tau before the >>>>>>>>>>>>>>>>> voltage >>>>>>>>>>>>>>>>> gets low enough for people to poke around inside. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> The ideal discharger would be a constant-current or even >>>>>>>>>>>>>>>>> better a >>>>>>>>>>>>>>>>> constant-power load, all the way down to zero volts. It >>>>>>>>>>>>>>>>> would be dumb, >>>>>>>>>>>>>>>>> not switched by some decision circuit or anything fancy >>>>>>>>>>>>>>>>> like that. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> And of course we need several LEDs as warnings that the >>>>>>>>>>>>>>>>> thing is hot. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> What sort of design needs 0.2 Farad cap, at 200 volts ?. If >>>>>>>>>>>>>>>> you are >>>>>>>>>>>>>>>> working at that level, put in a cheap relay and a rated >>>>>>>>>>>>>>>> heatsink >>>>>>>>>>>>>>>> wirewound resistor to dump the energy, when the power goes off. >>>>>>>>>>>>>>>> Cheap, and lossless as well. Motor drive inverters often have >>>>>>>>>>>>>>>> big resistors to brake the motor. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> John Larkin >>>>>>>>>>>>>>>>> Highland Tech Glen Canyon Design Center >>>>>>>>>>>>>>>>> Lunatic Fringe Electronics >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> It's a 1500 amp laser driver. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> The input to our box is DC, from an external power supply. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> I do want a circuit that's foolproof, that always discharges >>>>>>>>>>>>>>> the caps >>>>>>>>>>>>>>> but doen't often go up in flames. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> A resistor makes an exponential decay which could be a very >>>>>>>>>>>>>>> long time >>>>>>>>>>>>>>> to get down to safe levels. >>>>>>>>>>>>>> >>>>>>>>>>>>>> But a resistor plus an inductor could give a critically damped >>>>>>>>>>>>>> decay, >>>>>>>>>>>>>> which would be quite a bit faster. I don't know enough about >>>>>>>>>>>>>> the circuit >>>>>>>>>>>>>> to be prepared to try to work out how much inductance you'd >>>>>>>>>>>>>> need, and >>>>>>>>>>>>>> you clearly can't be bothered. >>>>>>>>>>>>> >>>>>>>>>>>>> Won't be bothered. >>>>>>>>>>>>> >>>>>>>>>>>>>> >>>>>>>>>>>>>>> I thought the group might like a circuit design problem once >>>>>>>>>>>>>>> in a >>>>>>>>>>>>>>> while, a break from politics. >>>>>>>>>>>>>> >>>>>>>>>>>>>> But you don't do circuit design, and this sort of question >>>>>>>>>>>>>> makes it >>>>>>>>>>>>>> obvious why you don't. >>>>>>>>>>>>> >>>>>>>>>>>>> The inductor suggestion is hilarious. Thanks. >>>>>>>>>>>> >>>>>>>>>>>> It's elementary circuit theory, which you should have been >>>>>>>>>>>> taught and I >>>>>>>>>>>> had to read about. >>>>>>>>>>>> >>>>>>>>>>>> If you discharge a capacitor through a resistor, the voltage decays >>>>>>>>>>>> exponentially. If you put an inductor in series with the >>>>>>>>>>>> resistor the >>>>>>>>>>>> voltage decay is a more complicated function of time. If you >>>>>>>>>>>> chose the >>>>>>>>>>>> resistance and the inductance to create a critically damped >>>>>>>>>>>> circuit, the >>>>>>>>>>>> voltage across the capacitor will eventually decay more rapidly >>>>>>>>>>>> than >>>>>>>>>>>> you'd see with just the resistor. >>>>>>>>>>>> >>>>>>>>>>>> Try reading about Laplace transforms. That's a pretty hilarious >>>>>>>>>>>> suggestion to direct at you, but you are the butt of the joke. >>>>>>>>>>> >>>>>>>>>>> Oh, RLC circuits are no mystery. >>>>>>>>>>> >>>>>>>>>>> What's funny about the suggestion is the size of the inductor it >>>>>>>>>>> would >>>>>>>>>>> need. >>>>>>>>>> >>>>>>>>>> Which you haven't worked out. I spent a few minutes last night >>>>>>>>>> trying to >>>>>>>>>> work out what I could buy off the shelf from element-14 (the >>>>>>>>>> Australian >>>>>>>>>> branch of Newark) but their web-site has turned cranky in recent >>>>>>>>>> months. >>>>>>>>>> >>>>>>>>>> The value of the inductance isn't fixed - that and the resistor >>>>>>>>>> can be >>>>>>>>>> be chosen to get a critically damped LCR, and I figured that I'd >>>>>>>>>> start >>>>>>>>>> playing with an inductor I could buy. >>>>>>>>>> >>>>>>>>>> You might end up with a non-progressively wound air-cored toroid. >>>>>>>>>> With a >>>>>>>>>> 0.2F capacitor the parallel capacitance of the inductor isn't >>>>>>>>>> going to >>>>>>>>>> be an issue, and the winding resistance could be your damping >>>>>>>>>> resistor. >>>>>>>>>> >>>>>>>>>> 4kJ is a fair bit of energy, but you can get copper quite hot >>>>>>>>>> before it >>>>>>>>>> explodes. It wouldn't stay hot for long. >>>>>>>>>> >>>>>>>>> >>>>>>>>> I haven’t calculated what ballpark inductance might be required but >>>>>>>>> is air >>>>>>>>> core even feasible for that? >>>>>>>> >>>>>>>> If it were about the size of a truck maybe. >>>>>>>> >>>>>>>> You can estimate the inductance in your head. To discharge 0.2F in, >>>>>>>> say 100 seconds, you need 500 ohms. That would of course be the tau of >>>>>>>> an exponential decay. Adding an inductor would crisp that up. >>>>>>>> >>>>>>>> R*C = 100 seconds so we want L/R to be in that ballpark. >>>>>> >>>>>> 100 seconds is a lot too long from a safety point of view >>>>>> >>>>>>>> So L is around 50,000 H. >>>>>> >>>>>> If you start at the wrong end. >>>>>> >>>>>>>> Check Digikey for that. >>>>>>> >>>>>>> Critical damping happens when the expression for the impedance of >>>>>>> the series RLC has two identical roots. This happens when L = R^2C/4, >>>>>>> near enough, so L should be 12.5 kH. >>>>>> >>>>>> You can vary both L and R. A much shorter time constant means a much >>>>>> smaller inductor >>>>>> >>>>>> I dug out my copy of Grover and thought about a 5H air-cored inductor. >>>>>> >>>>>> 5H - a 1 sec time constant - would be practicable - but big. You'd >>>>>> need a great deal of copper wire to make it work. >>>>>> >>>>>> It might be worth thinking about an iron-cored inductor. We are >>>>>> looking at a fairly slow event so the current induced in the iron >>>>>> would be just one more dissipation mode. >>>>>> >>>>>> 0.5H might work. The time constant of 0.32 sec means that your 4kJ >>>>>> looks like 13kW while it is dissipating, but it would be being >>>>>> dissipated in what could be a fairly substantial resistor which >>>>>> wouldn't warm up much and would have time to cool off. >>>>>> >>>>>>> With the initial voltage 200V, it will need to briefly store just >>>>>>> short of 600 J. That doesn't look like a practical solution. >>>>>> >>>>>> Why not? Air-cored coils can store a lot of energy. If you put a lot >>>>>> of current through the turns the mechanical forces eventually rip them >>>>>> apart, but that's a very different regime. >>>>>> >>>>> >>>>> Because an air-core 12.5 kH inductor is *big*. >>>> >>>> As I managed to work out, after an unfortunate slip of the mind. >>>> >>>> 12.5KH is much bigger inductance than you would want or need. 100sec to >>>> discharge a capacitor is much too long. >>>> >>>> 5H and and 1sec makes much more sense but the air-cored inductor would >>>> still be impractically large. >>>> >>>> A carbonyl iron core might work >>>> >>>> https://www.rf-microwave.com/resources/products_attachments/67aa26a4a6d8c.pdf >>>> >>>> would need 16000 turns of 0.5mm OD copper wire to get to 5H. That's >>>> about 34 layers of wire about 2600 metres long, and the series >>>> resistance would be 230R, which is too high. >>>> >>>> 2.5mm OD wire might work, but that's only 100 tuns per layer, and 160 >>>> layers would over-fill the winding space. >>>> >>>> A bigger core could accommodate more turns of thicker wire, but that >>>> supplier doesn't do one. >>>> >>>> An iron tape core would offer more nH per root turn. They are >>>> commercially available and in larger sizes >>>> >>>> https://www.transmart.net/current-transformer-cores.html >>>> >>>> but the web-site isn't all that transparent, and clearly aimed at >>>> sophisticated users. >>> >>> You ignore simple rule of thumb: energy is more efficiently stored >>> in air. >> >> Efficiency is just the ratio of your solution to an ideal solution. >> >> You haven't indicated what you are comparing. >> >> Energy is more simply stored in an iron cored inductor because can get a >> higher inductance in a given volume - the iron eventually saturates >> which complicates life, and the iron would act as a shorted turn if you >> gave it half a chance. > > Approximate formula for maximal energy stored in inductor with a gap is: > > E = S*B_max^2*(l_i/mu + l_g)/(2*\mu_0) > > where E is the energy, B_max is maximal possible induction in the core, > S is surface area of the perpendicular cut through the core, l_i is > average length of magnetic path in the core, l_g is effective path > trough the gap, \mu is relative magnetic permeability of the core, > \mu_0 is magnetic permeability of the vacuum. > > The formula above assumes that you can pass whatever current is > needed through the winding and the only limit to current is due to > core saturation. As you can see better magnetic permeability > _decreases_ maximal possible energy, simply core will saturate > at lower current and gap significantly increases possible energy > storage. > > For comparison, formula for inductance is: > > L = N^2*S*\mu_0/(l_i/\mu + l_g) > > where N is number of turns and the other are as above. So design > for high energy will by neccessity have lower inductance. Winding > resistance is proportional to N^2, so if you need higher ratio > of inductance to resistance you need to go for bigger inductor > or lower stored energy. We all know about putting an air-gap in the magnetic path to increase the energy stored at the expense of the inductance you can get out of a given core. >>> So to get energy storage needed for critical >>> damping you need inductor as big or bigger than air cored >>> inductor. That depends on the energy you are trying to store.If you can store enough energy without saturating the core, the inductor can be a lot smaller than an air-cored inductor >> That doesn't follow. > > The formula above shows this clearly: removing core allows > bigger B and increases l_g term. Of course, once gap it > too big approximation is rather poor, but trend is clear. If you need to saturate