Model Forum / General / Railroads / February 2009

Can't speak for ZTC, but you'd need a reverse loop module with any NMRA
compliant DCC system.

John.

Even in DCC, you still can't connect the "A" rail to the "B" rail
without some kind of switching.

As other have stated, you can get auto reverse modules that will do
this automatically.

If he's running sound locos, the much longer break in the circuit as
you switch manually will play havoc, causing the sound decoder to go
through it's startup sequence again. foe the same reason you should
avoid relay based auto-reverers as they are often slow and you may
find the command station trips out before the revereser operates.

The autoreverser works by detecting a short circuit if the switched
section is currently at the wrong polarity and very quickly changing
the polarity to match that of the section the train is coming from.
When the train leaves the switched section, the polarity will change
again to math the exit tracks.

It's very important that the train cannot bridge between both entry
and exit sections and the switched section at the same time. The
simplest advice is to make the switched section longer than any train
but this rule can be relaxed if you know the nature of all trains that
will run through it (e.g. does the train have electrically linked
axles for carriage lighting?)

MBQ

It can be done manually with a switch, though as others have said an
auto-reversing module is the "standard DCC" automated way to do things.

A manual switch or a relay is considerably cheaper.
If the triangle-siding is a dead-end siding (or fan of sidings) and only
accessed from the triangle, then a switch or relay tied to the direction of
the turnouts leaving the triangle will do the job (on their outputs, most
auto reversing modules have a relay to switch the track polarity).

- Nigel