Turntable Wiring

[Les]

Query - is there a polarity issue when wiring a Walthers 90'  kit turntable.  When the turntable is turned 180 degrees the tracks are obviously turned around.  Does this present a polarity problem, and if so,  how is it corrected?  Thanks for your help.  Les

[rogertra]

Which Walters 90ft table?

The $250 one?

Or the crappy one?

[Les]

The crappy one

[rogertra]

Sorry, if it's the cheap one I think you may be on your own.

I'm sure that polarity is covered in the instructions.  I may still have mine, somewhere.  I'll see if I can fin them.

[CNE Runner]

I have the Atlas surface-mounted turntable and also was concerned about wiring it for DCC. The factory said to wire it the way the instructions said. NOT TRUE! The Atlas turntable has a built-in reversing "mechanism" to reverse the polarity of the turntable deck rails. All the operator notices is a pause in sound (or the headlight going out) when polarity is reversed. The instructions call for wiring all "B" lead in tracks polarity opposite that of the "A" track wiring...don't do this! All lead in wiring should have the same polarity (or there will be a short when the engine travels from the deck to the lead in track). I fully realize that you have a Walthers turntable; but I thought such a simple polarity fix would be already wired in. If your turntable deck rails get their power from the deck truck rail, you will probably see some sort of gap about halfway around the rails (actually there are two gaps equally opposite each other). The gap is where the poloarity is reversed. Again, if you are working in DCC, wire all lead in tracks with the same polarity. Hope this helps.

[Yampa Bob]

I did some research on this topic, the general consensus is to wire the lead-in tracks and the exit tracks at the same polarity. Then for DCC operation, it's simply a matter of hooking up an auto reverse module to the bridge rails. 

Taken a bit further, I am bashing an Atlas turntable to 12" diameter.  There are no wires connected to the bridge rails at all.  Instead, I'm installing small phosphor bronze wipers on the ends of the deck rails, and the ends of all the lead-in and exit rails. When the deck indexes, the bridge rails pick up power from either the lead or exit rails, so there is no polarity issue. The "Right Hand Rule" makes it automatic, for DC or DCC. 

Here's a typical scenario.  If the track is DC powered, run a loco (either DC or DCC) onto the deck, close the throttle. Rotate the deck (manual or motor) to the other 180 quadrant index.  Without even moving the controller direction switch, advance the throttle and the loco BACKS onto the exit rails. 

If using DCC power, then you need to change the direction switch to back onto the exit rails.  If you are merely reversing direction, just run on, rotate 180 and run off. With DCC power and a DCC loco, forward is forward regardless of orientation or polarity.

Remember the throttle is completely closed while rotating the deck, so the loco is essentially dead, no lights or sound at all.

I find it hard to believe that there seems to be no other reference anywhere detailing my method.  It's probably because "simple" doesn't make headlines or get published. 

Incidentally if your DC controller direction switch is labeled "forward - reverse", cover or remove the lettering.  Direction is relative only to how the wires are hooked up to the terminal section and loco orientation on the track.