Electronic – Reasonable maximum exciting current 60Hz step up transformer


What should be a resonable exciting current for a 720VA 60Hz transformer? Primary 12V/60A and secondary 110V. I'm measuring about 2A (around 3% of maximum rated current) in the primary while the transformer is idle (secondary open circuit). This is the step up transformer of my inverter project.

Another question: when the transfomer is fully loaded @ 720VA, suppose for simplification a pure resistive load, does this exciting current still represent a loss? I.e, are these 2A still wasted? I understand part of this current is just reactive and part is effectivelly loss. I'm trying to figure out the maximum theoretical efficiency of a system like this.

Best Answer

Your measured 2 A open-circuit current seems reasonable. You are measuring 24 VA, but the watts loss may be about 1/3 of that or 8 watts. You can assume that will be the iron loss and that it will not change with load. Once you load the transformer, you will see copper loss added to that. If you want to determine the efficiency of the transformer, you will need a wattmeter. If you search the internet, you should be able to find the procedure for performing open-circuit and short-circuit transformer tests and calculating copper losses.