the core, and it is beginning to looks as if John Larkin would have to. >>> You need a core because otherwise winding resistance >>> is likely to be too big for critical damping. >> >> We can all dream of superconducting wire, but all the versions I know of >> stop being super-conducting at a high enough magnetic field. I once got >> to clamber around the Nijmegen University's super-conducting magnet so I >> know that that can be a pretty high field. > > Yes. And we dream of superconducting wire which needs no refrigeration. That depends on the application. There are jobs that can pay for the refrigeration. Research magnets are the original examples, but there's going to be a magnetic resonance imaging system in a hospital near you. I've got one just down the street. High temperature super-conductors might work with just liquid nitrogen, which is cheap enough, but nobody wants to keep a rack of electronics submerged in liquid nitrogen. >>> It seems that inductor with EI core with the following dimensions >>> could satisfy the needs: >>> >>> Surface of the central column: 200 cm^2. >>> Side of cental column: 14.14 cm. >>> Height of cental column: 21.21 cm. >>> Width of winding window: 7.07 cm. >>> Total height of core: 35.35 cm >>> Total width of core: 42.42 cm >>> Total volume of core: 16962.87 cm^3 >>> Weight of the core: 129426.74 g >>> Air gap: 1cm >> >> You haven't specified the core material. My guess is that you would have >> to glom it together from rectangular lumps of ferrite. With that much >> air-gap, the exact material wouldn't matter much. > > I assumed iron. What matter is maximal allowed induction. Actually > AFAICS going slightly into saturation does not hurt, so I assumed > operation slightly above normal limits. But you didn't spell out that crucial detail. >> https://product.tdk.com/ >> >> lists a bunch. >> >>> To get L = 5H needs 1727 turns. I get 1.43 Ohm as winding resistance. >>> >>> So I guess that if one really needed such an inductor it would >>> be practical. But it is bulky. I am not sure if it is bigger >>> than the capacitor bank, but I expect it to be heavier. >> >> I'd be more interested in a toroidial core wound out of iron ribbon. >> >> https://megatron.ch/en/produkt-kategorie/ringbandkerne-und-schnittbandkerne/ >> >> Even with a high permeability (layered) iron core you'd still need quite >> a few turns to get a Henry or so of inductance. > > As I explained, main trouble is core saturation. The approximate > formula applies to toroids too. You didn't explain that at all in your original post, and you certainly didn't specify the saturation field you had in mind. >> The data sheets aren't exactly helpful. >> >> https://megatron.ch/infocenter/AMCC_100_Datenblatt.pdf -- Bill Sloman, Sydney
[toc] | [prev] | [next] | [standalone]
| From | John R Walliker <jrwalliker@gmail.com> |
|---|---|
| Date | 2026-09-13 19:40 +0100 |
| Message-ID | <1186qn2$s431$1@dont-email.me> |
| In reply to | #747671 |
On 13/09/2026 17:05, Bill Sloman wrote: > On 13/09/2026 11:36 pm, Waldek Hebisch wrote: >> Bill Sloman <bill.sloman@ieee.org> wrote: >>> On 13/09/2026 10:27 am, Waldek Hebisch wrote: >>>> Bill Sloman <bill.sloman@ieee.org> wrote: >>>>> >>>>> >>>>> On 10/09/2026 7:10 am, Jeroen Belleman wrote: >>>>>> On 9/9/26 17:32, Bill Sloman wrote: >>>>>>> On 9/09/2026 10:25 pm, Jeroen Belleman wrote: >>>>>>>> On 9/9/26 12:44, john larkin wrote: >>>>>>>>> On Wed, 9 Sep 2026 09:51:57 -0000 (UTC), piglet >>>>>>>>> <erichpwagner@hotmail.com> wrote: >>>>>>>>> >>>>>>>>>> Bill Sloman <bill.sloman@ieee.org> wrote: >>>>>>>>>>> On 9/09/2026 5:56 am, john larkin wrote: >>>>>>>>>>>> On Wed, 9 Sep 2026 03:09:41 +1000, Bill Sloman >>>>>>>>>>>> <bill.sloman@ieee.org> >>>>>>>>>>>> wrote: >>>>>>>>>>>> >>>>>>>>>>>>> On 9/09/2026 1:00 am, john larkin wrote: >>>>>>>>>>>>>> On Tue, 8 Sep 2026 17:35:24 +1000, Bill Sloman >>>>>>>>>>>>>> <bill.sloman@ieee.org> >>>>>>>>>>>>>> wrote: >>>>>>>>>>>>>> >>>>>>>>>>>>>>> On 8/09/2026 4:52 am, john larkin wrote: >>>>>>>>>>>>>>>> On Mon, 7 Sep 2026 19:33:35 +0100, chrisq >>>>>>>>>>>>>>>> <syseng@gfsys.co.uk> wrote: >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> On 9/7/26 16:18, john larkin wrote: >>>>>>>>>>>>>>>>>> Suppose we have a box with some big caps inside, for >>>>>>>>>>>>>>>>>> example 0.2 >>>>>>>>>>>>>>>>>> farads that run at about 200 volts. When AC power is off, >>>>>>>>>>>>>>>>>> we want to >>>>>>>>>>>>>>>>>> discharge them for several reasons. >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> Putting, say, a 1K resistor across them dissipates 40 >>>>>>>>>>>>>>>>>> watts >>>>>>>>>>>>>>>>>> and has a >>>>>>>>>>>>>>>>>> 200 second time constant. It will take many tau before >>>>>>>>>>>>>>>>>> the >>>>>>>>>>>>>>>>>> voltage >>>>>>>>>>>>>>>>>> gets low enough for people to poke around inside. >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> The ideal discharger would be a constant-current or even >>>>>>>>>>>>>>>>>> better a >>>>>>>>>>>>>>>>>> constant-power load, all the way down to zero volts. It >>>>>>>>>>>>>>>>>> would be dumb, >>>>>>>>>>>>>>>>>> not switched by some decision circuit or anything fancy >>>>>>>>>>>>>>>>>> like that. >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> And of course we need several LEDs as warnings that the >>>>>>>>>>>>>>>>>> thing is hot. >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> What sort of design needs 0.2 Farad cap, at 200 >>>>>>>>>>>>>>>>> volts ?. If >>>>>>>>>>>>>>>>> you are >>>>>>>>>>>>>>>>> working at that level, put in a cheap relay and a rated >>>>>>>>>>>>>>>>> heatsink >>>>>>>>>>>>>>>>> wirewound resistor to dump the energy, when the power >>>>>>>>>>>>>>>>> goes off. >>>>>>>>>>>>>>>>> Cheap, and lossless as well. Motor drive inverters >>>>>>>>>>>>>>>>> often have >>>>>>>>>>>>>>>>> big resistors to brake the motor. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> John Larkin >>>>>>>>>>>>>>>>>> Highland Tech Glen Canyon Design Center >>>>>>>>>>>>>>>>>> Lunatic Fringe Electronics >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> It's a 1500 amp laser driver. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> The input to our box is DC, from an external power supply. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> I do want a circuit that's foolproof, that always >>>>>>>>>>>>>>>> discharges >>>>>>>>>>>>>>>> the caps >>>>>>>>>>>>>>>> but doen't often go up in flames. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> A resistor makes an exponential decay which could be a very >>>>>>>>>>>>>>>> long time >>>>>>>>>>>>>>>> to get down to safe levels. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> But a resistor plus an inductor could give a critically >>>>>>>>>>>>>>> damped >>>>>>>>>>>>>>> decay, >>>>>>>>>>>>>>> which would be quite a bit faster. I don't know enough about >>>>>>>>>>>>>>> the circuit >>>>>>>>>>>>>>> to be prepared to try to work out how much inductance you'd >>>>>>>>>>>>>>> need, and >>>>>>>>>>>>>>> you clearly can't be bothered. >>>>>>>>>>>>>> >>>>>>>>>>>>>> Won't be bothered. >>>>>>>>>>>>>> >>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> I thought the group might like a circuit design problem >>>>>>>>>>>>>>>> once >>>>>>>>>>>>>>>> in a >>>>>>>>>>>>>>>> while, a break from politics. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> But you don't do circuit design, and this sort of question >>>>>>>>>>>>>>> makes it >>>>>>>>>>>>>>> obvious why you don't. >>>>>>>>>>>>>> >>>>>>>>>>>>>> The inductor suggestion is hilarious. Thanks. >>>>>>>>>>>>> >>>>>>>>>>>>> It's elementary circuit theory, which you should have been >>>>>>>>>>>>> taught and I >>>>>>>>>>>>> had to read about. >>>>>>>>>>>>> >>>>>>>>>>>>> If you discharge a capacitor through a resistor, the >>>>>>>>>>>>> voltage decays >>>>>>>>>>>>> exponentially. If you put an inductor in series with the >>>>>>>>>>>>> resistor the >>>>>>>>>>>>> voltage decay is a more complicated function of time. If you >>>>>>>>>>>>> chose the >>>>>>>>>>>>> resistance and the inductance to create a critically damped >>>>>>>>>>>>> circuit, the >>>>>>>>>>>>> voltage across the capacitor will eventually decay more >>>>>>>>>>>>> rapidly >>>>>>>>>>>>> than >>>>>>>>>>>>> you'd see with just the resistor. >>>>>>>>>>>>> >>>>>>>>>>>>> Try reading about Laplace transforms. That's a pretty >>>>>>>>>>>>> hilarious >>>>>>>>>>>>> suggestion to direct at you, but you are the butt of the joke. >>>>>>>>>>>> >>>>>>>>>>>> Oh, RLC circuits are no mystery. >>>>>>>>>>>> >>>>>>>>>>>> What's funny about the suggestion is the size of the >>>>>>>>>>>> inductor it >>>>>>>>>>>> would >>>>>>>>>>>> need. >>>>>>>>>>> >>>>>>>>>>> Which you haven't worked out. I spent a few minutes last night >>>>>>>>>>> trying to >>>>>>>>>>> work out what I could buy off the shelf from element-14 (the >>>>>>>>>>> Australian >>>>>>>>>>> branch of Newark) but their web-site has turned cranky in recent >>>>>>>>>>> months. >>>>>>>>>>> >>>>>>>>>>> The value of the inductance isn't fixed - that and the resistor >>>>>>>>>>> can be >>>>>>>>>>> be chosen to get a critically damped LCR, and I figured that I'd >>>>>>>>>>> start >>>>>>>>>>> playing with an inductor I could buy. >>>>>>>>>>> >>>>>>>>>>> You might end up with a non-progressively wound air-cored >>>>>>>>>>> toroid. >>>>>>>>>>> With a >>>>>>>>>>> 0.2F capacitor the parallel capacitance of the inductor isn't >>>>>>>>>>> going to >>>>>>>>>>> be an issue, and the winding resistance could be your damping >>>>>>>>>>> resistor. >>>>>>>>>>> >>>>>>>>>>> 4kJ is a fair bit of energy, but you can get copper quite hot >>>>>>>>>>> before it >>>>>>>>>>> explodes. It wouldn't stay hot for long. >>>>>>>>>>> >>>>>>>>>> >>>>>>>>>> I haven’t calculated what ballpark inductance might be >>>>>>>>>> required but >>>>>>>>>> is air >>>>>>>>>> core even feasible for that? >>>>>>>>> >>>>>>>>> If it were about the size of a truck maybe. >>>>>>>>> >>>>>>>>> You can estimate the inductance in your head. To discharge 0.2F >>>>>>>>> in, >>>>>>>>> say 100 seconds, you need 500 ohms. That would of course be the >>>>>>>>> tau of >>>>>>>>> an exponential decay. Adding an inductor would crisp that up. >>>>>>>>> >>>>>>>>> R*C = 100 seconds so we want L/R to be in that ballpark. >>>>>>> >>>>>>> 100 seconds is a lot