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Re: MMC voltage ratings
Original poster: "Mark Broker by way of Terry Fritz <twftesla-at-qwest-dot-net>" <mbroker-at-thegeekgroup-dot-org>
In general, an LTR cap will work as good as or better than a resonant or
STR cap with a properly set main gap. In other words, if you add more
primary capacitance and
retune without touching the gap spacing/timing, you *should* get
approximately equal (or even a little bigger) sparks when compared to a
resonant cap. In addition, a
resonant setup will put more of a voltage stress on your cap and
transformer. We (The Geek Group) do not generally recommend a resonant
-sized cap, and really only
included that column in the chart for reference purposes. In addition, we
offer BIG caps, which make smaller MMCs unresonably large (needing 29 caps
in series for a 15/30,
if memory is correct!)....
According to C-D, the Geek Caps (C-D P/N: 942C20P15K) can handle 13.5A RMS,
432A peak, with a dV/dt of 2879 V/uS (5mohm ESR, 32nH ESL).... But, I
think Terry's tests
(link below) is far more indicative of "Tesla-Duty" conditions than C-D. I
forget the frequency they test their caps at....
Sorry for the delayed reply - was enjoying my vacation, and found about 450
emails this evening after work.....
The Geek Group's Chief Engineer.
11-20-2001 12:46:50 PM, "Tesla list" <tesla-at-pupman-dot-com> wrote:
>Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
>A 15kV transformer has a peak voltage of 21kV. 10 2000 volt caps give 20kV
>which is close enough since MMC caps can easily be pushed somewhat beyond
>their ratings without worry.
>As Mark's chart at:
>Shows, 2 strings are fine. The current is about 12 amps which is just at
>what they can take without worry. More info is at:
>I can't speak to the JAVA MMC calculator but is should work. I can't find
>the URL or I would try it.
>At 08:47 AM 11/20/2001 -0800, you wrote:
>>I am making my MMC, and am a little unsure of whether I have an adequate
>>voltage rating. The Geek site says this is ok, and the Java MMC calculator
>>says the reliability is bad. I must be doing something wrong, as it says all
>>my designs are bad, even when I put silly numbers of caps in a string. Could
>>y'all weigh in on this one? I want to make a good one that lasts. My specs:
>>PSU: 15/120, static gap, desired tank cap around .03uf (LTR)
>>I have 22 caps, .15uf/2000VDC. The Geek site says 2 strings of 10 will be
>>ok, this would be .03uf/20kv. Does this have an adequate safety margin?
>>I could go closer to resonant and get 8 more
>>caps, and have 2 strings of 15 for .02uf/30kv. Is .02 close enough to .0212
>>(the value listed as resonant) to be resonant?
>>Once again, as always, thanks much.