A double pole double throw (DPDT) switch is a three-selection electrical device in which there is one "off" and two "on" positions. An application for this switch is for reversing a direct current (DC) electrical motor. The motor's two-power leads are reversed at one of the switches screw terminals. This allows the DC power to be reversed going to the electrical motor. This action then reverses the motor's direction. Attention must be paid to the allowable power capacity of the switch. In all cases, the switch is plainly identified on the side or rear of the switch mechanism.
Identify the six screw terminals on the side or rear of the switch. There are three pairs of screws that will conduct the electrical power through the switch's mechanism and contacts. The two terminals in the very middle are the power feed connections. The four outermost terminals conduct power to the device being controlled.
Remove all electrical power from the power source. Use the wire strippers and remove 1.8 cm (3/4 inch) of the wires' insulation to reveal bare copper. Do this on all wires that are being connected to the DPDT switch. Connect the positive (+) power wire from the power supply to one of the centre screw terminals. Tighten the screw with a screwdriver. Attach the negative (-) power wire from the power supply to the other centre screw terminal.
Attach the two motor leads to one each of the outer screw terminals on the DPDT switch. It does not matter which motor lead is connected to which screw terminal.
Strip each end of the two 7.5 cm (3 inch) long wires. Using a screwdriver, connect the short wires to the other outer screw terminals on the DPDT switch.
Connect one of the short wires to the screw terminal on the DPDT switch that one of the motor leads is attached to. Cross the wire over so it is on the opposite side of the switch's screw terminal. In other words, you are crossing the wire over to make the reverse connection for current flow. Perform the same action with the other short wire by connecting it to the other motor lead.
Apply power from the power source. Move the switch in one direction. The motor should be running. Move the switch to the centre position, and the motor is now off. Move the switch in the other direction, and the motor should now be running in a reverse direction. If the motor fails to reverse direction, simply exchange the two short wires in their positions on the switch's screw terminals.
Do not connect or service any electrical device while power is being supplied from the power source. Damage to equipment or personal injury can occur.
Things you need
- Wire strippers
- DC power source
- DPDT switch
- Electrical device (motor)
- 7.5 cm (3 inch) wires (2)