[Prev][Next][Index][Thread]
Re: Odd Variac Control And Transformer Really Buzzing ??
> Original Poster: "William Parn" <parn-at-fgm-dot-com>
>
> Transformer is 9kv-at-30ma NST.
> If my spark gap does not fire right away when I hit
> the power to the Variac then the NST starts groaning
> really loud. Turning up the Variac does not get the
> gap firing it just makes the NST groan more.
What is the VA rating of the variac? Usually when they buzz, they've got
LOTS of current going through them, as in more than they like. Maybe you
need a large variac. A 10 amper should suffice for this, but get an 18 to
25 amp one if you can, since you'll likely want to move to a larger
transformer soon (explained more below).
> If I turn the variac off and wait a couple of seconds
> and pop the power to it. The gap starts firing and
> streamers a flowing.
>
> Does someone know why this is. I thought one of the
> points of the variac is to bring the power up slowly,
> I don't understand why it is not working that way.
Your main gap is too wide, or your transformer supply is not putting out
enough current to charge your main cap in the required amount of time (i.e.
you have an ABTMLTR cap (a-bit-too-much-larger-than-resonant). Probably
both.
The reason you get performance when you flick on the power really fast, is
the initial over-volt spike from the NST which starts the gap firing. One
the gap is going, ions hanging out in there can lower its effective distance
(i.e. it's breakdown voltage on subsequent bangs).
> When I run with diodes I don't see this behavior, I can
> turn the variac up and down, starting and stopping the
> firing of the gap.
That's because the cap is charging to the same polarity on both halves of
the AC cycle, until it reaches the gap breakdown voltage. This again points
to your cap being to large for your transformer.
-Adam
adamsmith-at-mediaone-dot-net