What are Model Rail Controllers?

Traditionally they are the device that controls the speed of the locomotive. Initially by altering the voltage, but in recent years digital enhancements have appeared.

The controlled power supply is connected to the locomotive motor through the tracks. Initially this was by using a third rail as the supply rail and the actual track as the return, exactly the same as a full size electric railway. Model railways tended to use a third centre rail, although some can use an overhead supply when that was used on the locomotive modelled.

The simplest method is a wire wound rheostat controlling a DC supply, reversing the loco by reversing the supply polarity. Until the arrival of electronics this was the most common method. A variation for the centre rail is to use studs, which are less obtrusive, but it does mean the loco needs a large skate pick up. It was often used on O gauge systems, especially those out of doors whwere the self cleaning created by the skate sliding over studs was very beneficial. For OO/HO while a number of companies used a third centre rail very few, and only one major manufacturer used the stud system.

Initially the voltages used tended to vary between manufacturers. Generally low up to 24 volts there were examples of mains voltages being used; for obvious reason this trend never caught on.

DC was popular as it meant batteries could be used to supply the current. However with AC becoming the standard for public electricty supples some systems were made using AC motors suppled through transformers and removing the need for rectification systems. Unfortunately AC motors have no polarity for reversing. Small AC motors can be reversed by swapping the supply connections to the brushes around. Practically this requires a switch on the motor and many systems used a switch activated by a pulse over the supply current. This hopefully reversed the motor direction. Practical controllers often required the central control handle to be quickly push in. As a system it works; which is really all that can be said about it.

Smaller, more efficient and cheaper rectifiers meant that AC was replaced by DC and the voltage of 12 volts became standard. Interestingly AC supply has made a comeback with digital systems with rectification and speed control now taking place on the loco controlled by digital pulses running over the AC supply.



Basic pulse controllers for low voltage are fairly cheap and readily available. All that is required to make a controller is a reversing switch and an auto resetting cut out. The latter can be a sperate unit, although the facility is provided on some control units. Some units even include an on/off reversing switch as well. A useful addon is a voltsge/amperage display.




Any suitable box will do and the controller can be either buit from scratch or purchased as a ready made unit.


12 volt DC SUPPLY


There are many units available. In practise a 15 volt unit may be of more use as this allows for any losses within the controller unit.