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Monday, May 23, 2011

To Trolley Pole Reverse Or Not To Trolley Pole Reverse.

That is the question.
Exploring the two methods of wiring a trolley. The "cool" method or the more practical method.

The question we get the most when the Southern California Traction Club displays its modules is "are the trolleys getting their power from the wires?". Not only are the guests pleased when we inform them that indeed they are, but we will also do a little demonstration of "Trolley Pole Reverse" that guests take a delight in. It doesn't take long for a trolley to come by. So I'll put my finger lightly under the overhead wire so that as the car comes by, the pole will disengage the wire and the car will roll to a stop. I'll stow that pole under the hold down hook and explain that "one pole is wired to one pole of the motor, and the other pole is wired to the other pole of the motor". Lifting the opposite pole to the wire, the car jumps to life and continues on its way ~ in the opposite direction. Guests are thoroughly impressed.

But lately we at the club have been discussing reliability. As all model railroaders know, the toughest electrical continuity to maintain is the contact between rail and wheel. The slightest obstruction will cause a stall. Stalls are no fun. With traction modeling not only is that problem made double with the tiny contact between the trolley shoe and overhead wire but triple so with the just as critical contact between the stowed pole and the hold down hook.

When a car stalls, its usually the tiny connection between the trolley shoe and overhead that's been compromised. A gentle tap of the overhead is usually enough to reengage to shoe to the wire. If that doesn't work then its probably the wheels, nudging the car forward a tad should fix that. If that doesn't work then a wiggle to the front pole might invigorate that contact. If that doesn't work... well, you get the idea. It gets a little frustrating. So eliminating weak spots like these just makes things run a little smoother. But eliminating the contact between the rails and overhead isn't feasible. But that connection between pole and hold down hook can be addressed.

With Trolley Pole Reverse, one trolley pole is wired to one pole of the motor while the other trolley pole is wired to the other pole of the motor. Whichever pole is in contact with the overhead will supply the positive charge to the motor. The other pole is in contact with the hold down hook completing the circuit by providing ground. This method requires good spring tension to press the pole up against the hold down hook and a clean connection between the pole and hold down hook. A little contact cleaner fluid is helpful here as well.

Though I've never heard it called this, I'm calling this method "Trolley Pole Forward", as opposed to Trolley Pole Reverse. This method eliminates the contact between the pole and hold down hook, providing a bit more reliable operation. This is particularly useful in a DCC environment where a car can be reversed without reversing the polarity of the rails and overhead. We simply tell the decoder to run the car the other way.

I think it all comes down to preference. On a point to point operation, Trolley Pole Reverse might work best. For a "roundy roundy" operation, Trolley Pole Forward might be preferred. On a DC layout, I think Reverse could be the way to go. On a DCC layout, Forward could be it. I don't know. But I think once my layout gets rolling, time will tell which I prefer. Yes sir! Time will tell!