I have a model locomotive that uses an RC Truck engine to power an alternator. The AC current goes through a bridge rectifier and then a RCE225 Bigger Dual Ended Switch (from Servo City) for Forward/Reverse control of two traction motors. I would like to send the power through another RCE225 dual ended switch to change the motors between series (for power) and parallel (for speed) wiring.

I need help with the wiring - I don't want to destroy an expensive component.

Thanks for your help!


  • \$\begingroup\$ Welcome to EE.SE. We don't know the specifications for the devices your are connecting. Please edit your answer to provide links to documentation on your switches and other components. If you read through the documentation, it may even provide recommended wiring diagrams. \$\endgroup\$ Aug 20, 2016 at 18:26

1 Answer 1


It's a relatively straightforward application of a DPDT relay:


simulate this circuit – Schematic created using CircuitLab

Just make sure it has a break-before-make contact configuration! You'll want to reduce power when changing this switch anyway, to reduce contact arcing.

  • \$\begingroup\$ Would you describe how current flows from + to - in the circuit that you provided in each switched state? \$\endgroup\$
    – DIYser
    Aug 20, 2016 at 18:49
  • \$\begingroup\$ Here is a link to the switch: \$\endgroup\$
    – Bob
    Aug 20, 2016 at 20:29
  • \$\begingroup\$ servocity.com/electronic-pwm-controlled-dual-relay-24amp \$\endgroup\$
    – Bob
    Aug 20, 2016 at 20:31
  • \$\begingroup\$ Here is the locomotive and train:youtube.com/watch?v=J2jbxTPkxiY \$\endgroup\$
    – Bob
    Aug 20, 2016 at 20:37
  • \$\begingroup\$ If you want to use another RCE225 the contact wiring is as per Dave's schematic. Essentially it is just a set of SPDT relays with a driver IC that works with RC PWM and some additional features. \$\endgroup\$
    – D-on
    Aug 21, 2016 at 2:23

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