I am replacing a faulty 110-to-220V AC transformer:

Chinese Transformer

The new transformer is a Bel Signal A41-130-230. It has a little higher VA rating (130 instead of 80) and also features dual primary and secondary windings:

New Transformer Wiring

I have connected pins 1 and 5 to line and 2 and 6 to neutral on the primary winding (taps in parallel). I've bridged pins 8 and 11 on the secondary winding (taps in series). I measure 126.4 V AC on my line voltage. Based on the specifications of this transformer, I would expect 2X the voltage on the output, or 252.8 V AC. I am measuring 272.6 V AC across pins 7 and 12, which is about 7% higher than expected. This is open-circuit voltage (no load).

The components in this equipment are rated for 220-240V. Have I selected an improper replacement transformer, or is the voltage merely higher because it is not connected to a load?


2 Answers 2


Transformer output voltages are rated at a given load. The specs for the 130VA transformer says 230 VAC at 0.57A load. As you can see the transformer with lower 80 VA rating has 230VAC at 0.35A.

Open circuit voltage under no load condition will be higher than the voltage at rated load condition.


It will decrease once you load it down so it needs to output current. If you want to tow something at 60km/h, you don't pick a truck that has a top speed of 60km/h dragging nothing. You pick something that can go faster because it slows down when dragging something.


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