Re: [TCML] Chinese made polystyrene caps

[DC Cox <resonance@xxxxxxxxxxxx>]

I tested some 100 nF units.  Yes, on an actual coil (Big Bruiser).  24 inch
dia sec, variable RSG, 1" electrodes for good quenching.

We were running at 18 kVA when they failed (2 of them).

D.C. Cox




On Wed, May 13, 2009 at 4:00 PM, Quarkster <quarkster@xxxxxxx> wrote:

> Hello DC -
>
> Since it looks like you are the only one who has performed controlled
> testing of these imported polystyrene capacitors, it would be great if you
> could share the results of your testing with the TCML.
>
> 1. What specific value (or values) of these Chinese HV polystyrene
> capacitors did you test?    (The seller is offering multiple ratings.)
>
> 2. Was your capacitor testing conducted in an actual Tesla coil tank
> circuit? Can you describe the test setup or coil parameters?
>
> 3. You mention that you found that these capacitors are NOT suitable for
> power levels greater than 5 KVA. What was the failure mode that you
> encountered when you ran them at the >5 KVA power level? Did they overheat,
> suffer internal dielectric failure, flash over externally, or experience
> some other type of failure?
>
> 4. What was the approximate peak current and voltage the capacitor(s) were
> subjected to in your testing?
>
> Any actual test data that you can provide would certainly be useful to
> uninformed Tesla coil builders who are looking for suitable tank capacitors
> and find these on eBay.
>
> Best Regards,
> Herr Zapp
>
> --- On Wed, 5/13/09, DC Cox <resonance@xxxxxxxxxxxx>
>  wrote:
> From: DC Cox <resonance@xxxxxxxxxxxx>
> Subject: Re: [TCML] Chinese made polystyrene caps
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Date: Wednesday, May 13, 2009, 10:04 AM
>
> I've tested them.  They are not up to pole xmfr standards.  Perhaps good
> below 5 kVA, but not above.
>
> Our units are more expensive at $800, but still well below the $1,700
> Maxwell price for the same unit.  Our are actually better for TC use since
> the Q factor
> is over 20,000 as compared with only 12,000 for the Maxwells.
>
> Dr. Resonance
>
>
>
>
> On Tue, May 12, 2009 at 5:42 PM, bartb <bartb@xxxxxxxxxxxxxxxx> wrote:
>
> > Hi David,
> >
> > Ditto on Gary and Matts' comments. This cap has come up before on the
> list.
> > Someones going to have to give them a try, but at $180 ea,
>  well,
>  someone
> > with a money tree in the backyard will have to do it. I suspect due to
> it's
> > small size rms currents are going to play a major role in it's
> limitation.
> > There is also a high probability that these Chinese caps are not up to
> par
> > in the derating area as is standard by major cap manufacturers. Too many
> > unknowns.
> >
> > Take care,
> > Bart
> >
> >
> > David Rieben wrote:
> >
> >> Hey guys,
> >>
> >> I was just wondering if anyone has any experience
> >> with these Chinese made capacitor types that are
> >> absolutely flooding eBay these days:
> >>
> >>
> >>
>
> http://cgi.ebay.com/30kV-0-2-F-High-Voltage-Polystyrene-capacitor-HAM-audio_W0QQitemZ360120565659QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item53d8dbbf9b&_trksid=p4634.c0.m14.l1262&_trkparms=%7C301%3A1%7C293%3A6%7C294%3A30
> >>
> >>
>  My guess is
>  that since this particular one is only
> >> 80 mm x 120 mm long or appr. 3 1/8" x 6" long, and yet it
> has a very
> >> significant energy capacity (90 J), there is no way that its internal
> >> construction could render it competant to withstand the high RMS cur-
> >> rents and tremendous peak currents encountered
> >> in larger SG driven Tesla coil circuits, even though polystyrene is a
> >> good, low loss dielectric. Likely of very fragile metallized film
> >> construction. What are
> >> your thoughts?
> >>
> >> David Rieben
> >> _______________________________________________
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> >>
> >>
> >>
> > _______________________________________________
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> >
>
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> >
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