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

[bartb <bartb@xxxxxxxxxxxxxxxx>]

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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