Re: Capacitor calculation

> TE>In English, for a transformer with a given voltage (=V) and current 
> TE>(=I)rating, you first calculate the impedence that will load the 
> TE>transformer to

> ...

> A pole pig (or microwave transformer) is designed to not current
> limit at small values so the capacitor maybe as large as you like
> (within reason) and the capacitor voltage will follow the
> transformer output voltage, but the current will be initially
> very high and fall off as the voltage reaches it's maximum at the
> quarter cycle. You arrange the gaps to fire just at the top of
> the quarter cycle (maximum voltage) and transfer the stored
> energy in the capacitor through to the primary in a very short
> time, thus getting a good pulse of current.

Physics is physics.  There is nothing magic about a Tesla coil so 
unless something else is going on with a pole transformer compared to 
a neon sign transformer, the capacitor selection should hold regardless 
of whether you're using a 200 VA oil burner ignition transformer or a 
50kVA distribution transformer.  That's not to say that you couldn't put a 
larger or smaller cap in the cicrcuit and have it work, but a basic theory 
in EE says that to get the most power (=I^2 * R) in the load, the load 
impendence should match that of the source.  Again, since a Tesla coil 
is not running in a steady-state condition, this calculation will give you 
a ballpark figure as to what capacitance you should use rather than a 
definite "Use this or else" value, but it should work regardless of your 
supply.  BTW - for what it's worth, I have heard/read this description 
and associated calculation from both Duane Bylund and Richard Hull 
and neither one restricts it's use to a particular type of transformer.

Steven Roys (sroys-at-radiology.ab.umd.edu)