Using old transformers with new

Last Updated on April 15, 2017 by Dave Farquhar

I’ve covered phasing transformers before, which allows you to use more than one transformer on a layout. But I read something today that reminded me of an old question: Can you safely use a modern Lionel transformer, such as a CW-80 or new ZW, with postwar transformers?

Unfortunately, changes between new and old make it difficult. You can use one to power trains and one to power accessories, but you shouldn’t mix them on the same loop of track. Read on to see why.

Note that modern transformers from companies like Model Rectifier Corporation (MRC) and MTH operate in the same fashion as vintage Lionel. What I’m going to say from here on regarding modern transformers doesn’t apply to them. For the sake of this discussion, regard those transformers as equivalent to vintage.

Vintage Lionel transformers output true sine wave alternating current. Modern Lionel “transformers” would really be more accurately described as power supplies than transformers. They output a chopped wave. This causes problems with some other makes of trains, but it also causes a problem if you have a track block powered by a modern transformer and an adjacent block powered by a vintage one.

When the train crosses that block, the two transformers get connected in parallel for the brief moment that the train crosses the block. If the two transformers are properly phased and they’re set to the same voltage, that isn’t a problem. But if one transformer is outputting a sine wave and one is outputting a chopped wave, they aren’t truly phased, so for an instant, the train receives double voltage.

On a traditional layout with no command control, where you’re likely to run at 8-10 volts, that’s not a huge problem. The train gets a very brief burst of 18 or 20 volts. That’s the upper limit of what the train is designed to handle, but you’re still within the bounds of reason.

If you’re running command control, though, you have your throttles set to 18 volts. So when your train crosses that bridge, it will be getting 36 volts. And the wiring in your train (and your vintage transformer) isn’t designed to handle that. It won’t break the first time you do it or necessarily even the 12th time, but eventually, you run the risk of burning up a wire in the locomotive or the vintage transformer.

So don’t do it.

If you have separate tracks that never cross, you can safely use a vintage transformer on one and a modern one on the other, and you can phase them to reduce the number of wires you have to run all over the place. And you can safely use one type of transformer to run trains and one type of transformer to run lights and accessories and the like.

But if you run command control, or plan to ever run command control, mixing the two for running trains isn’t worth it.

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