too long from a safety point of view >>>>>>> >>>>>>>>> So L is around 50,000 H. >>>>>>> >>>>>>> If you start at the wrong end. >>>>>>> >>>>>>>>> Check Digikey for that. >>>>>>>> >>>>>>>> Critical damping happens when the expression for the impedance of >>>>>>>> the series RLC has two identical roots. This happens when L = >>>>>>>> R^2C/4, >>>>>>>> near enough, so L should be 12.5 kH. >>>>>>> >>>>>>> You can vary both L and R. A much shorter time constant means a much >>>>>>> smaller inductor >>>>>>> >>>>>>> I dug out my copy of Grover and thought about a 5H air-cored >>>>>>> inductor. >>>>>>> >>>>>>> 5H - a 1 sec time constant - would be practicable - but big. You'd >>>>>>> need a great deal of copper wire to make it work. >>>>>>> >>>>>>> It might be worth thinking about an iron-cored inductor. We are >>>>>>> looking at a fairly slow event so the current induced in the iron >>>>>>> would be just one more dissipation mode. >>>>>>> >>>>>>> 0.5H might work. The time constant of 0.32 sec means that your 4kJ >>>>>>> looks like 13kW while it is dissipating, but it would be being >>>>>>> dissipated in what could be a fairly substantial resistor which >>>>>>> wouldn't warm up much and would have time to cool off. >>>>>>> >>>>>>>> With the initial voltage 200V, it will need to briefly store just >>>>>>>> short of 600 J. That doesn't look like a practical solution. >>>>>>> >>>>>>> Why not? Air-cored coils can store a lot of energy. If you put a lot >>>>>>> of current through the turns the mechanical forces eventually rip >>>>>>> them >>>>>>> apart, but that's a very different regime. >>>>>>> >>>>>> >>>>>> Because an air-core 12.5 kH inductor is *big*. >>>>> >>>>> As I managed to work out, after an unfortunate slip of the mind. >>>>> >>>>> 12.5KH is much bigger inductance than you would want or need. >>>>> 100sec to >>>>> discharge a capacitor is much too long. >>>>> >>>>> 5H and and 1sec makes much more sense but the air-cored inductor would >>>>> still be impractically large. >>>>> >>>>> A carbonyl iron core might work >>>>> >>>>> https://www.rf-microwave.com/resources/ >>>>> products_attachments/67aa26a4a6d8c.pdf >>>>> >>>>> would need 16000 turns of 0.5mm OD copper wire to get to 5H. That's >>>>> about 34 layers of wire about 2600 metres long, and the series >>>>> resistance would be 230R, which is too high. >>>>> >>>>> 2.5mm OD wire might work, but that's only 100 tuns per layer, and 160 >>>>> layers would over-fill the winding space. >>>>> >>>>> A bigger core could accommodate more turns of thicker wire, but that >>>>> supplier doesn't do one. >>>>> >>>>> An iron tape core would offer more nH per root turn. They are >>>>> commercially available and in larger sizes >>>>> >>>>> https://www.transmart.net/current-transformer-cores.html >>>>> >>>>> but the web-site isn't all that transparent, and clearly aimed at >>>>> sophisticated users. >>>> >>>> You ignore simple rule of thumb: energy is more efficiently stored >>>> in air. >>> >>> Efficiency is just the ratio of your solution to an ideal solution. >>> >>> You haven't indicated what you are comparing. >>> >>> Energy is more simply stored in an iron cored inductor because can get a >>> higher inductance in a given volume - the iron eventually saturates >>> which complicates life, and the iron would act as a shorted turn if you >>> gave it half a chance. >> >> Approximate formula for maximal energy stored in inductor with a gap is: >> >> E = S*B_max^2*(l_i/mu + l_g)/(2*\mu_0) >> >> where E is the energy, B_max is maximal possible induction in the core, >> S is surface area of the perpendicular cut through the core, l_i is >> average length of magnetic path in the core, l_g is effective path >> trough the gap, \mu is relative magnetic permeability of the core, >> \mu_0 is magnetic permeability of the vacuum. >> >> The formula above assumes that you can pass whatever current is >> needed through the winding and the only limit to current is due to >> core saturation. As you can see better magnetic permeability >> _decreases_ maximal possible energy, simply core will saturate >> at lower current and gap significantly increases possible energy >> storage. >> >> For comparison, formula for inductance is: >> >> L = N^2*S*\mu_0/(l_i/\mu + l_g) >> >> where N is number of turns and the other are as above. So design >> for high energy will by neccessity have lower inductance. Winding >> resistance is proportional to N^2, so if you need higher ratio >> of inductance to resistance you need to go for bigger inductor >> or lower stored energy. > > We all know about putting an air-gap in the magnetic path to increase > the energy stored at the expense of the inductance you can get out of a > given core. > >>>> So to get energy storage needed for critical >>>> damping you need inductor as big or bigger than air cored >>>> inductor. > > That depends on the energy you are trying to store.If you can store > enough energy without saturating the core, the inductor can be a lot > smaller than an air-cored inductor > >>> That doesn't follow. >> >> The formula above shows this clearly: removing core allows >> bigger B and increases l_g term. Of course, once gap it >> too big approximation is rather poor, but trend is clear. > > If you need to saturate the core, and it is beginning to looks as if > John Larkin would have to. > >>>> You need a core because otherwise winding resistance >>>> is likely to be too big for critical damping. >>> >>> We can all dream of superconducting wire, but all the versions I know of >>> stop being super-conducting at a high enough magnetic field. I once got >>> to clamber around the Nijmegen University's super-conducting magnet so I >>> know that that can be a pretty high field. >> >> Yes. And we dream of superconducting wire which needs no refrigeration. > > That depends on the application. There are jobs that can pay for the > refrigeration. Research magnets are the original examples, but there's > going to be a magnetic resonance imaging system in a hospital near you. > I've got one just down the street. > > High temperature super-conductors might work with just liquid nitrogen, > which is cheap enough, but nobody wants to keep a rack of electronics > submerged in liquid nitrogen. > >>>> It seems that inductor with EI core with the following dimensions >>>> could satisfy the needs: >>>> >>>> Surface of the central column: 200 cm^2. >>>> Side of cental column: 14.14 cm. >>>> Height of cental column: 21.21 cm. >>>> Width of winding window: 7.07 cm. >>>> Total height of core: 35.35 cm >>>> Total width of core: 42.42 cm >>>> Total volume of core: 16962.87 cm^3 >>>> Weight of the core: 129426.74 g >>>> Air gap: 1cm >>> >>> You haven't specified the core material. My guess is that you would have >>> to glom it together from rectangular lumps of ferrite. With that much >>> air-gap, the exact material wouldn't matter much. >> >> I assumed iron. What matter is maximal allowed induction. Actually >> AFAICS going slightly into saturation does not hurt, so I assumed >> operation slightly above normal limits. > > But you didn't spell out that crucial detail. > >>> https://product.tdk.com/ >>> >>> lists a bunch. >>> >>>> To get L = 5H needs 1727 turns. I get 1.43 Ohm as winding resistance. >>>> >>>> So I guess that if one really needed such an inductor it would >>>> be practical. But it is bulky. I am not sure if it is bigger >>>> than the capacitor bank, but I expect it to be heavier. >>> >>> I'd be more interested in a toroidial core wound out of iron ribbon. >>> >>> https://megatron.ch/en/produkt-kategorie/ringbandkerne-und- >>> schnittbandkerne/ >>> >>> Even with a high permeability (layered) iron core you'd still need quite >>> a few turns to get a Henry or so of inductance. >> >> As I explained, main trouble is core saturation. The approximate >> formula applies to toroids too. > > You didn't explain that at all in your original post, and you certainly > didn't specify the saturation field you had in mind. > >>> The data sheets aren't exactly helpful. >>> >>> https://megatron.ch/infocenter/AMCC_100_Datenblatt.pdf > This seems to be ridiculously over-complicated. It probably takes a couple of minutes to undo all the screws holding down the lid of the box. Once the voltage has fallen below 60V it is not considered to be hazardous according to most safety standards. Why do anything complicated when a very simple solution will get the voltage to a reasonable value in the time it takes to get the lid off? Using an inductor to speed up the voltage decay seems totally unnecessary. John
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| From | john larkin <jl@glen--canyon.com> |
|---|---|
| Date | 2026-09-13 12:08 -0700 |
| Message-ID | <1vsdallvr24as5l8r7aetbbejda54i254a@4ax.com> |
| In reply to | #747681 |
