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January 2017

Trainsformer Needed

I found a bargain at a local thrift store and now have a 1959 Marklin HO Scale train, cars, and track. The set didn’t come with a transformer, so I thought it would be a fun project to build from scratch. Does anyone have a schematic or suggestion for a DIY train transformer they can share?

#1172
Alfred Thompson
Kingsport, TN



Answers

I have been collecting Marklin trains since 1962. I believe, what you are looking for is the 16-20VAC transformer Marklin used to require. The basic power pack was a variable voltave, 0-16VAC approximately, transformer. It had a lever to rotate which increased/decreased the voltage output.

To reverse the engine, the hadle was pushed down momentarily, which would send 20VAC to the engine, which toggled a latching relay in the engine to reverse the ‘brushed, AC motor.’ Were I, and I might in the future, to design a solid state replacement, I would select a PIC24F or PIC33F series processor and have it geneterate a PWM sign wave. There are app notes at the Microchip website specifically regarding the digital generation of sine waves. Then you can vary the frequency for speed control, rather than the voltage, which would give much better low speed response for the engine.

Mark Lampkin
Grand Rapids, MI

Boy are you lucky!!! I started collecting Marklin HO scale back in 1962, so a 1959 vintage should be fabulous.

The old equipment had AC motors in them, and the original transformers ran 16VAC to 20VAC. In other words, they were variacs which controlled the speed by changing the voltage to the tracks. This did pretty well, except at the very lowest speeds.

So, there are a number of ways to control the locomotive. The easiest would be to use a transformer output through a potentiometer, driving a 30 or 40 watt amplifier, (direct coupled). This output would directly couple to the track. The center spikes are the Hot, with the rails being the neutral.

A more complicated, (but fun way depending on your skill level), would be to use a PIC microprocessor to PWM a sine wave to directly drive the center rail of the track. Then you would have the most control.

Mark Lampkin
Grand Rapids, MI

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