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Re: NST's in parallel

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.