Re: 10amp Hump

From: 	Bert Hickman[SMTP:bert.hickman-at-aquila-dot-com]
Sent: 	Sunday, June 22, 1997 7:34 PM
To: 	Tesla List
Subject: 	Re: 10amp Hump

Tesla List wrote:
> From:   George W. Ensley[SMTP:erc-at-coastalnet-dot-com]
> Sent:   Friday, June 20, 1997 12:40 PM
> To:     tesla-at-pupman-dot-com
> Subject:        10amp Hump
> All,
> I got my new 5KVA pig from T&R this week. EXCELLENT SERVICE!
> Ordered it on Friday got it on Wednesday. Boy is it big 250 lbs and almost
> as tall as my wife.
> Only having a 110v variac i am driving 1/2 the pigs primary. The welder is in
> series, with a couple of 1500w heater elements across the welders  primary.
> What is interesting is that i see a 10amp hump in current as i bring the voltage
> up before the gaps fire, no load. The hump is reduced by the heaters and
> when the gaps fire the current goes up as expected but seems excessive for
> the results produced by the TC. Any suggestions?
> George.......


Sounds like you're seeing 60 Hz resonance between the leakage inductance
of your pig, the series inductance of your welder, and your tank
capacitor. The reduction you're seeing with the added resistive ballast
is because you're reducing the "Q" of this circuit by adding the
resistor elements. The series LC combination of the transformer and
welder inductance and your tank capacitance (that's reflected back into
your primary as a much larger value) results in significant resonant
voltage rise in your pig's secondary side, and a significant increase in
primary current draw even with the gap not firing. Changing the value of
the series inductance may take you out of the sensitive range, and
addind resistive alelments will also keep the Q down, reducing this
effect as you've noted. To prevent potential damage to your tank caps,
you should probably add a safety gap across the secondary of your pig,
before the RFC's to your gap and tank circuit. 

-- Bert --