On Sun, 13 Sep 2026 19:40:33 +0100, John R Walliker <jrwalliker@gmail.com> wrote: >On 13/09/2026 17:05, Bill Sloman wrote: >> On 13/09/2026 11:36 pm, Waldek Hebisch wrote: >>> Bill Sloman <bill.sloman@ieee.org> wrote: >>>> On 13/09/2026 10:27 am, Waldek Hebisch wrote: >>>>> Bill Sloman <bill.sloman@ieee.org> wrote: >>>>>> >>>>>> >>>>>> On 10/09/2026 7:10 am, Jeroen Belleman wrote: >>>>>>> On 9/9/26 17:32, Bill Sloman wrote: >>>>>>>> On 9/09/2026 10:25 pm, Jeroen Belleman wrote: >>>>>>>>> On 9/9/26 12:44, john larkin wrote: >>>>>>>>>> On Wed, 9 Sep 2026 09:51:57 -0000 (UTC), piglet >>>>>>>>>> <erichpwagner@hotmail.com> wrote: >>>>>>>>>> >>>>>>>>>>> Bill Sloman <bill.sloman@ieee.org> wrote: >>>>>>>>>>>> On 9/09/2026 5:56 am, john larkin wrote: >>>>>>>>>>>>> On Wed, 9 Sep 2026 03:09:41 +1000, Bill Sloman >>>>>>>>>>>>> <bill.sloman@ieee.org> >>>>>>>>>>>>> wrote: >>>>>>>>>>>>> >>>>>>>>>>>>>> On 9/09/2026 1:00 am, john larkin wrote: >>>>>>>>>>>>>>> On Tue, 8 Sep 2026 17:35:24 +1000, Bill Sloman >>>>>>>>>>>>>>> <bill.sloman@ieee.org> >>>>>>>>>>>>>>> wrote: >>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> On 8/09/2026 4:52 am, john larkin wrote: >>>>>>>>>>>>>>>>> On Mon, 7 Sep 2026 19:33:35 +0100, chrisq >>>>>>>>>>>>>>>>> <syseng@gfsys.co.uk> wrote: >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> On 9/7/26 16:18, john larkin wrote: >>>>>>>>>>>>>>>>>>> Suppose we have a box with some big caps inside, for >>>>>>>>>>>>>>>>>>> example 0.2 >>>>>>>>>>>>>>>>>>> farads that run at about 200 volts. When AC power is off, >>>>>>>>>>>>>>>>>>> we want to >>>>>>>>>>>>>>>>>>> discharge them for several reasons. >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> Putting, say, a 1K resistor across them dissipates 40 >>>>>>>>>>>>>>>>>>> watts >>>>>>>>>>>>>>>>>>> and has a >>>>>>>>>>>>>>>>>>> 200 second time constant. It will take many tau before >>>>>>>>>>>>>>>>>>> the >>>>>>>>>>>>>>>>>>> voltage >>>>>>>>>>>>>>>>>>> gets low enough for people to poke around inside. >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> The ideal discharger would be a constant-current or even >>>>>>>>>>>>>>>>>>> better a >>>>>>>>>>>>>>>>>>> constant-power load, all the way down to zero volts. It >>>>>>>>>>>>>>>>>>> would be dumb, >>>>>>>>>>>>>>>>>>> not switched by some decision circuit or anything fancy >>>>>>>>>>>>>>>>>>> like that. >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> And of course we need several LEDs as warnings that the >>>>>>>>>>>>>>>>>>> thing is hot. >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> What sort of design needs 0.2 Farad cap, at 200 >>>>>>>>>>>>>>>>>> volts ?. If >>>>>>>>>>>>>>>>>> you are >>>>>>>>>>>>>>>>>> working at that level, put in a cheap relay and a rated >>>>>>>>>>>>>>>>>> heatsink >>>>>>>>>>>>>>>>>> wirewound resistor to dump the energy, when the power >>>>>>>>>>>>>>>>>> goes off. >>>>>>>>>>>>>>>>>> Cheap, and lossless as well. Motor drive inverters >>>>>>>>>>>>>>>>>> often have >>>>>>>>>>>>>>>>>> big resistors to brake the motor. >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> John Larkin >>>>>>>>>>>>>>>>>>> Highland Tech Glen Canyon Design Center >>>>>>>>>>>>>>>>>>> Lunatic Fringe Electronics >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> It's a 1500 amp laser driver. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> The input to our box is DC, from an external power supply. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> I do want a circuit that's foolproof, that always >>>>>>>>>>>>>>>>> discharges >>>>>>>>>>>>>>>>> the caps >>>>>>>>>>>>>>>>> but doen't often go up in flames. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> A resistor makes an exponential decay which could be a very >>>>>>>>>>>>>>>>> long time >>>>>>>>>>>>>>>>> to get down to safe levels. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> But a resistor plus an inductor could give a critically >>>>>>>>>>>>>>>> damped >>>>>>>>>>>>>>>> decay, >>>>>>>>>>>>>>>> which would be quite a bit faster. I don't know enough about >>>>>>>>>>>>>>>> the circuit >>>>>>>>>>>>>>>> to be prepared to try to work out how much inductance you'd >>>>>>>>>>>>>>>> need, and >>>>>>>>>>>>>>>> you clearly can't be bothered. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Won't be bothered. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> I thought the group might like a circuit design problem >>>>>>>>>>>>>>>>> once >>>>>>>>>>>>>>>>> in a >>>>>>>>>>>>>>>>> while, a break from politics. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> But you don't do circuit design, and this sort of question >>>>>>>>>>>>>>>> makes it >>>>>>>>>>>>>>>> obvious why you don't. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> The inductor suggestion is hilarious. Thanks. >>>>>>>>>>>>>> >>>>>>>>>>>>>> It's elementary circuit theory, which you should have been >>>>>>>>>>>>>> taught and I >>>>>>>>>>>>>> had to read about. >>>>>>>>>>>>>> >>>>>>>>>>>>>> If you discharge a capacitor through a resistor, the >>>>>>>>>>>>>> voltage decays >>>>>>>>>>>>>> exponentially. If you put an inductor in series with the >>>>>>>>>>>>>> resistor the >>>>>>>>>>>>>> voltage decay is a more complicated function of time. If you >>>>>>>>>>>>>> chose the >>>>>>>>>>>>>> resistance and the inductance to create a critically damped >>>>>>>>>>>>>> circuit, the >>>>>>>>>>>>>> voltage across the capacitor will eventually decay more >>>>>>>>>>>>>> rapidly >>>>>>>>>>>>>> than >>>>>>>>>>>>>> you'd see with just the resistor. >>>>>>>>>>>>>> >>>>>>>>>>>>>> Try reading about Laplace transforms. That's a pretty >>>>>>>>>>>>>> hilarious >>>>>>>>>>>>>> suggestion to direct at you, but you are the butt of the joke. >>>>>>>>>>>>> >>>>>>>>>>>>> Oh, RLC circuits are no mystery. >>>>>>>>>>>>> >>>>>>>>>>>>> What's funny about the suggestion is the size of the >>>>>>>>>>>>> inductor it >>>>>>>>>>>>> would >>>>>>>>>>>>> need. >>>>>>>>>>>> >>>>>>>>>>>> Which you haven't worked out. I spent a few minutes last night >>>>>>>>>>>> trying to >>>>>>>>>>>> work out what I could buy off the shelf from element-14 (the >>>>>>>>>>>> Australian >>>>>>>>>>>> branch of Newark) but their web-site has turned cranky in recent >>>>>>>>>>>> months. >>>>>>>>>>>> >>>>>>>>>>>> The value of the inductance isn't fixed - that and the resistor >>>>>>>>>>>> can be >>>>>>>>>>>> be chosen to get a critically damped LCR, and I figured that I'd >>>>>>>>>>>> start >>>>>>>>>>>> playing with an inductor I could buy. >>>>>>>>>>>> >>>>>>>>>>>> You might end up with a non-progressively wound air-cored >>>>>>>>>>>> toroid. >>>>>>>>>>>> With a >>>>>>>>>>>> 0.2F capacitor the parallel capacitance of the inductor isn't >>>>>>>>>>>> going to >>>>>>>>>>>> be an issue, and the winding resistance could be your damping >>>>>>>>>>>> resistor. >>>>>>>>>>>> >>>>>>>>>>>> 4kJ is a fair bit of energy, but you can get copper quite hot >>>>>>>>>>>> before it >>>>>>>>>>>> explodes. It wouldn't stay hot for long. >>>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> I haven’t calculated what ballpark inductance might be >>>>>>>>>>> required but >>>>>>>>>>> is air >>>>>>>>>>> core even feasible for that? >>>>>>>>>> >>>>>>>>>> If it were about the size of a truck maybe. >>>>>>>>>> >>>>>>>>>> You can estimate the inductance in your head. To discharge 0.2F >>>>>>>>>> in, >>>>>>>>>> say 100 seconds, you need 500 ohms. That would of course be the >>>>>>>>>> tau of >>>>>>>>>> an exponential decay. Adding an inductor would crisp that up. >>>>>>>>>> >>>>>>>>>> R*C = 100 seconds so we want L/R to be in that ballpark. >>>>>>>> >>>>>>>> 100 seconds is a lot too long from a safety point of view >>>>>>>> >>>>>>>>>> So L is around 50,000 H. >>>>>>>> >>>>>>>> If you start at the wrong end. >>>>>>>> >>>>>>>>>> Check Digikey for that. >>>>>>>>> >>>>>>>>> Critical damping happens when the expression for the impedance of >>>>>>>>> the series RLC has two identical roots. This happens when L = >>>>>>>>> R^2C/4, >>>>>>>>> near enough, so L should be 12.5 kH. >>>>>>>> >>>>>>>> You can vary both L and R. A much shorter time constant means a much >>>>>>>> smaller inductor >>>>>>>> >>>>>>>> I dug out my copy of Grover and thought about a 5H air-cored >>>>>>>> inductor. >>>>>>>> >>>>>>>> 5H - a 1 sec time constant - would be practicable - but big. You'd >>>>>>>> need a great deal of copper wire to make it work. >>>>>>>> >>>>>>>> It might be worth thinking about an iron-cored inductor. We are >>>>>>>> looking at a fairly slow event so the current induced in the iron >>>>>>>> would be just one more dissipation mode. >>>>>>>> >>>>>>>> 0.5H might work. The time constant of 0.32 sec means that your 4kJ >>>>>>>> looks like 13kW while it is dissipating, but it would be being >>>>>>>> dissipated in what could be a fairly substantial resistor which >>>>>>>> wouldn't warm up much and would have time to cool off. >>>>>>>> >>>>>>>>> With the initial voltage 200V, it will need to briefly store just >>>>>>>>> short of 600 J. That doesn't look like a practical solution. >>>>>>>> >>>>>>>> Why not? Air-cored coils can store a lot of energy. If you put a lot >>>>>>>> of current through the turns the mechanical forces eventually rip >>>>>>>> them >>>>>>>> apart, but that's a very different regime. >>>>>>>> >>>>>>> >>>>>>> Because an air-core 12.5 kH inductor is *big*. >>>>>> >>>>>> As I managed to work out, after an unfortunate slip of the mind. >>>>>> >>>>>> 12.5KH is much bigger inductance than you would want or need. >>>>>> 100sec to >>>>>> discharge a capacitor is much too long. >>>>>> >>>>>> 5H and and 1sec makes much more sense but the air-cored inductor would >>>>>> still be impractically large. >>>>>> >>>>>> A carbonyl iron core might work >>>>>> >>>>>> https://www.rf-microwave.com/resources/ >>>>>> products_attachments/67aa26a4a6d8c.pdf >>>>>> >>>>>> would need 16000 turns of 0.5mm OD copper wire to get to 5H. That's >>>>>> about 34 layers of wire about 2600 metres long, and the series >>>>>> resistance would be 230R, which is too high. >>>>>> >>>>>> 2.5mm OD wire might work, but that's only 100 tuns per layer, and 160 >>>>>> layers would over-fill the winding space. >>>>>> >>>>>> A bigger core could accommodate more turns of thicker wire, but that >>>>>> supplier doesn't do one. >>>>>> >>>>>> An iron tape core would offer more nH per root turn. They are >>>>>> commercially available and in larger sizes >>>>>> >>>>>> https://www.transmart.net/current-transformer-cores.html >>>>>> >>>>>> but the web-site isn't all that transparent, and clearly aimed at >>>>>> sophisticated users. >>>>> >>>>> You ignore simple rule of thumb: energy is more efficiently stored >>>>> in air. >>>> >>>> Efficiency is just the ratio of your solution to an ideal solution. >>>> >>>> You haven't indicated what you are comparing. >>>> >>>> Energy is more simply stored in an iron cored inductor because can get a >>>> higher inductance in a given volume - the iron eventually saturates >>>> which complicates life, and the iron would act as a shorted turn if you >>>> gave it half a chance. >>> >>> Approximate formula for maximal energy stored in inductor with a gap is: >>> >>> E = S*B_max^2*(l_i/mu + l_g)/(2*\mu_0) >>> >>> where E is the energy, B_max is maximal possible induction in the core, >>> S is surface area of the perpendicular cut through the core, l_i is >>> average length of magnetic path in the core, l_g is effective path >>> trough the gap, \mu is relative magnetic permeability of the core, >>> \mu_0 is magnetic permeability of the vacuum. >>> >>> The formula above assumes that you can pass whatever current is >>> needed through the winding and the only limit to current is due to >>> core saturation. As you can see better magnetic permeability >>> _decreases_ maximal possible energy, simply core will saturate >>> at lower current and gap significantly increases possible energy >>> storage. >>> >>> For comparison, formula for inductance is: >>> >>> L = N^2*S*\mu_0/(l_i/\mu + l_g) >>> >>> where N is number of turns and the other are as above. So design >>> for high energy will by neccessity have lower inductance. Winding >>> resistance is proportional to N^2, so if you need higher ratio >>> of inductance to resistance you need to go for bigger inductor >>> or lower stored energy. >> >> We all know about putting an air-gap in the magnetic path to increase >> the energy stored at the expense of the inductance you can get out of a >> given core. >> >>>>> So to get energy storage needed for critical >>>>> damping you need inductor as big or bigger than air cored >>>>> inductor. >> >> That depends on the energy you are trying to store.If you can store >> enough energy without saturating the core, the inductor can be a lot >> smaller than an air-cored inductor >> >>>> That doesn't follow. >>> >>> The formula above shows this clearly: removing core allows >>> bigger B and increases l_g term. Of course, once gap it >>> too big approximation is rather poor, but trend is clear. >> >> If you need to saturate the core, and it is beginning to looks as if >> John Larkin would have to. >> >>>>> You need a core because otherwise winding resistance >>>>> is likely to be too big for critical damping. >>>> >>>> We can all dream of superconducting wire, but all the versions I know of >>>> stop being super-conducting at a high enough magnetic field. I once got >>>> to clamber around the Nijmegen University's super-conducting magnet so I >>>> know that that can be a pretty high field. >>> >>> Yes. And we dream of superconducting wire which needs no refrigeration. >> >> That depends on the application. There are jobs that can pay for the >> refrigeration. Research magnets are the original examples, but there's >> going to be a magnetic resonance imaging system in a hospital near you. >> I've got one just down the street. >> >> High temperature super-conductors might work with just liquid nitrogen, >> which is cheap enough, but nobody wants to keep a rack of electronics >> submerged in liquid nitrogen. >> >>>>> It seems that inductor with EI core with the following dimensions >>>>> could satisfy the needs: >>>>> >>>>> Surface of the central column: 200 cm^2. >>>>> Side of cental column: 14.14 cm. >>>>> Height of cental column: 21.21 cm. >>>>> Width of winding window: 7.07 cm. >>>>> Total height of core: 35.35 cm >>>>> Total width of core: 42.42 cm >>>>> Total volume of core: 16962.87 cm^3 >>>>> Weight of the core: 129426.74 g >>>>> Air gap: 1cm >>>> >>>> You haven't specified the core material. My guess is that you would have >>>> to glom it together from rectangular lumps of ferrite. With that much >>>> air-gap, the exact material wouldn't matter much. >>> >>> I assumed iron. What matter is maximal allowed induction. Actually >>> AFAICS going slightly into saturation does not hurt, so I assumed >>> operation slightly above normal limits. >> >> But you didn't spell out that crucial detail. >> >>>> https://product.tdk.com/ >>>> >>>> lists a bunch. >>>> >>>>> To get L = 5H needs 1727 turns. I get 1.43 Ohm as winding resistance. >>>>> >>>>> So I guess that if one really needed such an inductor it would >>>>> be practical. But it is bulky. I am not sure if it is bigger >>>>> than the capacitor bank, but I expect it to be heavier. >>>> >>>> I'd be more interested in a toroidial core wound out of iron ribbon. >>>> >>>> https://megatron.ch/en/produkt-kategorie/ringbandkerne-und- >>>> schnittbandkerne/ >>>> >>>> Even with a high permeability (layered) iron core you'd still need quite >>>> a few turns to get a Henry or so of inductance. >>> >>> As I explained, main trouble is core saturation. The approximate >>> formula applies to toroids too. >> >> You didn't explain that at all in your original post, and you certainly >> didn't specify the saturation field you had in mind. >> >>>> The data sheets aren't exactly helpful. >>>> >>>> https://megatron.ch/infocenter/AMCC_100_Datenblatt.pdf >> > >This seems to be ridiculously over-complicated. It probably takes >a couple of minutes to undo all the screws holding down the lid of the >box. Once the voltage has fallen below 60V it is not considered >to be hazardous according to most safety standards. >Why do anything complicated when a very simple solution will get the >voltage to a reasonable value in the time it takes to get the lid off? >Using an inductor to speed up the voltage decay seems totally >unnecessary. >John Yes, the inductor idea is silly. But even 60 volts in those caps, shorted, makes a gigantic bang. All I need is a simple, ultra-reliable circuit to discharge the caps to zero volts in under two minutes. And a lot of LEDs to show when it's not done. John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
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| From | Bill Sloman <bill.sloman@ieee.org> |
|---|---|
| Date | 2026-09-14 16:18 +1000 |
| Message-ID | <11883j7$18ct6$5@dont-email.me> |
| In reply to | #747686 |
On 14/09/2026 5:08 am, john larkin wrote: > On Sun, 13 Sep 2026 19:40:33 +0100, John R Walliker > <jrwalliker@gmail.com> wrote: > >> On 13/09/2026 17:05, Bill Sloman wrote: >>> On 13/09/2026 11:36 pm, Waldek Hebisch wrote: >>>> Bill Sloman <bill.sloman@ieee.org> wrote: >>>>> On 13/09/2026 10:27 am, Waldek Hebisch wrote: >>>>>> Bill Sloman <bill.sloman@ieee.org> wrote: >>>>>>> >>>>>>> >>>>>>> On 10/09/2026 7:10 am, Jeroen Belleman wrote: >>>>>>>> On 9/9/26 17:32, Bill Sloman wrote: >>>>>>>>> On 9/09/2026 10:25 pm, Jeroen Belleman wrote: >>>>>>>>>> On 9/9/26 12:44, john larkin wrote: >>>>>>>>>>> On Wed, 9 Sep 2026 09:51:57 -0000 (UTC), piglet >>>>>>>>>>> <erichpwagner@hotmail.com> wrote: >>>>>>>>>>> >>>>>>>>>>>> Bill Sloman <bill.sloman@ieee.org> wrote: >>>>>>>>>>>>> On 9/09/2026 5:56 am, john larkin wrote: >>>>>>>>>>>>>> On Wed, 9 Sep 2026 03:09:41 +1000, Bill Sloman >>>>>>>>>>>>>> <bill.sloman@ieee.org> >>>>>>>>>>>>>> wrote: >>>>>>>>>>>>>> >>>>>>>>>>>>>>> On 9/09/2026 1:00 am, john larkin wrote: >>>>>>>>>>>>>>>> On Tue, 8 Sep 2026 17:35:24 +1000, Bill Sloman >>>>>>>>>>>>>>>> <bill.sloman@ieee.org> >>>>>>>>>>>>>>>> wrote: >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> On 8/09/2026 4:52 am, john larkin wrote: >>>>>>>>>>>>>>>>>> On Mon, 7 Sep 2026 19:33:35 +0100, chrisq >>>>>>>>>>>>>>>>>> <syseng@gfsys.co.uk> wrote: >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> On 9/7/26 16:18, john larkin wrote: >>>>>>>>>>>>>>>>>>>> Suppose we have a box with some big caps inside, for >>>>>>>>>>>>>>>>>>>> example 0.2 >>>>>>>>>>>>>>>>>>>> farads that run at about 200 volts. When AC power is off, >>>>>>>>>>>>>>>>>>>> we want to >>>>>>>>>>>>>>>>>>>> discharge them for several reasons. >>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>> Putting, say, a 1K resistor across them dissipates 40 >>>>>>>>>>>>>>>>>>>> watts >>>>>>>>>>>>>>>>>>>> and has a >>>>>>>>>>>>>>>>>>>> 200 second time constant. It will take many tau before >>>>>>>>>>>>>>>>>>>> the >>>>>>>>>>>>>>>>>>>> voltage >>>>>>>>>>>>>>>>>>>> gets low enough for people to poke around inside. >>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>> The ideal discharger would be a constant-current or even >>>>>>>>>>>>>>>>>>>> better a >>>>>>>>>>>>>>>>>>>> constant-power load, all the way down to zero volts. It >>>>>>>>>>>>>>>>>>>> would be dumb, >>>>>>>>>>>>>>>>>>>> not switched by some decision circuit or anything fancy >>>>>>>>>>>>>>>>>>>> like that. >>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>> And of course we need several LEDs as warnings that the >>>>>>>>>>>>>>>>>>>> thing is hot. >>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> What sort of design needs 0.2 Farad cap, at 200 >>>>>>>>>>>>>>>>>>> volts ?. If >>>>>>>>>>>>>>>>>>> you are >>>>>>>>>>>>>>>>>>> working at that level, put in a cheap relay and a rated >>>>>>>>>>>>>>>>>>> heatsink >>>>>>>>>>>>>>>>>>> wirewound resistor to dump the energy, when the power >>>>>>>>>>>>>>>>>>> goes off. >>>>>>>>>>>>>>>>>>> Cheap, and lossless as well. Motor drive inverters >>>>>>>>>>>>>>>>>>> often have >>>>>>>>>>>>>>>>>>> big resistors to brake the motor. >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>> John Larkin >>>>>>>>>>>>>>>>>>>> Highland Tech Glen Canyon Design Center >>>>>>>>>>>>>>>>>>>> Lunatic Fringe Electronics >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> It's a 1500 amp laser driver. >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> The input to our box is DC, from an external power supply. >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> I do want a circuit that's foolproof, that always >>>>>>>>>>>>>>>>>> discharges >>>>>>>>>>>>>>>>>> the caps >>>>>>>>>>>>>>>>>> but doen't often go up in flames. >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> A resistor makes an exponential decay which could be a very >>>>>>>>>>>>>>>>>> long time >>>>>>>>>>>>>>>>>> to get down to safe levels. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> But a resistor plus an inductor could give a critically >>>>>>>>>>>>>>>>> damped >>>>>>>>>>>>>>>>> decay, >>>>>>>>>>>>>>>>> which would be quite a bit faster. I don't know enough about >>>>>>>>>>>>>>>>> the circuit >>>>>>>>>>>>>>>>> to be prepared to try to work out how much inductance you'd >>>>>>>>>>>>>>>>> need, and >>>>>>>>>>>>>>>>> you clearly can't be bothered. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> Won't be bothered. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> I thought the group might like a circuit design problem >>>>>>>>>>>>>>>>>> once >>>>>>>>>>>>>>>>>> in a >>>>>>>>>>>>>>>>>> while, a break from politics. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> But you don't do circuit design, and this sort of question >>>>>>>>>>>>>>>>> makes it >>>>>>>>>>>>>>>>> obvious why you don't. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> The inductor suggestion is hilarious. Thanks. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> It's elementary circuit theory, which you should have been >>>>>>>>>>>>>>> taught and I >>>>>>>>>>>>>>> had to read about. