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Re: [TCML] Very High Voltage Polystyrene Caps on e-bay



Gary, in this case the terminations are interesting (as if a screw is inserted on these caps in their end plates). Looks like the end caps are thread nuts of a sort. Promising from that view.

And from a "puny" view, I have to tell you that I have been using polystyrene caps for 10 years now with no warmth, failure, or even performance degradation. But my caps are 20nF, 60kV, and maybe a bit special. The caps are cylinder shaped and 3" diameter x 16.5"L with a huge 3/8" brass threaded rod protruding about 1.5" out of each end. Even the nuts are silver plated. These were made by CSI (I have 3 of them). So nothing puny there as their obviously built for high current.

It's the mechanical internal construction that is really in question with the caps Greg listed. I did note that some of the other caps the seller had were similar, but those had leads as part of the construction. However, the cap Greg listed were like threaded inserts at each end. The leads would probably be fine, but it was interesting to see no leads on this particular cap.

Bart

Lau, Gary wrote:
I agree with everything that Bart said.  But, all of the polystyrene caps that I gave seen (I have not looked extensively) have had very puny end terminations.  I think that polystyrene caps are mainly used tor temperature stability, as opposed to high current capability.

Regards, Gary Lau
MA, USA

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of bartb
Sent: Thursday, September 04, 2008 9:21 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] Very High Voltage Polystyrene Caps on e-bay

Hi Greg,

Yes, polystyrene is excellent for high frequency pulse caps. These caps
might be ok, but they are an unknown and a risk until some tries them
and reports back. There's no telling what the internal end construction
is like. The power dissipation is my biggest worry (it is a rather small
cap, so the power cannot be distributed across a string as it could with
say 15 of the CD 0.15uF caps needed to achieve the same value). There
are some unknowns, but nothing really stands out as a show stopper,
expect maybe the price (a string of CD caps to make the same value would
cost less). So price and the fact that it's an unknown is the risk. The
dielectric itself fine.

Bart


G Hunter wrote:
There's a whole page of these oddballs on e-bay of various sizes and voltage
ratings:
http://cgi.ebay.com/50kV-10nF-High-Voltage-Polystyrene-capacitor-HAM-
audio_W0QQitemZ150269299882QQcmdZViewItem?hash=item150269299882&_t
rkparms=72%3A552%7C39%3A1%7C66%3A2%7C65%3A12%7C240%3A1318&_
trksid=p3286.c0.m14
Polystyrene is one of the "good" pulse cap dielectrics, right?  I wonder if one of
these might be suitabe for a tabletop TC?  Anybody ever tried one?  If not pulse
duty, then what are these good for?
Greg

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