Re: MMC Advice

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

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