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From: john larkin <jl@glen--canyon.com>
Newsgroups: sci.electronics.design
Subject: Re: Cap C-V test
Date: Sun, 04 May 2025 12:07:28 -0700
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On Sun, 04 May 2025 18:31:20 +0100, Cursitor Doom <cd@notformail.com>
wrote:

>On Sun, 04 May 2025 07:27:55 -0700, john larkin <jl@glen--canyon.com>
>wrote:
>
>>On 4 May 2025 11:17:07 GMT, Michael Schwingen
>><news-1513678000@discworld.dascon.de> wrote:
>>
>>>On 2025-05-04, john larkin <jl@glen--canyon.com> wrote:
>>>>
>>>> Two of those caps in series would make about half the capacitance of
>>>> two in parallel, but ESR and ESL would suffer by 4:1.
>>>
>>>Not really - according to your measurements, at 25V, the caps should have
>>>about 1.46uF, so the series combination has 0.73uF instead of the 0.83uF of
>>>the parallel combination.
>>>
>>>cu
>>>Michael
>>
>>One cap is .83 at 50 volts. Two in parallel would be 1.66.
>>
>>The series pair is about .73 as you note. That assumes that the DC
>>voltage divides equally.
>>
>>Ceramic cap nonlinearity is weird. To get the most C, is it always
>>better to pick the cap with the highest nameplate capacitance?
>>
>>Some caps are 1/5 their rated C at their rated voltage. Bad for timing
>>circuits.
>
>Essential to test 'em then! Are you really getting SRFs as low as just
>a few K?

I wasn't measuring SRF. I eyeballed the -3 dB point where the cap
impedance was 50 ohms.

Maybe 1 nH and 2.2 uF would have its SRF null around 3 MHz.