RE: Cap Question

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

Original poster: "Vanderputten, Gary by way of Terry Fritz <twftesla-at-qwest-dot-net>" <gvp-at-pvaintl-dot-com>

I think this whole cap discussion underscores why this List is so fantastic.
There is no finite answer to the cap issue for everyone, and performance,
money, availability and chance all enter into the equation. I just live the
variations. For a modest 1000w coil, I built an MMC with six 10kv/.01mf caps
(about 6" x1.5") that I bought on ebay last spring. The discussion on these
particular caps in the List went from the curious to the highly opinionated
and worse. 'They'll heat up and explode.' By following the List's
recommendations for cap size and protection with respect to tranny size, I
packaged a 30kv/.006 cap for a 12/60 setup. Runs great. Never even gets
warm. Even tried a 15/60 for a short while. Costs $30 for the 6 of them.
Easy to package up. Neat, cheap, and simple to work with. 

Informed resourcefulness!

Gary

 -----Original Message-----
From: 	Tesla list [mailto:tesla-at-pupman-dot-com] 
Sent:	Thursday, April 04, 2002 1:14 AM
To:	tesla-at-pupman-dot-com
Subject:	Re: Cap Question

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