Re: triacs

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jan Florian Wagner by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jwagner-at-cc.hut.fi>

Hi,

> 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.

A variac can be thought of as an inductive voltage divider, exactly the
same way like a potentiometer. 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". 
See:
http://www.st-dot-com/stonline/books/pdf/docs/3566.pdf

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

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