The reversing loop is a simple way to reverse the direction of a train by traveling around a loop of track to the starting point. In model railroading, it is usually used for installing a track loop in a limited space, and turning the train around so it can return on the same track it arrived on. This presents a problem since a complete track loop on a DC powered train would produce a track short circuit. The answer to this situation is to electrically isolate the loop itself so the polarity of the connecting track can be reversed for the return trip while the train is traveling around the loops or main line.
Powering the Loop Track or tracks
While powering the loop directly from the track power supply is the simplest method, it has the disadvantage of limiting the train to traveling the loop in only one direction. However it does have the advantage of allowing switching, station stops, and other activity while the train is present on a loop or the main line. The use of a bridge rectifier to power the loop track is an alternative, but while it simplifies the track wiring a little, it adds an extra device. Also, because of the inherent voltage loss in a bridge rectifier, it produces a noticeable slowing of most locomotives while traveling around the loop, and the trains cannot reverse direction. A third method is to power the loop track with a DPDT supplementary switch piggybacked on the track switch at the entrance of the loop. The switch can easily be wired to reverse the loop polarity whenever the track switch is thrown to change the track direction. The track switch can be thrown with manual switches or two magnetic switches located at the entrance of both ends of the loop. The magnetic switches, whether used with either the Realroad's "Magic Switchman" or LGB's EPL system, can cause the train to reverse direction on each successive pass around the loop track.
Methods of Automatic Track Reversal
There are many ways to reverse the polarity of the connecting track but, by far the simplest way is the Realroad's Magic Motorman. Because it senses the arrival of the train, it automatically reverses the track polarity before it is required. It also has internal relays to reliably control the switches to the main track and loop entrances. Simple reversing loops can operate with spring loaded manual track switches but powered switches are always a good idea outdoors. Wiring the Magic Motorman with spring return switches is a breeze. Here are some simplified instructions:
1. Wire both loops, or one if running a single loop, in the direction you wish the train to travel.
2. Set the switches so an approaching train enters the loop in the direction it's supposed to travel.
3. Leave the train off the track and turn on the power. Wait about 20 seconds and put the train on the reversing section. If it doesn't run in the direction you wish, shut it off and reverse the two connections to the track. Repeat this step if you reversed the connections.
4. It should now be running in the direction you prefer and it should run normally.
NOTE: If the train is located on the first loop when started, don't let it enter the reversing section until the Magic Motorman has had a few seconds to set the track correctly. If the train is located on the second loop, back it up manually with the controller until it's on the reversing section then reverse the controller. If started on the reversing section, it will run toward the first loop and, depending on when it was shut off last, there is a 50/50 chance it will be running backwards. Let it go until it has gone around the loop and is fully back on the reversing section. Then, turn off the power and then turn it back on, It should again move toward the first loop only, this time it will be traveling forward.
The least expensive way to build an automatic reversing loop is using an LGB track switch with a supplementary switch attached, and wired for track reversal. The main line is then reversed whenever the track switch is thrown to receive an arriving train. The track switch can be controlled by either LGB's EPL system or, preferably, the Realroad's more reliable "Magic Switchman". Both are controlled by a pair of LGB's 17100 reed switches located at each end where the train will operate one of them just before it crosses a switch.
Because of the ability to create electrical short circuits, manual operation of reversing loops is not recommended. Also, the use of the Realroad's "Magic Guardian" is always a good idea. It constantly monitors the track conditions and stops an arriving train if the track conditions are incorrect. They're good insurance on any reversing layout.
The Realroad's Magic Reverser, although not having the ability to provide station stops on the reversing section, is probably the best choice where steel wheels and lighted cars could cause electrical problems.
