Re: Capacitors

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

Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

At 12:44 PM 12/22/2000 -0700, you wrote:
>Hi Mike, Herein lies the question-what size cap do I need? I have tons of 
>information on computing
>cap size but for the life of me, I can't make sense of it. Any and all help 
>is truly appreciated.My
>transformer is a 15000volt nst with output of 450VA at 30MA. So far this is 
>all I know except that I
>won't make a plate stack cap. Later, Tim
>
>Tesla list wrote:
>

Hi Tim,

There are three common choices for cap size:

1.	The "resonant" size.  This is the value that will cancel the current
limiting of your transformer allowing a lot of power to be drawn.  It is
also the most risky and safety gaps are a big must.

For a 15/30 NST, that is 0.0053Uf or 5.3nF.

2.	The Larger Than Resonant (LTR) size.  At around 9-11nf  Well say 10nF.
This size is far safer and cause less strain on the parts but you still
have very good power.

3.	LTR for a rotary sync gap.  Since rotary gaps can precisely control when
the gap fires, we can play tricks (inductive kick effects) to pull more
power out of them.  That would be at 14nF for your NST.

I could babble on for hours about how these numbers are arrived at but I'll
spare you :-))

I assume you want #2 since you probably don't have a rotary gap for a first
time coil and I hate to recommend resonant caps to first time coilers since
that is how many blow their first NST =:O

I think you are contemplating an MMC so let's try MMCCalc3 with my 0.056uF
MMC caps.

==============================
MMC Calculator  Ver. 2.2   9/12/2000  Terry Fritz
Transformer voltage =  15000 
Transformer current =  .03 
Firing voltage =  21213.15 
Fo =  250000 
Break rate =  120 
Thermal dissipation constant =  40 
Individual cap value =  5.6E-08 
 
Strings  Caps/Str  Capacitance  Voltage   Temp C    Cost              I Arms
  2       11         10.18        17600     6.37   39.60  :-|   :-)   4.96 
  3       17          9.88        27200     2.67   91.80  :-))  :-))  4.82 
--------------------------------------------------------------------

The key number I use is the current which is about 5 amps.  Two stings will
do that (the program is a little conservative) so a 2 string by 11 cap MMC
would work.  You will note that even the "expensive" MMC caps here only add
up to $40 ;-))

Hope that give you an idea of how it all works.  MMCs are pretty new and
there are not any super well polished tools for figuring this stuff out
yet.  If you have any ideas about how to make this easier for a new coiler
I am all ears.

I am going to be bulk buying 0.056uF 1600V caps next month so stay tuned.
I am also working on a newer style MMC cap too but that is yet to be tested
but it is well directed for things like this.

Cheers,

	Terry