Auto Reverse Loop Control Question

I'm building an outdoor G Gauge layout that is two reverse loops connected by a single track main line. I am using the "spring switch" feature of the LGB turnouts to always route the train clockwise around both reverse loops. I am using the LGB #1015K Reverse Loop Set on each loop - this is essentially a bridge rectifier with the single track main line on the "AC side" and the reverse loop on the "DC side", so the polarity on the reverse loop is always correct for the clockwise operation. This leaves me needing to manually reverse the polarity of the main line each time the train get into each reverse loop.

I understand changing from DC to DCC would solve this problem, but I don't want to make that investment. I understand that there are automatic reverse loop controllers that would automate this. However, most seem to depend on either optical or magnetic sensing of the train to initiate the polarity change, and I would prefer to avoid this complexity outdoors.

A friend suggested that I could use a Digitrax PM42 Power Manager, even though I'm running DC. He explained that the PM42 senses the short circuit as the train exits the reverse loop into the unchanged main line and instantaneously reverses the main line polarity for the train's return trip. This sound ideal. Will the PM42 work this way on a DC layout? Has anyone done this? Are there any potential problems? I note that MRC makes an AD-520 DCC Auto Reverse which seems to do the same thing at a lower cost, but the MRC website says the AD-520 can not be used on non-DCC or DC layouts. Does anyone know why MRC imposes this limitation? Thanks, Geezer

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I see no reason in principle why either the Digitrax or MRC unit should not do what you suggest. There are two issues to bear in mind:

  1. You will get a polarity change whenever there is a short circuit on your main line, how often do you get shorts apart from those on the reverse loop?
  2. Forward and reverse on your controller will be wrong half the time.

If you can live with these issues give it a go. Keith

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DCC isn't going to fix that problem. Right now, you're reversing the direction switch hwile the train is in the loop. You don't have this ability with a normally wired DCC railroad unless you continue to use the reversing switch or an automatic switching circuit to reverse either the loop or mainline. The basic problem is that the layout is basically two wires and anytime that you get one wire in contact (anytime you run over the gaps between the main and the loop rails, you make contact with the other rail) with the other, you make a short. The really tough thing for you is that when the short happens on a DCC railroad, the power supply shuts off the power, whether until human interaction or an automatic reset interval happens, and that turns off the trains - more in the case of DCC because the one power supply is powering all of the trains running rather than just the one which shorted out.

-- Why do penguins walk so far to get to their nesting grounds?

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Bob May

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