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Re: Neon Transformers With/Without PFC

> Someone mentioned recently that 15kv neons were not that rugged or suited to
> Tesla coil work.  I was just wondering if there is some consensus on a good
> value to use, or if any one manufacturer is better than others.

On the contrary, they work quite well in Tesla coil work.  They are internally 
current limited as opposed to most transformers where you would have to use
some sort of inductive\resistive ballast in series on the low side to control
the current.  They are are definitely not as rugged as power distribution 
xformers but will hold up to the job if an overvoltage safety gap is used 
across the high side and filtering is used to keep large amounts of RF from
circulating through its windings.  This is definitely the way to go for
coils up to a few KVA or for somebody just starting in this hobby.  With
the internal current limiting you just hook it up and go.
 
> Also regarding power factor correction:  Is the 90 degree phase difference
> between the voltage and current in a purely inductive load what causes the
> power loss?  If so, then is the capacitor value determined by finding the neon
> primary's impedance and matching it in Farads?  Is such correction needed on
> other types of transformers like pole pigs?  

To the first question, yes.  Since you have resistance and inductance in a circuit
though the two combine to give a a phase angle anywhere from 0-90 degrees.
The cosine of this phase angle is the power factor with a power factor of
one being unity or perfect power factor. 

The apparent power is the power you put into a circuit measured in volt-amperes
(VA).  The power consumed by the resistive load is true power and is measured
in watts.  The power circulating in the circuit due to reactance is measured
in volt-amperes reactive (VAR).  The power factor of a circuit is found by
dividing the watts consumed by the volt-amperes you are putting into the circuit.
If you are putting in twice as much power as is actually being consumed by
the load you have a .5 power factor, which is pretty poor.  If you are putting
in the same power as is being consumed you have a power factor of 1.

You need to find the the inductive reactance of the transformer and match that
that with the same amount of capacitive reactance at 60 hz.
The inductive reactance is 2 x PI x frequency in hz x inductance in henrys.
The capacitive reactance is 1 / (2 x PI x frequency in hz x capacitance in farads).
You want the reactances to be equal at the operating frequency.  

You only need to use power factor correction if you are being limited by the 
amount of current you can supply to the transformers.  Lets say your neons are
supplying 2400 VA to the coil.  If you're running 120 volts in at a perfect power
factor that is 20 amps. Without PF correction lets say you draw 25 amps. That's
really no big deal, you are still delivering 2400 VA to the coil, you're just 
feeding the xformer with an extra 5 amps to feed the reactance.  Again this is 
not power that is consumed so you are not paying for it.  You only pay
for watts consumed.  Where all this could come into play is if you are trying
to feed the above circuit through a 20 amp variac or you are running all this
on a 20 amp house circuit, you would want to keep the current as low as you
could.  For the most part PF correction isn't worth the trouble until you
reach a point where you want more power but your LV equipment just can't
provide it.

> Please forgive me if these questions seem too obvious.  I recently dug out an
> old electronics textbook and have been trying to bone up on some basics...it's
> been a while.
> 
> Charles Brush
> 

No problem, I hope I've helped.   -Mike McCarty