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> If you discharge a capacitor through a resistor, the >>>>>>>>>>>>>>> voltage decays >>>>>>>>>>>>>>> exponentially. If you put an inductor in series with the >>>>>>>>>>>>>>> resistor the >>>>>>>>>>>>>>> voltage decay is a more complicated function of time. If you >>>>>>>>>>>>>>> chose the >>>>>>>>>>>>>>> resistance and the inductance to create a critically damped >>>>>>>>>>>>>>> circuit, the >>>>>>>>>>>>>>> voltage across the capacitor will eventually decay more >>>>>>>>>>>>>>> rapidly >>>>>>>>>>>>>>> than >>>>>>>>>>>>>>> you'd see with just the resistor. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Try reading about Laplace transforms. That's a pretty >>>>>>>>>>>>>>> hilarious >>>>>>>>>>>>>>> suggestion to direct at you, but you are the butt of the joke. >>>>>>>>>>>>>> >>>>>>>>>>>>>> Oh, RLC circuits are no mystery. >>>>>>>>>>>>>> >>>>>>>>>>>>>> What's funny about the suggestion is the size of the >>>>>>>>>>>>>> inductor it >>>>>>>>>>>>>> would >>>>>>>>>>>>>> need. >>>>>>>>>>>>> >>>>>>>>>>>>> Which you haven't worked out. I spent a few minutes last night >>>>>>>>>>>>> trying to >>>>>>>>>>>>> work out what I could buy off the shelf from element-14 (the >>>>>>>>>>>>> Australian >>>>>>>>>>>>> branch of Newark) but their web-site has turned cranky in recent >>>>>>>>>>>>> months. >>>>>>>>>>>>> >>>>>>>>>>>>> The value of the inductance isn't fixed - that and the resistor >>>>>>>>>>>>> can be >>>>>>>>>>>>> be chosen to get a critically damped LCR, and I figured that I'd >>>>>>>>>>>>> start >>>>>>>>>>>>> playing with an inductor I could buy. >>>>>>>>>>>>> >>>>>>>>>>>>> You might end up with a non-progressively wound air-cored >>>>>>>>>>>>> toroid. >>>>>>>>>>>>> With a >>>>>>>>>>>>> 0.2F capacitor the parallel capacitance of the inductor isn't >>>>>>>>>>>>> going to >>>>>>>>>>>>> be an issue, and the winding resistance could be your damping >>>>>>>>>>>>> resistor. >>>>>>>>>>>>> >>>>>>>>>>>>> 4kJ is a fair bit of energy, but you can get copper quite hot >>>>>>>>>>>>> before it >>>>>>>>>>>>> explodes. It wouldn't stay hot for long. >>>>>>>>>>>>> >>>>>>>>>>>> >>>>>>>>>>>> I haven’t calculated what ballpark inductance might be >>>>>>>>>>>> required but >>>>>>>>>>>> is air >>>>>>>>>>>> core even feasible for that? >>>>>>>>>>> >>>>>>>>>>> If it were about the size of a truck maybe. >>>>>>>>>>> >>>>>>>>>>> You can estimate the inductance in your head. To discharge 0.2F >>>>>>>>>>> in, >>>>>>>>>>> say 100 seconds, you need 500 ohms. That would of course be the >>>>>>>>>>> tau of >>>>>>>>>>> an exponential decay. Adding an inductor would crisp that up. >>>>>>>>>>> >>>>>>>>>>> R*C = 100 seconds so we want L/R to be in that ballpark. >>>>>>>>> >>>>>>>>> 100 seconds is a lot too long from a safety point of view >>>>>>>>> >>>>>>>>>>> So L is around 50,000 H. >>>>>>>>> >>>>>>>>> If you start at the wrong end. >>>>>>>>> >>>>>>>>>>> Check Digikey for that. >>>>>>>>>> >>>>>>>>>> Critical damping happens when the expression for the impedance of >>>>>>>>>> the series RLC has two identical roots. This happens when L = >>>>>>>>>> R^2C/4, >>>>>>>>>> near enough, so L should be 12.5 kH. >>>>>>>>> >>>>>>>>> You can vary both L and R. A much shorter time constant means a much >>>>>>>>> smaller inductor >>>>>>>>> >>>>>>>>> I dug out my copy of Grover and thought about a 5H air-cored >>>>>>>>> inductor. >>>>>>>>> >>>>>>>>> 5H - a 1 sec time constant - would be practicable - but big. You'd >>>>>>>>> need a great deal of copper wire to make it work. >>>>>>>>> >>>>>>>>> It might be worth thinking about an iron-cored inductor. We are >>>>>>>>> looking at a fairly slow event so the current induced in the iron >>>>>>>>> would be just one more dissipation mode. >>>>>>>>> >>>>>>>>> 0.5H might work. The time constant of 0.32 sec means that your 4kJ >>>>>>>>> looks like 13kW while it is dissipating, but it would be being >>>>>>>>> dissipated in what could be a fairly substantial resistor which >>>>>>>>> wouldn't warm up much and would have time to cool off. >>>>>>>>> >>>>>>>>>> With the initial voltage 200V, it will need to briefly store just >>>>>>>>>> short of 600 J. That doesn't look like a practical solution. >>>>>>>>> >>>>>>>>> Why not? Air-cored coils can store a lot of energy. If you put a lot >>>>>>>>> of current through the turns the mechanical forces eventually rip >>>>>>>>> them >>>>>>>>> apart, but that's a very different regime. >>>>>>>>> >>>>>>>> >>>>>>>> Because an air-core 12.5 kH inductor is *big*. >>>>>>> >>>>>>> As I managed to work out, after an unfortunate slip of the mind. >>>>>>> >>>>>>> 12.5KH is much bigger inductance than you would want or need. >>>>>>> 100sec to >>>>>>> discharge a capacitor is much too long. >>>>>>> >>>>>>> 5H and and 1sec makes much more sense but the air-cored inductor would >>>>>>> still be impractically large. >>>>>>> >>>>>>> A carbonyl iron core might work >>>>>>> >>>>>>> https://www.rf-microwave.com/resources/ >>>>>>> products_attachments/67aa26a4a6d8c.pdf >>>>>>> >>>>>>> would need 16000 turns of 0.5mm OD copper wire to get to 5H. That's >>>>>>> about 34 layers of wire about 2600 metres long, and the series >>>>>>> resistance would be 230R, which is too high. >>>>>>> >>>>>>> 2.5mm OD wire might work, but that's only 100 tuns per layer, and 160 >>>>>>> layers would over-fill the winding space. >>>>>>> >>>>>>> A bigger core could accommodate more turns of thicker wire, but that >>>>>>> supplier doesn't do one. >>>>>>> >>>>>>> An iron tape core would offer more nH per root turn. They are >>>>>>> commercially available and in larger sizes >>>>>>> >>>>>>> https://www.transmart.net/current-transformer-cores.html >>>>>>> >>>>>>> but the web-site isn't all that transparent, and clearly aimed at >>>>>>> sophisticated users. >>>>>> >>>>>> You ignore simple rule of thumb: energy is more efficiently stored >>>>>> in air. >>>>> >>>>> Efficiency is just the ratio of your solution to an ideal solution. >>>>> >>>>> You haven't indicated what you are comparing. >>>>> >>>>> Energy is more simply stored in an iron cored inductor because can get a >>>>> higher inductance in a given volume - the iron eventually saturates >>>>> which complicates life, and the iron would act as a shorted turn if you >>>>> gave it half a chance. >>>> >>>> Approximate formula for maximal energy stored in inductor with a gap is: >>>> >>>> E = S*B_max^2*(l_i/mu + l_g)/(2*\mu_0) >>>> >>>> where E is the energy, B_max is maximal possible induction in the core, >>>> S is surface area of the perpendicular cut through the core, l_i is >>>> average length of magnetic path in the core, l_g is effective path >>>> trough the gap, \mu is relative magnetic permeability of the core, >>>> \mu_0 is magnetic permeability of the vacuum. >>>> >>>> The formula above assumes that you can pass whatever current is >>>> needed through the winding and the only limit to current is due to >>>> core saturation. As you can see better magnetic permeability >>>> _decreases_ maximal possible energy, simply core will saturate >>>> at lower current and gap significantly increases possible energy >>>> storage. >>>> >>>> For comparison, formula for inductance is: >>>> >>>> L = N^2*S*\mu_0/(l_i/\mu + l_g) >>>> >>>> where N is number of turns and the other are as above. So design >>>> for high energy will by neccessity have lower inductance. Winding >>>> resistance is proportional to N^2, so if you need higher ratio >>>> of inductance to resistance you need to go for bigger inductor >>>> or lower stored energy. >>> >>> We all know about putting an air-gap in the magnetic path to increase >>> the energy stored at the expense of the inductance you can get out of a >>> given core. >>> >>>>>> So to get energy storage needed for critical >>>>>> damping you need inductor as big or bigger than air cored >>>>>> inductor. >>> >>> That depends on the energy you are trying to store.If you can store >>> enough energy without saturating the core, the inductor can be a lot >>> smaller than an air-cored inductor >>> >>>>> That doesn't follow. >>>> >>>> The formula above shows this clearly: removing core allows >>>> bigger B and increases l_g term. Of course, once gap it >>>> too big approximation is rather poor, but trend is clear. >>> >>> If you need to saturate the core, and it is beginning to looks as if >>> John Larkin would have to. >>> >>>>>> You need a core because otherwise winding resistance >>>>>> is likely to be too big for critical damping. >>>>> >>>>> We can all dream of superconducting wire, but all the versions I know of >>>>> stop being super-conducting at a high enough magnetic field. I once got >>>>> to clamber around the Nijmegen University's super-conducting magnet so I >>>>> know that that can be a pretty high field. >>>> >>>> Yes. And we dream of superconducting wire which needs no refrigeration. >>> >>> That depends on the application. There are jobs that can pay for the >>> refrigeration. Research magnets are the original examples, but there's >>> going to be a magnetic resonance imaging system in a hospital near you. >>> I've got one just down the street. >>> >>> High temperature super-conductors might work with just liquid nitrogen, >>> which is cheap enough, but nobody wants to keep a rack of electronics >>> submerged in liquid nitrogen. >>> >>>>>> It seems that inductor with EI core with the following dimensions >>>>>> could satisfy the needs: >>>>>> >>>>>> Surface of the central column: 200 cm^2. >>>>>> Side of cental column: 14.14 cm. >>>>>> Height of cental column: 21.21 cm. >>>>>> Width of winding window: 7.07 cm. >>>>>> Total height of core: 35.35 cm >>>>>> Total width of core: 42.42 cm >>>>>> Total volume of core: 16962.87 cm^3 >>>>>> Weight of the core: 129426.74 g >>>>>> Air gap: 1cm >>>>> >>>>> You haven't specified the core material. My guess is that you would have >>>>> to glom it together from rectangular lumps of ferrite. With that much >>>>> air-gap, the exact material wouldn't matter much. >>>> >>>> I assumed iron. What matter is maximal allowed induction. Actually >>>> AFAICS going slightly into saturation does not hurt, so I assumed >>>> operation slightly above normal limits. >>> >>> But you didn't spell out that crucial