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Re: Capacitor calculations

> 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%.


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