Re: MMC voltage ratings

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jason Petrou by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jasonp-at-btinternet-dot-com>

Marc,

Surely a resonant or STR cap would be much better for a static gap - this
allows the gap to fire more reliably because of a higher voltage across it.
With an LTR cap the you dont get such a high firing voltage, particularly if
the cap is very LTR.

Best Regards,
Jason
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, November 27, 2001 3:55 AM
Subject: Re: MMC voltage ratings


> Original poster: "Mark Broker by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<mbroker-at-thegeekgroup-dot-org>
>
> Jonathan,
>
> 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.....
>
> Mark Broker
> 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>
> >
> >Hi Johanthan,
> >
> >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:
> >
> >http://hot-streamer-dot-com/temp/MMCcapSales.gif
> >
> >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:
> >
> >http://hot-streamer-dot-com/TeslaCoils/MMCInfo/GeekCaps/GeekCaps.htm
> >
> >I can't speak to the JAVA MMC calculator but is should work.  I can't
find
> >the URL or I would try it.
> >
> >Cheers,
> >
> > Terry
> >
> >
> >At 08:47 AM 11/20/2001 -0800, you wrote:
> >>Hi All,
> >>
> >>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.
> >>
> >>Jonathan Peakall
>
>
>