Re: Cap Question

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

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "Christopher Boden by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <chrisboden-at-hotmail-dot-com>
> 
> >Original poster: "Soul Firez by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> ><soul_firez-at-hotmail-dot-com>
> >
> >
> >Hey,
> >Im looking for capps on ebay and i keep seeing doornob caps and big oil
> >caps
> >(the ones in the big cans with the terminals on top) and i was wonderring
> >if
> >these would be appropriat for coil use?
> 
> Some are, yes. Doorknobs tend to drift in value as they heat up, and also
> crack. They don't tolerate overvoltage too terribly well either. The big
> metal cans are usually industrial PFC caps and unsuitable for coiling (you
> need HV Pulse caps). Even if the cap is of the right type and voltage, in
> coiling (where overvoltage of the cap is quite common, especially among
> newbie coilers) those nice big metal pulse caps almost universally become
> nice big metal doorstops in what is never a long enough lifespan :) The cap
> could last you for 5 years, or 5 minutes, you have no way of knowing.

	I have been using Sprague 0.004 ufd, 20 kV filter "doorknobs" for
several years with good results, PROVIDED I don't run them long enough
to "warm up much".  They're lossy, but have low series resistance which
counts for more.  I'm using 3 in parallel with a 12 kV, 60 ma
transformer and have found that  60 second runs seem OK.  Blew some when
I first started out, but after I tried runs of different lengths and
observing how fast they got hot, I arrived at the minute maximum and
haven't lost one since.

	No where near as rugged as the MMC's, but a lot easier to use when
you're first starting up.

Ed