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Tesla, PFC


 RE> I haven't played with PFC's before and have a question for you.
 RE> Right now I have a little coil that uses a 10kv/23ma ignition 
 RE> xformer. Do you think it would improve performance (such as it is) 
 RE> to add a PFC cap ? If so, whats your best guess for the value? 
 
OK, for those not up on the subject "PFC" stands for "Power Factor 
Correction". PFC capacitors are placed across the primary winding of
internally current limited (or internally shunted) step up xfmrs to
decrease the rms current draw, and thus increase the transformer
efficiency. Typically we are talking about neon sign and oil burner 
ignition transformers. PFC capacitance added to these transformers 
does not affect the power output.

PFC capacitors really come into play on large HV power supplies that
consist of several neon sign transformers wired together to form a 
"bank". It is not at all unusual for banks of neons to trip a common 
household 30 amp breaker (or blow 30 amp fuses) at 120 volts; even 
though the output from the banked power supply is only 1.5 kVA 
(kVA = kilo*Volt*Amps = ~kilowatts). By adding power factor capaci-
tance across the step-up primary it is possible to reduce the amperage
draw by nearly 50%, resulting in a considerable reduction of stress to
the supply circuit. This also reduces the size and cost of a variac 
used for voltage control of the step-up power supply.

I would not go out of my way to power factor correct an oil burner 
ignition transformer with only a 230 VA output.

 RE> Not being up on PFC theory, would a value less than the calculated 
 RE> one have any effect ?

Yes.

 RE> I have a 13.5uf/330vac I pulled from something I was thinking about
 RE> throwing across my transformer. I read your posts on PFC, but all your
 RE> references were for neon xfr's.(thanks for the cool posts, though.)
 RE> Thanks in advance...

Go ahead and experiment. Hook up an ammeter, run the coil, and measure 
the draw from the line. Then put the cap across the line as close to the
transformer primary winding as possible. Re-measure the line draw with 
the coil running. You should see a reduction in the current draw.

Richard Quick



... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12