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NNTP-Posting-Date: Thu, 05 Dec 2024 17:48:20 +0000
From: Joe Gwinn <joegwinn@comcast.net>
Newsgroups: sci.electronics.design
Subject: Re: electrical deaths
Date: Thu, 05 Dec 2024 12:48:19 -0500
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On Thu, 5 Dec 2024 02:21:03 +0100, "Carlos E.R."
<robin_listas@es.invalid> wrote:

>On 2024-12-05 02:02, Joe Gwinn wrote:
>> On Wed, 4 Dec 2024 22:25:19 +0000, liz@poppyrecords.invalid.invalid
>> (Liz Tuddenham) wrote:
>> 
>>> Joe Gwinn <joegwinn@comcast.net> wrote:
>>>
>>> [...]
>>>>
>>>> Measuring winding DC resistances with probes did not work - contact
>>>> resistances too large and unstable.
>>>
>>> Feed a constant current through the winding and then measure the
>>> volt-drop with a pair of probes on the wires themselves, so that the
>>> volt-drop of the terminal contact area is not included in the reading.
>>>
>>> That is a standard four-terminal measuring technique used for low value
>>> resistance.
>> 
>> I do have a 6.5-digit bench top digital multimeter.
>> 
>> The problem was that I didn't have four hands, and clip leads were too
>> flaky as well.  All such problems were solved using the 6-bar terminal
>> strip.
>
>How about using AC from a signal generator?

I do have the equipment to that, but it wouldn't make any difference.
The contact points are tiny (very low capacitance and inductance), but
with a stuttering series contact resistance.

This was the first time I had encountered such a black-box problem to
solve.  If I had to do it again, I'd do it differently.  One thing
would be to use a small transformer to excite the windings with 24 Vac
60Hz power, and go around measuring voltages, and so on.  I developed
another method that needed only electrician skills and tools, but
don't recall the details.  But still have my notes.

Joe Gwinn