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Ammeter readings with MOT power supply



Original poster: "Breneman, Chris" <brenemanc@xxxxxxxxxxxxxx>

Hello,

I've almost finished the MOT power supply for my first Tesla coil, but have a few questions about its operation. The supply consists of two MOTs with the primaries in parallel and secondaries in series and a third MOT in series with the parallel arrangement of the first two acting as a ballast. The ballast has its high voltage winding shorted. All of them run on 120V. In addition to the transformers, I also have a 15A circuit breaker in series with the circuit, and the house has its own 15A breaker on this circuit. I recently received a 15A analog panel ammeter which I wanted to use in the circuit to monitor current drawn. It is placed in series between the breaker and the ballast. When I run the power supply with the hv end shorted, no breakers trip, but the ammeter reads off the scale. When I replaced the analog meter with a digital multimeter capable of reading up to 20A, it read "Overload". What I don't know if if more than 15A is really flowing, and if it is, why it isn't tripping the breakers, and if it isn't, why do the meters show that it is? The only possible cause I can think of for this discrepancy is that the power factor is probably greatly offset by the highly inductive load, but why wouldn't the breakers trip in this case? I also tried the circuit with a 10uF PFC capacitor, and saw no difference in behavior. If the problem is the power factor, do you think a 180uF PFC capacitor would be reasonable for such a supply? The open circuit voltage is slightly over 5kV and the short circuit current is slightly over 500mA (that is, assuming these readings from the digital multimeter are correct; I determined these values indirectly by measuring current through different resistances on the hv side).

Thanks a lot,
Chris