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On 9/18/18 10:52 AM, jerry miller wrote:
That is interesting I've been trying to find out if you can feed a pole pig
with a 60 Hertz d/c Square wave with adjustable duty cycle or in other
words a pwm. Which would think that it would work for current limiting
or??
I think someone on the list fooled with using a Variable Speed Motor
Drive (aka VFD) (which generates a pseudo sine wave at a commanded
frequency and voltage) to feed a HV transformer.
I don't know that I'd feed a square wave, when it's so easy to get a
reasonably sinusoidal waveform these days.
Or, if you're looking at doing current limiting? About 20 years ago, I
experimented with using a FET chopper to be a "solid state variac" - in
my case I was driving a single phase AC capacitor run motor. It kind of
worked ok, but was kind of complex to make it work, and when decent
single phase VFDs became cheap it wasn't worth it.
But you might be to make a PWM current limiter (a pseudo ballast).
If you're talking about feeding a pole pig with different frequencies, I
think that would work - your losses would go up as the frequency goes up
(the lamination thickness is chosen according to skin depth at the
operating frequency... thinner laminations are more expensive), but that
might not be a big problem in tesla coil duty.
We do testing at work using a pair of solid state 600W Crown PA
amplifiers driven by a lab oscillator. It can put out 120V without any
problem. A similar sort of thing is done to drive a vibration testing
table.