detail. >>> >>>>> https://product.tdk.com/ >>>>> >>>>> lists a bunch. >>>>> >>>>>> To get L = 5H needs 1727 turns. I get 1.43 Ohm as winding resistance. >>>>>> >>>>>> So I guess that if one really needed such an inductor it would >>>>>> be practical. But it is bulky. I am not sure if it is bigger >>>>>> than the capacitor bank, but I expect it to be heavier. >>>>> >>>>> I'd be more interested in a toroidial core wound out of iron ribbon. >>>>> >>>>> https://megatron.ch/en/produkt-kategorie/ringbandkerne-und- >>>>> schnittbandkerne/ >>>>> >>>>> Even with a high permeability (layered) iron core you'd still need quite >>>>> a few turns to get a Henry or so of inductance. >>>> >>>> As I explained, main trouble is core saturation. The approximate >>>> formula applies to toroids too. >>> >>> You didn't explain that at all in your original post, and you certainly >>> didn't specify the saturation field you had in mind. >>> >>>>> The data sheets aren't exactly helpful. >>>>> >>>>> https://megatron.ch/infocenter/AMCC_100_Datenblatt.pdf >>> >> >> This seems to be ridiculously over-complicated. It probably takes >> a couple of minutes to undo all the screws holding down the lid of the >> box. Once the voltage has fallen below 60V it is not considered >> to be hazardous according to most safety standards. >> Why do anything complicated when a very simple solution will get the >> voltage to a reasonable value in the time it takes to get the lid off? >> Using an inductor to speed up the voltage decay seems totally >> unnecessary. >> John > > Yes, the inductor idea is silly. John Larin is convinced that the inductor idea is silly - he didn't invent it so it can't be any good. > > But even 60 volts in those caps, shorted, makes a gigantic bang. > > All I need is a simple, ultra-reliable circuit to discharge the caps > to zero volts in under two minutes. And a saturating inductor would probably do it (after it came out of saturation). > And a lot of LEDs to show when it's not done. More demanding. You don't want the LEDs lit in normal operation. You might power them from a winding on the discharge inductor. -- Bill Sloman, Sydney
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| From | john larkin <jl@glen--canyon.com> |
|---|---|
| Date | 2026-09-14 08:24 -0700 |
| Message-ID | <db4gall0m4ehpdociif2p6ll5q6c5gidkq@4ax.com> |
| In reply to | #747710 |
On Mon, 14 Sep 2026 16:18:14 +1000, Bill Sloman <bill.sloman@ieee.org> wrote: >On 14/09/2026 5:08 am, john larkin wrote: >> On Sun, 13 Sep 2026 19:40:33 +0100, John R Walliker >> <jrwalliker@gmail.com> wrote: >> >>> On 13/09/2026 17:05, Bill Sloman wrote: >>>> On 13/09/2026 11:36 pm, Waldek Hebisch wrote: >>>>> Bill Sloman <bill.sloman@ieee.org> wrote: >>>>>> On 13/09/2026 10:27 am, Waldek Hebisch wrote: >>>>>>> Bill Sloman <bill.sloman@ieee.org> wrote: >>>>>>>> >>>>>>>> >>>>>>>> On 10/09/2026 7:10 am, Jeroen Belleman wrote: >>>>>>>>> On 9/9/26 17:32, Bill Sloman wrote: >>>>>>>>>> On 9/09/2026 10:25 pm, Jeroen Belleman wrote: >>>>>>>>>>> On 9/9/26 12:44, john larkin wrote: >>>>>>>>>>>> On Wed, 9 Sep 2026 09:51:57 -0000 (UTC), piglet >>>>>>>>>>>> <erichpwagner@hotmail.com> wrote: >>>>>>>>>>>> >>>>>>>>>>>>> Bill Sloman <bill.sloman@ieee.org> wrote: >>>>>>>>>>>>>> On 9/09/2026 5:56 am, john larkin wrote: >>>>>>>>>>>>>>> On Wed, 9 Sep 2026 03:09:41 +1000, Bill Sloman >>>>>>>>>>>>>>> <bill.sloman@ieee.org> >>>>>>>>>>>>>>> wrote: >>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> On 9/09/2026 1:00 am, john larkin wrote: >>>>>>>>>>>>>>>>> On Tue, 8 Sep 2026 17:35:24 +1000, Bill Sloman >>>>>>>>>>>>>>>>> <bill.sloman@ieee.org> >>>>>>>>>>>>>>>>> wrote: >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> On 8/09/2026 4:52 am, john larkin wrote: >>>>>>>>>>>>>>>>>>> On Mon, 7 Sep 2026 19:33:35 +0100, chrisq >>>>>>>>>>>>>>>>>>> <syseng@gfsys.co.uk> wrote: >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>> On 9/7/26 16:18, john larkin wrote: >>>>>>>>>>>>>>>>>>>>> Suppose we have a box with some big caps inside, for >>>>>>>>>>>>>>>>>>>>> example 0.2 >>>>>>>>>>>>>>>>>>>>> farads that run at about 200 volts. When AC power is off, >>>>>>>>>>>>>>>>>>>>> we want to >>>>>>>>>>>>>>>>>>>>> discharge them for several reasons. >>>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>>> Putting, say, a 1K resistor across them dissipates 40 >>>>>>>>>>>>>>>>>>>>> watts >>>>>>>>>>>>>>>>>>>>> and has a >>>>>>>>>>>>>>>>>>>>> 200 second time constant. It will take many tau before >>>>>>>>>>>>>>>>>>>>> the >>>>>>>>>>>>>>>>>>>>> voltage >>>>>>>>>>>>>>>>>>>>> gets low enough for people to poke around inside. >>>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>>> The ideal discharger would be a constant-current or even >>>>>>>>>>>>>>>>>>>>> better a >>>>>>>>>>>>>>>>>>>>> constant-power load, all the way down to zero volts. It >>>>>>>>>>>>>>>>>>>>> would be dumb, >>>>>>>>>>>>>>>>>>>>> not switched by some decision circuit or anything fancy >>>>>>>>>>>>>>>>>>>>> like that. >>>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>>> And of course we need several LEDs as warnings that the >>>>>>>>>>>>>>>>>>>>> thing is hot. >>>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>> What sort of design needs 0.2 Farad cap, at 200 >>>>>>>>>>>>>>>>>>>> volts ?. If >>>>>>>>>>>>>>>>>>>> you are >>>>>>>>>>>>>>>>>>>> working at that level, put in a cheap relay and a rated >>>>>>>>>>>>>>>>>>>> heatsink >>>>>>>>>>>>>>>>>>>> wirewound resistor to dump the energy, when the power >>>>>>>>>>>>>>>>>>>> goes off. >>>>>>>>>>>>>>>>>>>> Cheap, and lossless as well. Motor drive inverters >>>>>>>>>>>>>>>>>>>> often have >>>>>>>>>>>>>>>>>>>> big resistors to brake the motor. >>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>>> John Larkin >>>>>>>>>>>>>>>>>>>>> Highland Tech Glen Canyon Design Center >>>>>>>>>>>>>>>>>>>>> Lunatic Fringe Electronics >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> It's a 1500 amp laser driver. >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> The input to our box is DC, from an external power supply. >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> I do want a circuit that's foolproof, that always >>>>>>>>>>>>>>>>>>> discharges >>>>>>>>>>>>>>>>>>> the caps >>>>>>>>>>>>>>>>>>> but doen't often go up in flames. >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> A resistor makes an exponential decay which could be a very >>>>>>>>>>>>>>>>>>> long time >>>>>>>>>>>>>>>>>>> to get down to safe levels. >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> But a resistor plus an inductor could give a critically >>>>>>>>>>>>>>>>>> damped >>>>>>>>>>>>>>>>>> decay, >>>>>>>>>>>>>>>>>> which would be quite a bit faster. I don't know enough about >>>>>>>>>>>>>>>>>> the circuit >>>>>>>>>>>>>>>>>> to be prepared to try to work out how much inductance you'd >>>>>>>>>>>>>>>>>> need, and >>>>>>>>>>>>>>>>>> you clearly can't be bothered. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> Won't be bothered. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> I thought the group might like a circuit design problem >>>>>>>>>>>>>>>>>>> once >>>>>>>>>>>>>>>>>>> in a >>>>>>>>>>>>>>>>>>> while, a break from politics. >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> But you don't do circuit design, and this sort of question >>>>>>>>>>>>>>>>>> makes it >>>>>>>>>>>>>>>>>> obvious why you don't. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> The inductor suggestion is hilarious. Thanks. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> It's elementary circuit theory, which you should have been >>>>>>>>>>>>>>>> taught and I >>>>>>>>>>>>>>>> had to read about. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> If you discharge a capacitor through a resistor, the >>>>>>>>>>>>>>>> voltage decays >>>>>>>>>>>>>>>> exponentially. If you put an inductor in series with the >>>>>>>>>>>>>>>> resistor the >>>>>>>>>>>>>>>> voltage decay is a more complicated function of time. If you >>>>>>>>>>>>>>>> chose the >>>>>>>>>>>>>>>> resistance and the inductance to create a critically damped >>>>>>>>>>>>>>>> circuit, the >>>>>>>>>>>>>>>> voltage across the capacitor will eventually decay more >>>>>>>>>>>>>>>> rapidly >>>>>>>>>>>>>>>> than >>>>>>>>>>>>>>>> you'd see with just the resistor. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> Try reading about Laplace transforms. That's a pretty >>>>>>>>>>>>>>>> hilarious >>>>>>>>>>>>>>>> suggestion to direct at you, but you are the butt of the joke. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Oh, RLC circuits are no mystery. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> What's funny about the suggestion is the size of the >>>>>>>>>>>>>>> inductor it >>>>>>>>>>>>>>> would >>>>>>>>>>>>>>> need. >>>>>>>>>>>>>> >>>>>>>>>>>>>> Which you haven't worked out. I spent a few minutes last night >>>>>>>>>>>>>> trying to >>>>>>>>>>>>>> work out what I could buy off the shelf from element-14 (the >>>>>>>>>>>>>> Australian >>>>>>>>>>>>>> branch of Newark) but their web-site has turned cranky in recent >>>>>>>>>>>>>> months. >>>>>>>>>>>>>> >>>>>>>>>>>>>> The value of the inductance isn't fixed - that and the resistor >>>>>>>>>>>>>> can be >>>>>>>>>>>>>> be chosen to get a critically damped LCR, and I figured that I'd >>>>>>>>>>>>>> start >>>>>>>>>>>>>> playing with an inductor I could buy. >>>>>>>>>>>>>> >>>>>>>>>>>>>> You might end up with a non-progressively wound air-cored >>>>>>>>>>>>>> toroid. >>>>>>>>>>>>>> With a >>>>>>>>>>>>>> 0.2F capacitor the parallel capacitance of the inductor isn't >>>>>>>>>>>>>> going to >>>>>>>>>>>>>> be an issue, and the winding resistance could be your damping >>>>>>>>>>>>>> resistor. >>>>>>>>>>>>>> >>>>>>>>>>>>>> 4kJ is a fair bit of energy, but you can get copper quite hot >>>>>>>>>>>>>> before it >>>>>>>>>>>>>> explodes. It wouldn't stay hot for long. >>>>>>>>>>>>>> >>>>>>>>>>>>> >>>>>>>>>>>>> I haven’t calculated what ballpark inductance might be >>>>>>>>>>>>> required but >>>>>>>>>>>>> is air >>>>>>>>>>>>> core even feasible for that? >>>>>>>>>>>> >>>>>>>>>>>> If it were about the size of a truck maybe. >>>>>>>>>>>> >>>>>>>>>>>> You can estimate the inductance in your head. To discharge 0.2F >>>>>>>>>>>> in, >>>>>>>>>>>> say 100 seconds, you need 500 ohms. That would