Tag: track wiring

Dale G. Kraus, MMR

Reverse Loops, Turntables, and Wyes … OH, MY!

(Apologies to Dorothy, Scarecrow, Tin Man, and Cowardly Lion.)

These three track alignments have been the bugaboos of model railroading since the invention of 2-rail DC wiring. Letting locomotives run through them smoothly and without shorting or stopping has required the use of toggle switches, relays linked to the position of switches and, for turntables, careful positioning of split pit rail pickup or similar installation on the central pivot shaft. While certainly a “do-able” method, the results were often fussy and required a lot of additional wiring.

Now we have it easy. Several manufacturers, Lenz, MRC, and Digitrax come to mind, have come out with a little magic box called the “Auto Reverser” which does the job without operator intervention.  How does it work?  Well…inside each device is a very tiny witch doctor with a machete and a large supply of minuscule chickens. When he senses the onset of an out-of-phase “short,” he quickly sacrifices one chicken and the problem goes away. (You’re buying this, right?) OK, OK! Actually there is a bunch of sensing circuitry and a fast-acting relay, but the first explanation is more fun. Each of these devices has a pair of “input” and a pair of “output” wires or screw terminals. The input is attached to the track buss and the output is attached to the “reversing section” or, through sliders, to the turntable rails.

The neat thing is, so long as the input and output wires are not attached “backwards,” i.e., hooking the input to the reversing section and the output to the buss, it does not matter which wire goes to which buss wire or rail.  The first loco to enter the section will properly align the reverser. If you do wire it wrong?  Not to worry; it just won’t work. The loco will just stop dead. If that happens, disconnect it and hook it up t’other way.

Now, keep in mind that this really is technology, not magic. The reversing section, be it loop, wye leg, or turntable track, must be completely insulated. Gaps must be placed in both rails at each end of the section and the turntable rails must not touch any of the approach track rails.  If there are switches in the reversing section, be sure that there are no “sneak circuits” through the switch. If there are, cut gaps beyond the frog in both rails of the diverging route. This will eliminate the “sneaker.” Be sure to feed the reversing section only through the reverser output.

One final thing: The reversing sections must be longer that the longest loco lash-up. For most of us this is no problem. If you are in N scale and insist on running mid-train and rear helpers, your reversing section needs to be short enough that the lead set and the first helper aren’t leaving and entering the section simultaneously. This will cause the witch doctor to have a schizophrenic episode and possible cut off his own head instead of the chicken’s. Smoke may mysteriously issue from the auto-reverser … NOT a good sign!

And please, DO READ THE INSTRUCTIONS!