Re: MMC Advice

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

Original poster: Robin Copini <rcopini-at-merlin-dot-net.au> 

Hi All,

  most of you would have seen my MMC cap using the CD942 series,

  I 'currently' :-) run a 33kv pt overdriven from 240v to 270v in at in
excess of 100amp
  and have never suffered a failure, heating, arcing or any other mishap with
the cap. The longest ever continuous run was over 8 minutes at FULL power.
The
Thoriated tungsten gap suffers more in my opinion! The system is inductively
ballasted
and runs very smoothly so long as the gap timing is correct.

Best Regards

  Robin Copini

  coil pics at www.geocities-dot-com/rcopini





----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, October 14, 2003 9:17 AM
Subject: Re: MMC Advice


 > Original poster: Mark Broker <mbroker-at-thegeekgroup-dot-org>
 >
 > I think I missed replying to this earlier.  Whoopsie! :)
 >
 > MOT coils with doubler/triplers are definately not something I have much
 > experience with, so others may be able to offer better advise.  I would
 > shoot for 16kV per string.
 >
 > A person has commented recently (on our forums) that they measured about
 > 300V across a PDT once with only 240 being applied (inductive ballast,
 > large primary cap)....  Events like that are one of several reasons why I
 > encourage "overdesigning" MMCs for non-NST coils.  NST coils have been
 > measured regularly and frequently and few anomalies have been reported wrt
 > overvoltage in a tuned TC.
 >
 > Dr. R recommends sizing the capacitor using 800V as the MMC voltage (2000
/
 > 2.5).  And for a coil that sees daily use for many years, I completely
 > agree!  But for a typical hobbyist who may put only a few hours of
 > operation on their MMC in its lifetime, I recommend using a voltage rating
 > closer to the maximum.  For PDT, PT, and MOT coils I suggest a maximum of
 > 1600V per cap.
 >
 > I would be most interested in comments from others on this matter!
 >
 > Cheers!
 >
 > Mark Broker
 > Chief Engineer, The Geek Group
 >
 >
 >
 > On Sun, 12 Oct 2003 22:19:33 -0600, Tesla list <tesla-at-pupman-dot-com> wrote:
 >
 > >Original poster: "Mudford, Chris" <chris.mudford-at-agresearch.co.nz> Hi
Mark
 > >
 > >I thought I was coming to grips with MMC's :-)
 > >
 > >I'm guesing you are meaning adding 25% more voltage in non-nst coils.
 > >So if one was to use a two series mot with voltage doubler (eg 2kv/mot,
 > >giving ~12kv pulsed DC) what sort of total voltage per string would you
 > >tend to recommend?  Or would you simply divide by the individual
 > >capacitor DC rating as long as there is a safety gap?
 > >
 > >Cheers, Chris (NZ).
 > >
 > >-----Original Message-----
 > >From: Tesla list [mailto:tesla-at-pupman-dot-com]
 > >Sent: Monday, 13 October 2003 4:07 p.m.
 > >To: tesla-at-pupman-dot-com
 > >Subject: Re: MMC Advice
 > >
 > >
 > >Original poster: Mark Broker <mbroker-at-thegeekgroup-dot-org>
 > >
 > >Fine....  if you really want to use RELL....  (see previous "CD cap MMC"
 > >post)
 > >
 > >Static gap, SRSG, ARSG?  Ballast type and value?  PSU output filter
 > >("Terry
 > >Filter")?
 > >
 > >I generally recommend adding about 25% or more to the margin in non-NST
 > >coils, and would argue that a cap rated for 16kV with a 11kV PDT is too
 > >low.  18kV would be minimum IMO.  Bigger caps, within reason, are
 > >generally
 > >better.
 > >
 > >Mark Broker
 > >Chief Engineer, The Geek Group
 >
 >
 >
 >