Groups > sci.electronics.design > #458617

Re: DC current sources

From	mike <ham789@netzero.net>
Newsgroups	sci.electronics.design
Subject	Re: DC current sources
Date	2017-05-03 13:22 -0700
Organization	A noiseless patient Spider
Message-ID	<oede2t$pu9$1@dont-email.me> (permalink)
References	<5909c9eb$0$34631$b1db1813$15bdbe48@news.astraweb.com>

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On 5/3/2017 5:15 AM, Clifford Heath wrote:
> A friend works in concrete reinforcing corrosion remediation,
> and has been asked to take over a project that's underway
> despite not having been properly designed or specified.

That's the key!  Not properly designed or specified.
Hard to design a solution when you don't understand the problem.
>
> The contractors are installing 400 anodes into the structure,
> and each one needs a specific amount of charge to be deposited
> into it, all over a week or two. The resistance is unknown and
> could change from day to day, but the voltage must not rise
> above +9V, or the titanium wires rapidly corrode. So they
> want to adjust the current for each anode, probably in the
> range of 100ma to 3000mA. They're intending to feed the whole
> protection thing from banks of 12V lead acid batteries, I
> guess because it's a remote site.

Am I the only one who thinks that 1200 amps for two weeks
is a lot to expect from batteries at a remote site?
>
> The initial thought was to walk around and measure the current
> on each anode every day, and switch off any that have dumped
> the required charge... but that's quite labour-intensive.

Since we have an unspecified problem, how about a random answer?
Consider a plating process with a limited amount of source
material.  It takes a specific number of electrons to use up
all the material.  Then the plating, and current, stops.
It's the same process used in the old-style mercury timers
for equipment usage...or a battery.
Use a 6V battery to limit the voltage.
If you think the current may exceed the 3A, use an incandescent
light bulb in series to limit the current.  Also gives you visual
fault location.
Or just size the plating electrodes to limit current.
The actual design of the plating cells is currently "unspecified".
How many sites need 400 of them?  Might be a market opportunity.

Or maybe build 400 Brown's gas generators.  Water level drops
as gas is generated.  Don't know the number of electrons so
may not be able to gauge the water level accurately.
Might have to use the gas to displace different water to gauge
the electrons delivered.  Something akin to a manometer.  It's all about 
the numbers.
But you can burn the Brown's gas to get back some of the power
wasted. ;-)

Or maybe one resistor (with a diode across it) feeding a 400-way
switch from an 8V battery.
Every hour, turn off current to all the anodes.  Cycle thru
all 400, logging individual currents and integrating.
Then turn the ones that have not reached terminal charge back on.
It's not like they'll be changing rapidly.
Bluetooth to a phone for readout.  If you have control
of the programmer/logger end, I'd use serial IR and something
like an old Palm Pilot.  Wouldn't expect current phones to
support that.
There may be better methods, but PICbasic could make all that
work in an hour.  400 transistors or relays and a 400-bit
shift register might take longer.  That system segments/scales well.

Or maybe something akin to 400 buck converters.
Charge a cap. Discharge it into the anode.
You know how many cycles required to deliver the required
charge. Count them.  Use a smoothing cap at the anode
and limit the cycle frequency to limit the average current.
8-pin microcontroller programmed by serial port to stop
after delivering required number of electrons.

I haven't seen any mention of fault tolerance.  How critical is
that total charge number?   What happens when someone trips
over the cable and interrupts power?  Microcontroller addresses that.

Bottom line...if you want to measure electrons delivered,
design a tool based on that process. The devil is in the details.

>
> So I was thinking about current regulators. What's the easiest
> way of sourcing 400 adjustable DC current sources in a short time?
>
> I was thinking of LM350T regulators, programmed with a power
> resistor in the range 0.6-10 ohms... but the 2degC/W heat sink
> for each one could be an issue (thinking 2A, 14.7V, shorted to
> earth; 30W).
>
> Is there any other off-the-shelf quick solution that comes to
> mind?
>
> Clifford Heath.

