How to Test Variable Autotransformers?

[Bob]

I have a few variable autotransformers of unknown quality. What checks
and/or tests should be performed to ensure that they are (safely)
suitable for use? Can you recommend any URLs that I can study?


Thanks,

Bob

 

[James Sweet]

I have a few variable autotransformers of unknown quality. What checks
and/or tests should be performed to ensure that they are (safely)
suitable for use? Can you recommend any URLs that I can study?

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.

 

[Roby]

I have a few variable autotransformers of unknown quality. What checks
and/or tests should be performed to ensure that they are (safely)
suitable for use? Can you recommend any URLs that I can study?


Thanks,

Bob

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

 

[Bill Jeffrey]

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
==========================

 

[NSM]

I have a few variable autotransformers of unknown quality. What checks
and/or tests should be performed to ensure that they are (safely)
suitable for use? Can you recommend any URLs that I can study?

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

N

 

[Michael A. Terrell]

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

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.