KB282: Auto Reversing Mistakes

This article was last updated on May 8, 2012, 3:54 p.m. | Print Article | Leave Feedback

Problems occurring on most auto reversing sections are a result of improper wiring or gapping.

Digitrax auto reversing units such as the PM42 or AR1 require a "hard" short which means there must be good current flow to both sides of the gaps, on the reversing section side and on the "normal" side.

Our experience has been that over 90% of reversing section problems are a result of improper wiring or improper gaps.

Another 5% is a result of improperly wired or configured auto reversing units.

It is poor practice to put the gaps immediately behind a switch (turnout in model railroad talk) and to rely on the points of the switch to supply the current to the "normal" side of the gaps leading to the reversing section.

Resistance through those points often reduces the current to the point a good short cannot occur, preventing the auto reversing unit from doing it's job.

On long reversing sections to few track feeders from the auto reversing unit can prevent enough current on that side.

Relying on current through the track itself, particularly rail joiners, is not wise as rail joiners are notoriously poor conductors of current.

One of the biggest mistakes made is in the gaps themselves.

The wheels of the rolling stock MUST be able to make contact with BOTH SIDES of the gaps simultaneously to get the necessary short to activate the phase change in the auto reverser.

This means you cannot have insulated rail joiners that come above the rail or even level with the top of the rail as these prevent the wheels from simultaneously contacting both sides of the gaps.

Was this article helpful? Send us feedback!

Please let us know if this article was helpful to you.

Please leave a detailed message below.