Making Your Model Rolling Stock "Visible"

Model Railroad current-sensing occupancy detectors work on the premise that currents flows between the rails.  Prototype railroad occupancy detectors work the same way.  However, the prototype wheelset creates a dead short between the rails when a train occupies a block.  Obviously, we cannot short the rails because model locomotives pick up power from the rails so the rails must remain isolated from one another.  Locomotives and lighted rolling stock inherently permits current to flow between the rails via the motor or bulbs.  However, unlighted rolling stock does not allow any current to flow between the two rails and is designed with some type of  mechanism to insulate the rails from each other; either the wheels are made of plastic, the axle is plastic or an insulated bushing is installed where one or both wheels attach to the axle.

Plastic wheelsets do not provide a viable starting point for making a detectable wheelset and; therefore, should be changed out with a metal wheelset.  Now the problem of bridging the insulation mechanism on the metal wheelset still exists.  As stated earlier, a straight jump of the insulating mechanism is not possible as this will create a dead short.  Therefore, the next best option is to install a small SMT-style (chip) resistor across the insulating barrier, albeit a plastic axle or bushing.  The resistor provides an adequate electrical insulating barrier but still allows a minute amount of electrical current to pass between the rails that can be detected by the occupancy circuit.  To learn how to add resistors to wheelsets yourself or where to find R-T-R resistor-equipped wheelsets, view the file below:

wheelset resistor.pdf

170 Kb


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