Re: How could a pulse cap operate in TC?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>

HI Grishka,
            Important ratings for commercial caps in TC use include:
- % reversal (approaching 90% or more in loosely coupled coils); this
determines maximum dielectric stress where cap polarization reverses
at the resonant frequency
- Shot frequency; number of BPS which relates to RMS current
- Shot life; (average minimum) number of bangs the capacitor will
withstand
- Voltage rating; the higher the better
The list is not exhaustive but those are the ones I'd particularly
take note of.

Malcolm

On 13 Jul 2005, at 12:28, Tesla list wrote:

> Original poster: Grishka <ghome@xxxxxxxxx>
>
> Hello everybody,
> The capacitor is the most critical part in a SGTC, because it should
> withstand great power levels at rather high frequencies. Many factors
> are involved here - maximum speed of voltage increase - i. e. dV/dt,
> dielectric loses in a cap, level of its reactive power & some others.
> Many people doing rather nicy TCs are completely careless in choosing
> right capacitor (MMC) and its parameters in operation. I`ve seen many
> coilers using MMC and saying that "it`s working - so it`s OK". But
> even using a MMC we should calculate some very important details. I
> remember Terry Fritz wrote here:
>
> http://www.pupman.com/listarchives/2002/July/msg01473.html
>
> "MMC caps have a giant advantage in that they are cheap and easy to
> test under "deadly" conditions to determine exactly how "much they can
> take". Expensive commercial caps can't be tested with such wild
> abandon and we have to trust the typically "scarce" information the
> manufactures give us."
>
> What is this "information"? What exactly parameters are the most
> criticle and important for us? Now I`ve got a question about types of
> caps you use - reading some articles I found the Maxwell caps to be
> the most reliable - if I`m not mistaken they were designed to operate
> at laser applications. In such applications capacitor works in a pulse
> way with fast discharge into low-resistance load with frequencies not
> more than 100..200 Hz.
>
> Now questions:
>
> -How could a Maxwell cap work in a TC, where frequencies are hundreds
> of KHz? -Does it overheat a lot? What are the practical values for the
> dielectric loses in your caps?
>
> Maybe people, who works with high-power RF applications can give some
> advices about using capacitors in these devices?
>
>
>
>
> --
> Best regards,
>   Grishka                          mailto:ghome@xxxxxxxxx
>
>
>