How to Test Variable Autotransformers?

Suitable for use with what? A visual inspection and connecting one to power and measuring the output is about all I've ever done to check them, they're pretty simple devices, not much to go wrong really.

I have seen autotransformers designed for 400 Hz on the surplus market. They will draw excessive no-load current if powered up at 60 Hz ... unless you derate the input voltage by 60/400 = 0.15, which makes them rather useless.

Hopefully, yours have nameplates indicating ratings.

Roby

If you can visually inspect the windings, that's a good thing to do. I have run across a couple in which one or two of the turns developed some slack - who knows how? The slider tends to catch on the slack turn, which will probably make some fine fireworks if it drags the loop or breaks it.

Bill Jeffrey ==========================

James Sweet wrote:

Slap a load on them. Add a regular light bulb. Otherwise check ground and insulation.

That's easy enough to test for. Put a 150 watt lamp in series with the primary and power it up with no load. If the lamp lights brightly the transformer is either bad or built for a higher line frequency.