Re: variac size and flashover

In a message dated 11/12/99 5:07:50 AM Pacific Standard Time, 
tesla-at-pupman-dot-com writes:

> Original Poster: pmathus-at-learningco-dot-com 
>       2 questions for the gurus:
>       1)  How big a variac do i need? 5 amps?  15 amps? I'm going to be 
>       running a 12kv 60ma NST.
>       2) What's the recommended distance between the first turn of the 
>       primary and the secondary to prevent flashover?  I was thinking 2", 
>       (for a 6" secondary) but now i'm wondering if that's too much. . .
>       thanks,
>       paul mathus

I would use a 10 amp variac.  This will work fine without needing any pfc 
correction caps on the primary of the transformer.  If you later add another 
transformer, you can add pfc caps to reduce the current draw and probably 
still get by with a 10 amp variac.  If you add another 30 ma transformer in 
parallel and use pfc caps, you should be just barely over 10 amps.  You can 
normally draw over the rated current by 20 or so percent since it won't be a 
continuous duty situation, so you could probably controll two 60 ma 
transformers in parallel.  This hobby has a real tendency to get out of 
control.  Once you get the coil properly tuned and running well, you will 
immediately start thinking about adding more primary capacitance and more 
primary power.  With this in mind, get the largest variac you can find and 
still afford.

2" primary to secondary clearance should be fine.  That is what I use on my 
6" coil.

Ed Sonderman