Re: Cap C-V test

On 4 May 2025 16:46:05 GMT, Michael Schwingen
<news-1513678000@discworld.dascon.de> wrote:

On 2025-05-04, john larkin <jl@glen--canyon.com> wrote:

>
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.

>
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.

>
Upps, yes. Must have been lack of coffee.
>

Ceramic cap nonlinearity is weird. To get the most C, is it always
better to pick the cap with the highest nameplate capacitance?

>
Not sure.  In one case where I needed about 9uF at 12V DC, standard X5R/X7R
22uF/25V all came out at about 7.5uF, and 22uF/35V were not a bit better.

Maybe most ceramics have similar volumetric energy storage?

>
IIRC, X7S performed much better.
>
Murata Simsurfing has typical Capacitance/DC bias curves for all their parts.

That's unusual. The Venkel data sheet has gobs of temperature curves
and doesn't even mention voltage effects.

>
cu
Michael