Groups > sci.electronics.design > #748297

Re: Ferrite ID

From	Bill Sloman <bill.sloman@ieee.org>
Newsgroups	sci.electronics.design
Subject	Re: Ferrite ID
Date	2026-09-29 00:42 +1000
Organization	A noiseless patient Spider
Message-ID	<119dud3$2dlrt$1@dont-email.me> (permalink)
References	<11965md$1i$1@reader1.panix.com> <11988fm$dlpc$1@dont-email.me>

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On 26/09/2026 8:57 pm, Ian wrote:
> On 9/25/26 16:58, David Lesher wrote:
>> Rheem tankless water heaters, fed with dual 40A 240V circuits,
>> are driving all the Leviton and other brand dimmers berserk.
>> The lighting all dims and flickers beserkly. The Rheem has a
>> sharp spike at the peaks of the positive and negative cycles;
>> that is the cause.
>>
>> The cure is some ferrite chokes on the power feeds. But fields
>> class was Many Decades ago. I'm trying to decide if I want ones
>> with an ID that just accepts the #8 stranded, or it doesn't
>> matter that much if it's a loose fit.
>>
>> Thoughts?
> 
> First, need to define the rise time and shape of the spike,
> to work out how much inductance is needed to filter it, along
> with any caps at the supply side, for low pass filtering. You
> could also try separating the feed to the heater, from
> everything else, to reduce voltage drop effects. 40 amps is
> pretty high current for a domestic setup, though electric
> showers often match that, or more.
> 
> Sounds like a poor quality emc side of the design though.

Absolutely. Screwing up light dimmers is vandalism. Sticking on 
arbitrary inductance and seeing if it makes a difference is a perfectly 
respectable way of starting to get to a better engineered solution, and 
if it does stop the light dimmers from going beserk without needing all 
the work a a well-engineered solution would take, it is a cheap way to 
get there.

There's a lot to be said for a bit of quick and dirty tinkering to get a 
clearer idea of what's going on. It works a lot better if you know what 
you are doing and have the kind of diagnostic tools that let you see how 
much difference your tinkering has made, but you can get lucky.

-- 
Bill Sloman, Sydney

Thread

Ferrite ID David Lesher <wb8foz@panix.com> - 2026-09-25 15:58 +0000
  Re: Ferrite ID John R Walliker <jrwalliker@gmail.com> - 2026-09-25 17:02 +0100
  Re: Ferrite ID Bill Sloman <bill.sloman@ieee.org> - 2026-09-26 02:55 +1000
  Re: Ferrite ID john larkin <jl@htigct.com> - 2026-09-25 17:13 -0700
    Re: Ferrite ID Bill Sloman <bill.sloman@ieee.org> - 2026-09-26 16:39 +1000
      Re: Ferrite ID john larkin <jl@glen--canyon.com> - 2026-09-26 09:10 -0700
        Re: Ferrite ID Bill Sloman <bill.sloman@ieee.org> - 2026-09-27 16:32 +1000
          Re: Ferrite ID Brian Gregory <void-invalid-dead-dontuse@email.invalid> - 2026-09-28 23:30 +0100
            Re: Ferrite ID someone <2a59d59e3809f827ce709d3815e3950eef4a6a93af5557a93a7fdfba71460843@example.com> - 2026-09-29 19:15 +0000
              Re: Ferrite ID Bill Sloman <bill.sloman@ieee.org> - 2026-09-30 17:24 +1000
                Re: Ferrite ID john larkin <jl@glen--canyon.com> - 2026-09-30 07:50 -0700
                Re: Ferrite ID someone <2a59d59e3809f827ce709d3815e3950eef4a6a93af5557a93a7fdfba71460843@example.com> - 2026-09-30 20:00 +0000
        Re: Ferrite ID Bill Sloman <bill.sloman@ieee.org> - 2026-09-27 16:34 +1000
        Re: Ferrite ID someone <2a59d59e3809f827ce709d3815e3950eef4a6a93af5557a93a7fdfba71460843@example.com> - 2026-09-28 16:30 +0000
      Re: Ferrite ID someone <2a59d59e3809f827ce709d3815e3950eef4a6a93af5557a93a7fdfba71460843@example.com> - 2026-09-28 16:30 +0000
    Re: Ferrite ID someone <2a59d59e3809f827ce709d3815e3950eef4a6a93af5557a93a7fdfba71460843@example.com> - 2026-09-28 16:30 +0000
  Re: Ferrite ID Ian <devnul@blackhole.com> - 2026-09-26 11:57 +0100
    Re: Ferrite ID Bill Sloman <bill.sloman@ieee.org> - 2026-09-29 00:42 +1000
      Re: Ferrite ID Martin Rid <martin_riddle@verison.net> - 2026-09-28 11:04 -0400
        Re: Ferrite ID someone <2a59d59e3809f827ce709d3815e3950eef4a6a93af5557a93a7fdfba71460843@example.com> - 2026-10-01 04:15 +0000
      Re: Ferrite ID Ian <devnul@blackhole.com> - 2026-09-30 17:47 +0100

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