Thread

DC current sources Clifford Heath <no.spam@please.net> - 2017-05-03 22:15 +1000
  Re: DC current sources George Herold <gherold@teachspin.com> - 2017-05-03 05:55 -0700
    Re: DC current sources "Ian Field" <gangprobing.alien1@virginmedia.com> - 2017-05-03 19:40 +0100
      Re: DC current sources tabbypurr@gmail.com - 2017-05-06 00:39 -0700
  Re: DC current sources Martin Brown <'''newspam'''@nezumi.demon.co.uk> - 2017-05-03 14:06 +0100
    Re: DC current sources Winfield Hill <hill@rowland.harvard.edu> - 2017-05-03 11:06 -0700
      Re: DC current sources "Ian Field" <gangprobing.alien1@virginmedia.com> - 2017-05-03 19:43 +0100
        Re: DC current sources Winfield Hill <hill@rowland.harvard.edu> - 2017-05-03 13:02 -0700
          Re: DC current sources Winfield Hill <hill@rowland.harvard.edu> - 2017-05-03 17:22 -0700
        Re: DC current sources tabbypurr@gmail.com - 2017-05-06 00:41 -0700
  Re: DC current sources "dcaster@krl.org" <dcaster@krl.org> - 2017-05-03 06:15 -0700
  Re: DC current sources Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> - 2017-05-03 11:10 -0400
  Re: DC current sources Tim Wescott <tim@seemywebsite.com> - 2017-05-03 11:27 -0500
    Re: DC current sources "Ian Field" <gangprobing.alien1@virginmedia.com> - 2017-05-03 19:47 +0100
      Re: DC current sources Clifford Heath <no.spam@please.net> - 2017-05-04 12:41 +1000
        Re: DC current sources "Ian Field" <gangprobing.alien1@virginmedia.com> - 2017-05-04 20:55 +0100
          Re: DC current sources Clifford Heath <no.spam@please.net> - 2017-05-05 08:39 +1000
  Re: DC current sources "dcaster@krl.org" <dcaster@krl.org> - 2017-05-03 09:37 -0700
  Re: DC current sources Tim Wescott <seemywebsite@myfooter.really> - 2017-05-03 13:53 -0500
    Re: DC current sources Clifford Heath <no.spam@please.net> - 2017-05-04 12:24 +1000
      Re: DC current sources mike <ham789@netzero.net> - 2017-05-04 00:48 -0700
      Re: DC current sources whit3rd <whit3rd@gmail.com> - 2017-05-04 14:09 -0700
        Re: DC current sources Clifford Heath <no.spam@please.net> - 2017-05-05 08:42 +1000
  Re: DC current sources mike <ham789@netzero.net> - 2017-05-03 13:22 -0700
  Re: DC current sources whit3rd <whit3rd@gmail.com> - 2017-05-03 13:25 -0700
    Re: DC current sources Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-05-03 13:45 -0700
      Re: DC current sources whit3rd <whit3rd@gmail.com> - 2017-05-03 15:40 -0700
        Re: DC current sources Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-05-03 16:04 -0700
      Re: DC current sources krw@notreal.com - 2017-05-03 21:26 -0400
    Re: DC current sources Clifford Heath <no.spam@please.net> - 2017-05-04 12:27 +1000
  Re: DC current sources John Robertson <spam@flippers.com> - 2017-05-03 22:48 -0700
    Re: DC current sources Clifford Heath <no.spam@please.net> - 2017-05-04 16:36 +1000
  Re: DC current sources Jasen Betts <jasen@xnet.co.nz> - 2017-05-04 04:59 +0000
    Re: DC current sources Chris Jones <lugnut808@spam.yahoo.com> - 2017-05-04 22:50 +1000
    Re: DC current sources tabbypurr@gmail.com - 2017-05-06 00:53 -0700
  Re: DC current sources John Robertson <spam@flippers.com> - 2017-05-03 23:38 -0700
    Re: DC current sources Clifford Heath <no.spam@please.net> - 2017-05-04 16:45 +1000
      Re: DC current sources John Robertson <spam@flippers.com> - 2017-05-04 11:16 -0700
    Re: DC current sources Winfield Hill <hill@rowland.harvard.edu> - 2017-05-04 14:32 -0700
      Re: DC current sources "Ian Field" <gangprobing.alien1@virginmedia.com> - 2017-05-05 20:21 +0100
      Re: DC current sources Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-05-06 05:59 -0700
        Re: DC current sources Steve Wilson <no@spam.com> - 2017-05-06 14:04 +0000
  Re: DC current sources Robert Baer <robertbaer@localnet.com> - 2017-05-04 19:32 -0800
    Re: DC current sources mike <ham789@netzero.net> - 2017-05-05 00:18 -0700
      Re: DC current sources Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2017-05-05 08:28 +0000
        Re: DC current sources Robert Baer <robertbaer@localnet.com> - 2017-05-05 22:09 -0800
          Re: DC current sources Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2017-05-06 06:17 +0000
            Re: DC current sources Robert Baer <robertbaer@localnet.com> - 2017-05-06 20:47 -0800
              Re: DC current sources Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2017-05-07 08:27 +0000
      Re: DC current sources Robert Baer <robertbaer@localnet.com> - 2017-05-05 22:07 -0800

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