# Re: Capacitor calculations

• To: tesla-at-grendel.objinc-dot-com
• Subject: Re: Capacitor calculations
• Date: Tue, 26 Sep 1995 10:41:16 EDT
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```> I have seen several postings recently regarding calculating the
> correct capacitor size for a given transformer.  I assume these values
> are coming from a program such as TESLADP.  I tried this for my pole
> pig and get a value of .064 mfd.  What does this mean?  I would
> guess that this is the maximum value this power supply can charge
> effectively in a tesla tank circuit?

I'm not familiar with the Tesla programs either , but I have seen
capacitor selection described as a problem in impedence matching (i.e.
-  for the most energy transfered, the impedence of the load should
match the impedence of the source).

In English, for a transformer with a given voltage (=V) and current (=I)
rating, you first calculate the impedence that will load the transformer to
it's rated capacity (R=V/I).  For the maximum output from a transformer,
the capacitor you choose should have a capacitive reactance (=Xc)
equal to the transformer's impedence (=R) at your line frequency (f =
60Hz here in the good old USA, 50Hz elsewhere).  The capacitive
reactance can be found using Xc = 1/(2 * pi * f * C)  where C =
capacitance in Farads.  From the desired Xc that you computed, it's
simple to find C = 1/(2*pi*f*Xc) to fully load your transformer.  Since this
formula is for the steady state condition and a capacitive discharge
Tesla coil is not running at steady-state, the value of the capacitor
found above can be increased by 50% to 100%.