Re: Caps DC to AC rating

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Barton B. Anderson by way of Terry Fritz <twftesla-at-uswest-dot-net>" <tesla123-at-pacbell-dot-net>

Hi Terry,

Seems we are "asking" for AC ratings in the various programs when we are
concerned with DC ratings. I think we are assuming DC ratings in the calcs. I
think the programs only require a simple label change for this particular
input.

Bart

Tesla list wrote:

> Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>
>
> Hi Kevin,
>
> At 08:58 PM 1/17/2001 +0000, you wrote:
> >In Terry’s MMC calculator, I am asked for a caps AC voltage rating. Given
> >the caps DC rating, how do I get the AC rating?
>
> The program askes for the DC voltage of each individual capacitor.  This
> value is used as the maximum peak voltage on each cap.
>
> If one has say 10000 VAC the peak is 1.414 times that or 14140 volts.
>
> Vpeak = SQRT(2) x Vac     <--- Basic important equation
>
> So if you have a 15kV transformer and 1600 volt DC caps, the peak voltage is:
>
> 15000 x 1.414 = 21213 volts
>
> The number of caps needed is 21213 / 1600 = 13.26 caps.
>
> Note that many people run the caps at a bit higher voltage to save money
> since the caps don't seem to mind.
>
> The caps are actually rated around 630 volts AC for standard poly caps but
> that rating is for full time AC use which really does not apply to us.  We
> just worry about the peak voltage where they will start to break down.
>
> I hope that is what you were asking.
>
> Cheers,
>
>         Terry
>
> >I found a few references to
> >this question in the archive. From what I could understand the AC rating
> >will be somewhat lower than the DC rating. And the caps actual AC voltage
> >rating is inversely proportional to frequency due to partial discharge and
> >properties intrinsic of the dielectric. But I couldn’t find a definite
> >equation. If anyone has an equation or at least a general guide, please post
> >it. Thanks, Kevin, thebiggiantkevin-at-hotmail-dot-com
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