of course be the >>>>>>>>>>>> tau of >>>>>>>>>>>> an exponential decay. Adding an inductor would crisp that up. >>>>>>>>>>>> >>>>>>>>>>>> R*C = 100 seconds so we want L/R to be in that ballpark. >>>>>>>>>> >>>>>>>>>> 100 seconds is a lot too long from a safety point of view >>>>>>>>>> >>>>>>>>>>>> So L is around 50,000 H. >>>>>>>>>> >>>>>>>>>> If you start at the wrong end. >>>>>>>>>> >>>>>>>>>>>> Check Digikey for that. >>>>>>>>>>> >>>>>>>>>>> Critical damping happens when the expression for the impedance of >>>>>>>>>>> the series RLC has two identical roots. This happens when L = >>>>>>>>>>> R^2C/4, >>>>>>>>>>> near enough, so L should be 12.5 kH. >>>>>>>>>> >>>>>>>>>> You can vary both L and R. A much shorter time constant means a much >>>>>>>>>> smaller inductor >>>>>>>>>> >>>>>>>>>> I dug out my copy of Grover and thought about a 5H air-cored >>>>>>>>>> inductor. >>>>>>>>>> >>>>>>>>>> 5H - a 1 sec time constant - would be practicable - but big. You'd >>>>>>>>>> need a great deal of copper wire to make it work. >>>>>>>>>> >>>>>>>>>> It might be worth thinking about an iron-cored inductor. We are >>>>>>>>>> looking at a fairly slow event so the current induced in the iron >>>>>>>>>> would be just one more dissipation mode. >>>>>>>>>> >>>>>>>>>> 0.5H might work. The time constant of 0.32 sec means that your 4kJ >>>>>>>>>> looks like 13kW while it is dissipating, but it would be being >>>>>>>>>> dissipated in what could be a fairly substantial resistor which >>>>>>>>>> wouldn't warm up much and would have time to cool off. >>>>>>>>>> >>>>>>>>>>> With the initial voltage 200V, it will need to briefly store just >>>>>>>>>>> short of 600 J. That doesn't look like a practical solution. >>>>>>>>>> >>>>>>>>>> Why not? Air-cored coils can store a lot of energy. If you put a lot >>>>>>>>>> of current through the turns the mechanical forces eventually rip >>>>>>>>>> them >>>>>>>>>> apart, but that's a very different regime. >>>>>>>>>> >>>>>>>>> >>>>>>>>> Because an air-core 12.5 kH inductor is *big*. >>>>>>>> >>>>>>>> As I managed to work out, after an unfortunate slip of the mind. >>>>>>>> >>>>>>>> 12.5KH is much bigger inductance than you would want or need. >>>>>>>> 100sec to >>>>>>>> discharge a capacitor is much too long. >>>>>>>> >>>>>>>> 5H and and 1sec makes much more sense but the air-cored inductor would >>>>>>>> still be impractically large. >>>>>>>> >>>>>>>> A carbonyl iron core might work >>>>>>>> >>>>>>>> https://www.rf-microwave.com/resources/ >>>>>>>> products_attachments/67aa26a4a6d8c.pdf >>>>>>>> >>>>>>>> would need 16000 turns of 0.5mm OD copper wire to get to 5H. That's >>>>>>>> about 34 layers of wire about 2600 metres long, and the series >>>>>>>> resistance would be 230R, which is too high. >>>>>>>> >>>>>>>> 2.5mm OD wire might work, but that's only 100 tuns per layer, and 160 >>>>>>>> layers would over-fill the winding space. >>>>>>>> >>>>>>>> A bigger core could accommodate more turns of thicker wire, but that >>>>>>>> supplier doesn't do one. >>>>>>>> >>>>>>>> An iron tape core would offer more nH per root turn. They are >>>>>>>> commercially available and in larger sizes >>>>>>>> >>>>>>>> https://www.transmart.net/current-transformer-cores.html >>>>>>>> >>>>>>>> but the web-site isn't all that transparent, and clearly aimed at >>>>>>>> sophisticated users. >>>>>>> >>>>>>> You ignore simple rule of thumb: energy is more efficiently stored >>>>>>> in air. >>>>>> >>>>>> Efficiency is just the ratio of your solution to an ideal solution. >>>>>> >>>>>> You haven't indicated what you are comparing. >>>>>> >>>>>> Energy is more simply stored in an iron cored inductor because can get a >>>>>> higher inductance in a given volume - the iron eventually saturates >>>>>> which complicates life, and the iron would act as a shorted turn if you >>>>>> gave it half a chance. >>>>> >>>>> Approximate formula for maximal energy stored in inductor with a gap is: >>>>> >>>>> E = S*B_max^2*(l_i/mu + l_g)/(2*\mu_0) >>>>> >>>>> where E is the energy, B_max is maximal possible induction in the core, >>>>> S is surface area of the perpendicular cut through the core, l_i is >>>>> average length of magnetic path in the core, l_g is effective path >>>>> trough the gap, \mu is relative magnetic permeability of the core, >>>>> \mu_0 is magnetic permeability of the vacuum. >>>>> >>>>> The formula above assumes that you can pass whatever current is >>>>> needed through the winding and the only limit to current is due to >>>>> core saturation. As you can see better magnetic permeability >>>>> _decreases_ maximal possible energy, simply core will saturate >>>>> at lower current and gap significantly increases possible energy >>>>> storage. >>>>> >>>>> For comparison, formula for inductance is: >>>>> >>>>> L = N^2*S*\mu_0/(l_i/\mu + l_g) >>>>> >>>>> where N is number of turns and the other are as above. So design >>>>> for high energy will by neccessity have lower inductance. Winding >>>>> resistance is proportional to N^2, so if you need higher ratio >>>>> of inductance to resistance you need to go for bigger inductor >>>>> or lower stored energy. >>>> >>>> We all know about putting an air-gap in the magnetic path to increase >>>> the energy stored at the expense of the inductance you can get out of a >>>> given core. >>>> >>>>>>> So to get energy storage needed for critical >>>>>>> damping you need inductor as big or bigger than air cored >>>>>>> inductor. >>>> >>>> That depends on the energy you are trying to store.If you can store >>>> enough energy without saturating the core, the inductor can be a lot >>>> smaller than an air-cored inductor >>>> >>>>>> That doesn't follow. >>>>> >>>>> The formula above shows this clearly: removing core allows >>>>> bigger B and increases l_g term. Of course, once gap it >>>>> too big approximation is rather poor, but trend is clear. >>>> >>>> If you need to saturate the core, and it is beginning to looks as if >>>> John Larkin would have to. >>>> >>>>>>> You need a core because otherwise winding resistance >>>>>>> is likely to be too big for critical damping. >>>>>> >>>>>> We can all dream of superconducting wire, but all the versions I know of >>>>>> stop being super-conducting at a high enough magnetic field. I once got >>>>>> to clamber around the Nijmegen University's super-conducting magnet so I >>>>>> know that that can be a pretty high field. >>>>> >>>>> Yes. And we dream of superconducting wire which needs no refrigeration. >>>> >>>> That depends on the application. There are jobs that can pay for the >>>> refrigeration. Research magnets are the original examples, but there's >>>> going to be a magnetic resonance imaging system in a hospital near you. >>>> I've got one just down the street. >>>> >>>> High temperature super-conductors might work with just liquid nitrogen, >>>> which is cheap enough, but nobody wants to keep a rack of electronics >>>> submerged in liquid nitrogen. >>>> >>>>>>> It seems that inductor with EI core with the following dimensions >>>>>>> could satisfy the needs: >>>>>>> >>>>>>> Surface of the central column: 200 cm^2. >>>>>>> Side of cental column: 14.14 cm. >>>>>>> Height of cental column: 21.21 cm. >>>>>>> Width of winding window: 7.07 cm. >>>>>>> Total height of core: 35.35 cm >>>>>>> Total width of core: 42.42 cm >>>>>>> Total volume of core: 16962.87 cm^3 >>>>>>> Weight of the core: 129426.74 g >>>>>>> Air gap: 1cm >>>>>> >>>>>> You haven't specified the core material. My guess is that you would have >>>>>> to glom it together from rectangular lumps of ferrite. With that much >>>>>> air-gap, the exact material wouldn't matter much. >>>>> >>>>> I assumed iron. What matter is maximal allowed induction. Actually >>>>> AFAICS going slightly into saturation does not hurt, so I assumed >>>>> operation slightly above normal limits. >>>> >>>> But you didn't spell out that crucial detail. >>>> >>>>>> https://product.tdk.com/ >>>>>> >>>>>> lists a bunch. >>>>>> >>>>>>> To get L = 5H needs 1727 turns. I get 1.43 Ohm as winding resistance. >>>>>>> >>>>>>> So I guess that if one really needed such an inductor it would >>>>>>> be practical. But it is bulky. I am not sure if it is bigger >>>>>>> than the capacitor bank, but I expect it to be heavier. >>>>>> >>>>>> I'd be more interested in a toroidial core wound out of iron ribbon. >>>>>> >>>>>> https://megatron.ch/en/produkt-kategorie/ringbandkerne-und- >>>>>> schnittbandkerne/ >>>>>> >>>>>> Even with a high permeability (layered) iron core you'd still need quite >>>>>> a few turns to get a Henry or so of inductance. >>>>> >>>>> As I explained, main trouble is core saturation. The approximate >>>>> formula applies to toroids too. >>>> >>>> You didn't explain that at all in your original post, and you certainly >>>> didn't specify the saturation field you had in mind. >>>> >>>>>> The data sheets aren't exactly helpful. >>>>>> >>>>>> https://megatron.ch/infocenter/AMCC_100_Datenblatt.pdf >>>> >>> >>> This seems to be ridiculously over-complicated. It probably takes >>> a couple of minutes to undo all the screws holding down the lid of the >>> box. Once the voltage has fallen below 60V it is not considered >>> to be hazardous according to most safety standards. >>> Why do anything complicated when a very simple solution will get the >>> voltage to a reasonable value in the time it takes to get the lid off? >>> Using an inductor to speed up the voltage decay seems totally >>> unnecessary. >>> John >> >> Yes, the inductor idea is silly. > >John Larin is convinced that the inductor idea is silly - he didn't >invent it so it can't be any good. >> >> But even 60 volts in those caps, shorted, makes a gigantic bang. >> >> All I need is a simple, ultra-reliable circuit to discharge the caps >> to zero volts in under two minutes. > >And a saturating inductor would probably do it (after it came out of >saturation). > >> And a lot of LEDs to show when it's not done. > >More demanding. You don't want the LEDs lit in normal operation. You >might power them from a winding on the discharge inductor. Of course we want lots of red leds lit up when lethal amounts of energy are present. John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
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