Short circuits - 8 | Southport MRS

Motor driven point changing systems normally require two wires to each point. Power is fed via a two pole change- over switch which reverses the polarity across the motor, operating the motor in the reverse direction and changing the point. All that is required is a supply of 12 volts DC and one switch for each point. The diagram explains all.

Don't despair, there is a much more economical in wiring way to do it using that great saviour of us all, namely common return. First we need a power supply of +12 and -12v DC relative to a common earth. This can be derived from a single 16v AC source with the aid of two diodes and two capacitors. To control each point only a single pole change over switch is required. One terminal of the point motor is connected to the common earth and the other to the centre of the changeover switch. The other two terminals on the switch are connected to the +12 and -12v supply. Operating the switch changes the polarity of the connecting wire from positive to negative and the motor reverses.
As a bonus, if you connect a bi-polar (red/green) two leg LED in series with the wire to the motor, no resistor is required, and you will get an indication of which way the point is set.

SHORT CIRCUITS

8 Points of view - revisited