How to check a train transformer for safety

Last Updated on October 27, 2022 by Dave Farquhar

In spite of what a certain O gauge magazine tells you, vintage toy train transformers aren’t inherently unsafe to use. Age can take their toll on them, so you want to give them a good safety inspection, but as long as they pass the safety inspection, they can give you a long, productive service life. Here’s how to check a train transformer for safety.

All of my train transformers are at least 50 years old, and I expect my sons to inherit them in workable condition.

Use your senses

Start with a good visual inspection. If you see any rust, that’s a really bad sign. The presence of rust suggests the transformer was stored in poor conditions, and while rust on the outside doesn’t guarantee there’s corrosion on the inside, the two often go together. Likewise, a clean outside is a pretty good sign of a clean inside.

check a train transformer for safety
This Marx transformer had some rust on the underside, which wasn’t the best of signs. If the rest of it had also been rusty, I would have stopped right about here.

Pay extra-special attention to the power cord. If the power cord is in anything other than pristine condition, replace it. If the cord is frayed, broken, brittle, or missing, don’t mess around. It’s not worth risking your safety. I’ve also seen good cords with bad plugs. Fixing a plug is easy. If the prongs are bent, straighten them.

check a train transformer for safety
This is part of a bad power cord I found on a Marx transformer. Note the crumbling insulation and exposed wire. This cord is no longer safe, so I replaced it.

Don’t limit the inspection only to sight. Give it a sniff test too—literally. If the transformer smells like a burned up electric motor, don’t buy it. It’s done. The smell of a burned up motor is difficult to describe but impossible to forget. Basically, if the transformer smells bad, it is bad. If it doesn’t really smell like anything, it’s probably OK.

Before plugging it in

Believe it or not, you can give a transformer an electrical checkup without plugging it in. The key is to use a tool called a multimeter, switched to continuity tester mode. Multimeters have lots of uses in toy trains and model railroading.

Touch one wire of your multimeter to both of the prongs on your power cord. You can hold it in place with a little bit of tape if it makes it easier. Next, touch the other wire to any metal parts of the case. If you see continuity, stop. You have a major problem.

If the case checks out, it’s time to make sure there’s no measurable continuity to the posts. Proceed to the fixed voltage outputs. Then proceed to the common posts—marked “U” on most Lionel postwar transformers or “base post” on most American Flyer transformers. Finally, turn up the throttle and proceed to the other posts. Try the throttle in a few different positions.

Lack of continuity there doesn’t prove the transformer is going to work, but it gives some assurance the transformer isn’t a major safety hazard.

Plug it in

Here’s a safety precaution that’s easy to overlook: Plug the transformer into a power strip that has a circuit breaker on it. Why? If the circuit breakers trip when you plug the transformer in, you know right away it has a wiring fault inside that’s going to need the help of a professional, if it’s salvageable at all. If you can plug the power strip into a GFCI or, better yet, AFCI-protected outlet, even better.

But if there aren’t any initial issues, it’s time to test the operation of the transformer’s own internal circuit breaker. Do a bit of research to see if the transformer has one. Some of the least expensive transformers, especially Marx, don’t have one, but transformers of 75 watts and higher usually do. Marx and Flyer transformers that have breakers will have a button on the back to reset them.

If the transformer has a circuit breaker, test it. Turn on the throttle, then short the A and U posts (in the case of Lionel) or variable and base posts (in the case of Flyer) with a screwdriver or a piece of wire for a maximum of five seconds. The circuit breaker should trip with a click and the transformer should go dead. American Flyer transformers have a button to push to reset the breaker; Lionel transformers reset themselves after a short time. If the circuit breaker doesn’t work, the transformer needs professional help.

Finally, it’s time to check the outputs. Switch your multimeter to the lowest AC setting that it has. Don’t hook it up to the transformer in continuity mode while it’s plugged in—you’ll burn up the tool. Double-check to make sure it’s on AC, then test the fixed voltage outputs. It should read something close to what it says on the case, within a margin of error of about 10-15 percent. If your electrical outlets deliver 115 or 120 volts rather than the 110 volts that was standard in the postwar era, your transformer will probably deliver a little more too. That’s OK.

As long as the voltage of the fixed outputs is close, proceed to the variable outputs. Turn the throttle all the way up and measure the output. Flyer and Marx transformers should top out around 16 or 17 volts; a Lionel transformer may top out a little over 20 volts. Turn down the throttle and watch the voltage drop. It should drop as smoothly as the throttle moves.

If one of the variable outputs appears to be dead—a common malady on high-end Lionel transformers—there may be a quick and easy cure for that. Try connecting the other wire of your multimeter to a different U post. If it works, the transformer wiring is fine, you just have a broken post. That’s not a difficult repair, and there’s an easy workaround. In the meantime, you can proceed to use the other U post temporarily. It won’t hurt anything.

Final words

If the transformer passes all of these tests, it’s likely to be safe to use. Wiring in a circuit breaker, such as an American Flyer 1275 or Lionel 92, is an additional safety improvement.

I hope you’ll check out my entry on phasing transformers if you have more than one transformer and want to use them together. You might also like my tips for wiring a ZW or 1033 transformer.

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