Re: NST's in parallel

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Original poster: Ed Phillips <evp@xxxxxxxxxxx>

Original poster: "Drake Schutt" <drake89@xxxxxxxxx>

Hello all,

I am a bit curious about wiring neon sign transformers in 
parallel.  All i know is that you connect the cases together and 
connect the positive and negative leads together (there's probably 
more to it than that).
Also it has been said that it is best if the NSTs are the same 
voltage, amperage, brand name, etc.  Is it possible to wire up some 
NSTs in parallel with different voltage and amperage ratings?  If so 
how would you calculate the total wattage?  What about the same 
voltage/amperage transformers but different brands?

any response is appreciated as always,
Drake "

   Certainly it works - I've used a 12 kV and 15 kV 60 
ma  transformer in parallel and no problems at all.  To figure out 
what you're going to get with a resistive load you need to know the 
voltage and leakage reactance of each transformer.  You can then draw 
the parallel equivalent circuit with various voltages and reactances 
and calculate the total current deliverd at any terminal voltage LESS 
than that of the lowest transformer.  Any transformers whose 
open-circuit voltage is lower than the operating voltage will 
actually have current flowing into them, which of course doesn't 
help.  An equivalent method is to pick a hypothetical output voltage, 
consider each transformer by itself and calculate the current 
flowing, then add up the results.

    Things get a bit more complicate if you're feeding a capacitive 
load of course.

   I suspect the difference in brands is relatively small but have 
no data to back it up as all the transformers I have are Franceformers.

Ed