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RE: Odd Variac Control And Transformer Really Buzzing ??


Greets,

> -----Original Message-----
> From: Tesla List [mailto:tesla-at-pupman-dot-com]
> Sent: Wednesday, March 08, 2000 12:30 AM
> To: tesla-at-pupman-dot-com
> Subject: Re: Odd Variac Control And Transformer Really Buzzing ??
>
>
> Original Poster: "Adam" <adamsmith-at-mediaone-dot-net>
>
> > 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).

The variac is a 10 amper, don't recall the VA rating I will
have to check tonight.  By the way it's not the variac that
is growling it's the NST.  It sounds like the 10 amp variac
will not be good enough for my Allanson 15kv-at-60ma.  I have
not fired the coil with this yet, I am building confidence
and knowledge from everyone here before trying it out.  Besides
the electricians wired all my 120 volt outlets, bathroom
hall bedroom garage lights onto one 15amp breaker. :-(
I have no idea how that could possibly have passed code.
I am going to have a 20amp breaker wired into the garage
hopefully soon.


>
> > 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).

This makes sense on all accounts.  I just tried out the Win Tesla,
and it states my cap should be 0.0088uF for that transformer.  My
MMC is 0.012uF.  I can drop a string on the MMC and get it to 0.008uf.
Will that be a close enough match to the transformer?

It looks like I will have to splice 4 more turns onto my primary.
I built the acrylic supports oddly enough to be able to add
turns later on just in cautious case, it just so happens to
have enough grooves for 4 more turns. :-) (LUCK)

I should have tried that WinTesla program out a long time
ago.  If my coil starts running better with the WinTesla
numbers I am going to have to send in my $20.  I'm sure
it will save me hundreds in trial and error in the near
term future. :-)

>
> > 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
>
>

Many Thanks,
Bill Parn