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Re: [TCML] Very High Voltage Polystyrene Caps on e-bay
Bart -
It sounds like your CSI caps were probably a "customer special", and not a standard CSI catalog item.
One question: how do you know the dielectric is polystyrene, and not polyester, polypropylene, polycarbonate or some of the other "poly" materials that are used as dielectrics in special-purpose capacitors?
Regards,
Herr Zapp
--- On Thu, 9/4/08, bartb <bartb@xxxxxxxxxxxxxxxx> wrote:
From: bartb <bartb@xxxxxxxxxxxxxxxx>
Subject: Re: [TCML] Very High Voltage Polystyrene Caps on e-bay
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Date: Thursday, September 4, 2008, 8:08 PM
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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