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How to Use Solid State Relays to Reverse a Motor

Solid state relays use thyristors or MOSFETs as electrically-operated switches. They let computers, which usually supply little power, control motors and other large devices by switching those devices into a circuit with an external power source. Solid state relays offer advantages over their electromechanical cousins such as faster switching time, longer lifetimes due to no moving parts and better resistance to shock and electrical interference. Most importantly, solid state relays instantly create a stable connection, while mechanical relays suffer from contact bounce.

Things You'll Need

4 solid state relays
Copper wire
Electric motor
Microcontroller
Power source

Instructions

- 1
  Wire the positive terminal of your power source to pin 1 on the first relay. Pin 1 is usually a small metal screw on the corner of the relay with a 1 next to it. Then wire pin 2 of this first relay to one of the motor's terminals, which looks like a small metal screw on the motor's housing.
- 2
  Wire the motor's other terminal to pin 1 on the second relay. Then wire pin 2 on the second relay to the negative terminal of the power source. This completes a circuit that will drive the motor forward. For future reference, the relays used in steps 1 and 2 will be referred to as relays 1 and 2.
- 3
  Construct a second circuit identical to the one outlined in steps 1 and 2 using the third and fourth relays, except switch the wires connecting the positive and negative terminals of the power source. This will create a second circuit that drives the motor in reverse.
- 4
  Wire pin 4 on each of the relays to the same ground the microcontroller uses.
- 5
  Connect pin 3 on each of the relays to different output pins on the microcontroller. Note which relay connects to which output.
- 6
  Program the microcontroller to turn on relays 1 and 2, wait one second, turn off relays 1 and 2 then turn on relays 3 and 4. This will drive the motor forward for one second, then reverse.

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