Re: Pig Question

["Gomez ADDams" <gomez-at-netherworld-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

on that fateful day 8/1/00 10:01 PM, Tesla list uttered:

> I was wondering if it is possible/nessecary to buy two trannies and wire
> them in series to produce 15,240 volts in order to reduce amperage and still
> keep the wattage the same.

You can run a large coil at 7.5kv, you just need to design it right.  OTOH,
for larger coils which prefer to have lots of joules/bang, it's a lot easier
to get more joules by increasing the voltage, since E=1/2CV!2
 
> Also when wiring the these transformers in series, do you just connect the
> ground (the case) together and draw the HV off each bushing?

If all you have is single-bushing transformers, that would be the only way
to do it, BUT: then one of the transformers will have its case floating at
7500 VAC!  Are you sure that's what you want?  Even if you isolated the case
on an insulating base, the low voltage bushings are not rated for 7.5kV, and
could well flash over to the 220V terminals.  That would be bad.

> And what is the 'up-to-date' current limiting method? arc welders and
> resistive ballast (oven elements)?

Most large coilers like a combination of adjustable inductive ballast and
resistive ballast.  Inductive ballast can be many things, but for something
adjustable, you probably want either a stick welder or large (39-50A) variac
with the core slotted to prevent saturation.  Unless you get lucky with
surplus, the latter option will prove prohibitively expensive.

 My gut instinct is that you want 2/3 to 3/4 of your ballast impedance to be
inductive, so as to waste the least power.  What has been the experience of
others in this regard?


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