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Re: Small-ish polyprop. caps

Hi Sam,
	I am experimenting with smaller poly caps too.  I just got a batch today
and am wiring them together tonight (160  0.1uF 630V to give 0.01uF at
25000v).  Richard Hull and Bill Richards of TCBOR also experimented with
this many years ago, apparently with good results.  I don't think they used
polpropylene.  They put the caps stings in oil.  I am trying it in air at
first since it would be much easiler if it works.  There was a thread last
week about this.  Contact me if you missed it and I'll resend the posts to
you.  I am putting 10 Meg resistors across each cap to be sure stray or
unbalance voltages can't build up in individual caps over time and blow
them out.  I'll report what happens to my experiment soon.

	Terry

At 09:01 AM 11/5/98 +0200, you wrote:
>I'm a newcomer, working on my first coil, even. I'm curious about using
>these caps in a TC (which I seem to have a source for - not cheap, but good
>things never are...) They are BHC Aerovox (RBPS Series) polypropylene caps,
>designed to protect IGBT modules from large voltage transients. Besides being
>high voltage, they are rather higher capacitance than other dry pulse caps
>I've seen thus far, and also have rated dV/dt...
>
>So, the biggest ones are 3 uF at 1000V, 2 uF at 1250V and 1.5 uF at 1600V.
>They're rated at (dV/dt, in V/us) 400, 475, and 600, respectively, and at
>peak voltages of 1400, 1600, and 2100 VDC respectively. I did some simplistic
>calculations, I could just about use them at 200 kHz, 1000 V peak-to-peak and
>be just a bit over 600 V/us at zero-crossing point. (They're rated for a
>million pulses at 2 times rated dV/dt, 1000 pulses at 4 times, 100 at 6
times).
>So this means, if my math went right, that I'd need at least 12 of them in
>series to withstand operation with a 4 kV NST (my first setup), or perhaps
>even more with two 2 kV MOT's (my possible next setup). But how will it be
>in reality, the primary side I think doesn't have nice and clean sine-wave
>signals. How long will it work without blowing :-)
>
>