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Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>" <davep-at-quik-dot-com>
Tesla list wrote:
> Original poster: "Jan Florian Wagner by way of Terry Fritz
> > A fellow at uni gave me half a dozen 30 A triacs for free today. Is
> > there anyway I can use these in parallel or whatever to replace a
> > variac? I have never seen anyone use a triac for voltage regulation for
> > a tesla coil before.
cf any of the archived discussions of light dimmers.
> A variac can be thought of as an inductive voltage divider, exactly the
> same way like a potentiometer.
I wouldn't think of it that way. There is some similarity,
many differences. The the losses inherent in a potentiometer
are essentially absent, improving efficiency and cooling
problem. The variac is a tapped, variable transformer, so
power in is roughly power out, the voltage reduction being
accompanied by a current increase, via the mag flux in the core.
> The output tap gives you some fraction of the input voltage, i.e. you
> can smoothly control the output voltage.
> With triacs you can only control the output power (for the case of AC
> output, which you need to drive the HV transformer prmary), which is done
> by "chopping up the mains voltage into small bits".
> Triacs work just nice nowadays even with inductive loads like
> transformers (NST, MOT, whatever, dunno about pole-pigs though ;o), but I
> think those 30A ones might be rather low-voltage ones and not suitable for
> 2..3*mains voltage(?).
> - Jan