ECN Forum Forums General Topics of the Trade General Discussion Area Transformer Problems

Hi,
I have a bit of a mystery. I have a step down transformer (120vac-24vac), that appears to be blowing the fuse on the high voltage side. It does this even when no load is on the 24v side. And it's not just one transformer, but 4 so far. The mystery is, there are three other transformers on the same circuit (within two feet of the problem) that are working fine. The electrician (I'm working on the equipment on the low voltage side) cannot find anything wrong, nor can I on our respective sides. Does anyone have any ideas or thoughts? Any information would be useful Thanks
Michael

Try putting it on its own circuit.

The inrush current of the transformers is probably the problem. Manufacturing tolerances may be the reason some of the units work and others don't.

Confirm the sizing procedure of the primary fuse, make sure you are using a time delay style. Sometimes a moderate to fully loaded transformer will have a lower inrush than a lightly loaded one.

Have you tried swapping the questionable transformer with one of the working ones?

The inrush current can be particularly high with toroidal transformers.

Sometimes you need to use a slow-blow fuse on the primary to give the necessary overcurrent protection but prevent blowing on switch-on.