# Re: Capacitor calculation

• To: tesla-at-grendel.objinc-dot-com
• Subject: Re: Capacitor calculation
• From: "SROYS" <SROYS-at-radiology.ab.umd.edu>
• Date: Thu, 28 Sep 1995 10:06:08 EDT
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```> 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.