3 rail question.... help ! | O Gauge Railroading On Line Forum

Davy MacOGR Forum Member

Hi Guys,

I have an old Williams 4-6-2 (cat no 4949) which is 3 rail. I'm not into three rail and intend to convert the loco to 2 rail ,however can anybody tell me why the loco only goes in one direction (forward) no matter if I swap polarity

to the motor terminals ? In 2 rail operation swapping polarity would make the loco reverse but I don't get this 3 rail malarkey . Can anybody explain ??? I'm a blind man in the dark with this ??? Cheers DAVY

4/1/125:54 PM

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ADCX RobOGR Forum Member SUPPORTING MEMBERDIGITAL SUBSCRIBER

As the motor is a permanent magnet field DC motor, there is a bridge rectifier on board that runs the loco forward whether connected to AC, DC- or DC+.

4/1/125:59 PM

Jim PolicastroOGR Forum Member SUPPORTING MEMBER

Davy,

Some of those early Williams engines had no reverse unit. They were equipped with a rectifier, as Rob said, so that they could operate on AC but only in forward.

If you remove the rectifier and wire the motor leads directly to track current, it will then reverse direction with DC polarity changes. Of course, it will no longer operate at all on AC if the rectifier is removed.

Jim

4/1/126:02 PM

Arthur P. BloomOGR Forum Member

"I don't get this 3 rail malarkey"

Actually, it's not Malarkey, it's physics.

As others have said, here is the easiest way to understand it:

What you have: Toy Track----->AC----->rectifier----->DC------>motor

What you need: Scale Track----->DC----->motor

See? simple. Just disconnect the input wires that go to the rectifier, and connect them directly to the motor.

4/1/126:54 PM

Davy MacOGR Forum Member

Hi Guys, thanks for the help. Greatly appreciated . DAVY

4/1/127:03 PM

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