How to Install an Electric Fan With a Relay and Switch

A relay is an electromechanical device that acts as a switching mechanism for a high-power electric circuit. Relay circuits are often used to control high-power circuits such power-transmission circuits. Relay circuits are also commonly used to control high-power electrical loads, such as electric motors and fans. An installed relay is turned on or off by means of a low-power switched circuit; when the switch on the low-power circuit is turned on, the relay is actuated and the path for electric current in the high-power circuit is completed.

Lead-acid battery, 12-volt, with L-type terminals
DC-powered electric fan
Electromechanical relay
Single-pole, single-throw switch with solder-type terminals
Electrical wire
Electrical pliers
Electronic solder
Soldering iron
Solder-type ring terminals
2 Machine screws, size 10-32
2 Machine nuts, size 10-32

Instructions

- 1
  Use the electrical pliers to cut six pieces of electrical wire 6 inches long. Strip half an inch of insulation from the ends of each wire piece.
- 2
  Place the switch in the “Off” position. Place one end of the first wire against one of the terminals on the switch. Use the soldering-iron tip to melt a small drop of electrical solder to both the wire end and the terminal. Smooth out the soldered joint with the soldering-iron tip until the soldered joint is shiny and free of lumps.
- 3
  Place one end of the second wire against the remaining terminal on the switch, and solder the wire to the terminal. Solder the loose end of the second wire to the “85” or “Coil A” terminal on the relay.
- 4
  Solder one end of the third wire to the “86” or “Coil B” terminal on the relay.
- 5
  Place a ring terminal over the loose end of the first wire, and solder the wire to the terminal. Place a ring terminal over the loose end of the third wire, and solder the wire to the terminal.
- 6
  Solder one end of the fourth wire to one of the electrical terminals on the motor. Solder the loose end of the fourth wire to the “30” or “Common” terminal on the relay.
- 7
  Solder one end of the fifth wire to the “87” or “Normally open” terminal on the relay. Place a ring terminal over the loose end of the fifth wire and solder the wire to the terminal.
- 8
  Solder one end of the sixth wire to the remaining electrical terminal on the motor. Place a ring terminal over the loose end of the sixth wire and solder the wire to the terminal.
- 9
  Place the ring terminals at the end of the third and sixth wires over the shaft of one of the machine screws. Insert the shaft of this machine screw into the hole in the negative-battery terminal. Place a machine nut over the shaft of this screw, and screw the nut on tightly to fasten the ring terminals securely to the negative-battery terminal.
- 10
  Place the ring terminals at the end of the first and fifth wires over the shaft of the remaining machine screw. Insert the shaft of this machine screw into the hole in the positive-battery terminal. Place the remaining machine nut over the shaft of this screw and screw the nut tightly on, to fasten the ring terminals securely to the positive-battery terminal.
- 11
  Move the switch to the “On” position. You will hear the relay click and the fan will begin to turn. Move the switch to the “Off” position to turn the fan off.

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