Re: [TCML] Power Factor Correction

[David Dean <deano@xxxxxxxxxxxxxxxx>]

Hi

On Tuesday 15 July 2008 12:40:47 pm Phillip Slawinski wrote:
> How do I know what direction to go with capacitance?  I'm running the NST
> with my Jacobs ladder to find the right value.

That will not give the correct value for a T.C.
There are two conditions encountered in a Jacobs Ladder. When it is arcing, 
and when it is not. When it is arcing, the output current is likely close to 
the short circuit current for the transformer. The correct PFC cap value for 
that condition will be close to the short circuit PFC cap value, which is 
what JavaTC gives you. When the arc breaks at the top, and before the next 
arc starts at the bottom, the correct PFC cap value will be very low, close 
to zero. During that period of time, if you have installed PFC capacitors 
close to the correct for short circuit condition value, the reactance of the 
PFC cap will be much lower than the reactance of the transformer, and most of 
the load as seen by the source will be the PFC cap. Most of the current 
flowing from the source during this period will be through the PFC cap, much 
greater than that which would flow through the transformer during the same 
period. 
 
> So far I've only found the 
> wrong value, and the very wrong value.  Turns out if you get it wrong you
> actually increase [dramatically] the amount of current being dumped into
> the NST.  I was running it and all the sudden the aspahlt I neglected to
> remove between the core and the HV windings bubbled up from the oil.  When
> I run without the PFC caps I'm drawing about 15A, with the caps I was
> pulling peak currents of 35A!  If I'm increasing current does that mean my
> capacitance is too high or too low?

Too high.

The way to find the best value of PFC capacitor for your Tesla Coil is to set 
up the coil with no PFC cap. Adjust for best operation, mark your controls so 
you can find that point again, measure the input current, and write down that 
value. Then add a SMALL PFC cap, say 20uF, return to the same settings, and 
measure the current again. IF the current is less than without PFC, then you 
can increase the PFC capacitance in small steps, repeating the process until 
you find the lowest (average) input current value. If adding a PFC cap of 
small value increases the average input current to the coil, then adding more 
capacitance will not help you any.

Hope this helps some,

deano


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