At EMRC we use two battery chargers ( with modifications) to power our trains. We use a split potential power system that means -12V DC 0V + 12V DC. In effect you are using one transformer in one direction, and the other for the reverse direction.
At EMRC we use a simple yet effective controller. It is a mechanical/electronic controller. They have been used since the club's inception back in 1980.
The controller is a development from kits originally purchased from the Melbourne Model Railway Society and were modified by removing the jug style of element from the circuit and replacing this with diodes connected in series. This allows for a smoother operation of locos by varying the voltage rather than the resistance. They have been always been cheap to construct.
Basically the controller has a mechanical lever that moved a wiper around a circle of bolts which have diodes attached. As you move the controller around the wiper increases the diodes in the circuit.
It relies on the electronic characteristic of a normal everyday diode. A diode will always drop the voltage by about .5 of a volt, independent of the current. The controller adds the diodes into the circuit thereby reducing the voltage down in discrete steps.
The controllers control voltage independent of the current required. Slow speed is performance is satisfactory. The controllers work well with all types of locomotives.