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Re: Success with PP Multi-Mini Cap

Hello Ed & Ed, all,

>Original Poster: Esondrmn-at-aol-dot-com
>
>In a message dated 3/29/99 2:13:07 AM Pacific Standard Time,
tesla-at-pupman-dot-com
>writes:
>
>>  As I mentioned a few days ago, I have had some encouraging results
with a
>>  > new tank capacitor made from a series/parallel array of small
.015uF
>>  > 1.6KVDC polypropylene commercial caps.  Briefly, I used series
strings of
>>  > sixteen of the caps for an effective DC voltage rating of 25.6KV,
with a
>>  > 15KV-RMS/60mA NST power supply.
>>  >


>>  Gary:
>>
>>          Very interesting.  How much do the individual capacitors
cost and
>> where
>>  did you get them?
>>  Ed


>
>Are these cap strings submerged in oil?
>
>Ed Sonderman
>

As I am to using an MMC too, maybe I can shed a little light here.

To Ed Philips:
I bought my caps from surplus. They are new, however. They come
from a defunct german manufacturer. I paid 28pf (or 16 cents) for
each. Just like Gary, I was tired of blowing PE caps and messing
around with oil. A 100nF 30kV (AC) pulse cap cost around $3000,
over here. TC´ing is supposed to be a hobby and not a rip-off, so
I can´t buy a commercial pulse cap. I bought (first order) 200 of
the MKP caps. They are pretty large for their rating (62nF-at-
1kV DC). They are 0.5" thick, 1 1/2" wide and 1 1/4" high. My
present setup runs them at peak AC = DC rating and they have
clocked at least 1hrs (total) run time. There are no signs of
heating and the TC spark length hasn´t deteriorated either.
I am running them without a safety cap (across the caps) and
no equalization resistors. The MMC is THE best cap I have ever
built (and I have tried a few designs). I am also using a set
of Japanese caps (Taitsu) rated at 18nF and 1600Vdc (each)
with great sucess. These, too, are large in size. I tried a set
of Philips X2-MKP (Series 336-2) supressor caps. I was hoping
these would be ideal for TC usage. However, forget it!! They are
very small for their rating (330nF-at-250VAC (!)). Size: 3/8" thick,
1" wide and 3/4" high. I used 35 in series in my 7.5kV NST coil.
They lasted for about 15-20 secs and then quit their job... (;o((.
Philips rates their maximum voltage (short pulse) at 2100Vac. NO
WAY!!! I believe the small size and the fact that they use
metalized plastic end plates are what lead to their failure. Gary
Lau´s caps and mine use metal foil (!) as electrodes. The plastic
junk probably can´t withstand the high pulse currents involved in
TC usage.


To Ed Sonderman:
There is no need to submerge the chains in oil. The volts/cap
doesn´t exceed the rated limit and the ends of the string (full
voltage) are far enough apart, so there is no need for oil. They
don´t get warm at all (Gary´s get very slightly warm). The oil
wouldn´t cool them anyway, because of the plastic case
surrounding each cap (= insulator). Plus the fact, that they
are in open air, lets you check (or replace) them, if needed,
much easier and faster, compared to them being submerged
in oil. Oil is necessary for homebrew caps, but it is a pain, too.
This is one of the reasons why I went for the MMC deal. The
MMC is nothing else than a commercial pulse cap. PC
manufacturers do the exact same thing, we do with the MMC
(seriesing). The MMC has a secondary benefit that a
commercial pulse cap do not (at least not the ones used in
TC work) have: We parallel many strings. This means the total
current is divided up equally among the strings, which further
means the pulse current per cap string and per cap is low.
Big commercial (µF range) pulse caps use this trick, too.

Coiler greets from germany,
Reinhard