Re: MMC cap bank

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

Original poster: "Shane Rusch by way of Terry Fritz <teslalist-at-qwest-dot-net>" <str-at-itol-dot-com>


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Thursday, July 03, 2003 8:53 AM
Subject: RE: MMC cap bank


 > Original poster: "Lau, Gary by way of Terry Fritz <teslalist-at-qwest-dot-net>"
<gary.lau-at-hp-dot-com>
 >
 > I'm not sure I agree with this dismal assessment.  MMC caps are typically
 > designed with voltage ratings governed by the cap's DC rating, not the AC
 > rating.  The proposed cap's string rating was 25kV, a reasonable margin
 > above the peak voltage from a 14.4kV power supply.  The difference between
 > a pig and an NST application is the RMS current.  An MMC designed for a
pig
 > must handle higher current, so more parallel strings must be
 > used.  Designing longer strings won't improve the ability to handle higher
 > currents.  Longer strings of the same cap size will result in lower
 > capacitance per string, so more strings will be required to achieve the
 > desired final capacitance, but it would be more economical to just use
 > shorter strings of smaller caps.
 >
 > That said, I don't know if the proposed BC caps have a proven suitability
 > for MMC's.  The price does seem attractive though!  I think Terry
commented
 > that they appear somewhat small compared to other similarly rated units?
 >
 > Gary Lau
 > MA, USA
 >
 >  >Original poster: "Dr. Resonance by way of Terry Fritz
 > <teslalist-at-qwest-dot-net>" <resonance-at-jvlnet-dot-com>
 >  >
 >  >The rating you specified alone should tell you it won't work for a long
 >  >time --- perhaps short time until you start blowing them.
 >  >
 >  >The pig is 14.4 kV and you intend to run the cap string at 900V x 10
which
 >  >only equals 9 kV.  Failure is certain --- the only question is when.
 >  >
 >  >With NST's we use 13-14 caps per series.  With pole xmfrs I would
recommend
 >  >around 16 caps per series as an absolute min.
 >  >
 >  >Less than this will eventually begin to failure.
 >
 >
 >  >> Hello all,  I'm constructing my first mmc bank. Cap's are .056 uf.
each,
 >  >> 2500 vdc. 900 vac. each. 10 per string .0056 total per string, a total
of
 >  >> 10 strings max. .056 possible, probably tap out a smaller value at
first
 >  >> although. Cap's are digi-key # BC2048-ND, AC and pulse double
metallized
 >  >> polypropylene film. Bleeders are 10 megohm 1/2 watt. Using 14.4 kv. 10
kva.
 >  >> pig, MOT. ballast on primary, asynchronous gap, speed is ajustable so
it
 >  >> may be in synch. at some point. Will it last?  Comments? Thanks
Arcing
 >  >> in Wisconsin.......
 >

Thank's for the comment's I guess another thing to consider is the voltage
drop when using MOT ballasting. The formula I used to calculate the cap's is
located at http://users.better-dot-org/tfritz/site/MMCinfo/MMCPower4.html  it
comes up to 282 hrs. I'll try them out and let you know how they last......
Arcing in Wisconsin

http://hot-streamer-dot-com/TeslaCoils/MMCInfo/MMCPower4.html

 >
 >