Polarity reversal switches consist of one or more mechanical switches wired together to provide two or three functional states, typically forward, reverse and off. There are several circuits yielding polarity reversal capabilities and each has its own advantages.
- Skill level:
Things you need
- 2 DPST momentary-style, spring loaded switches
- DC motor or other polarity sensitive device
- Wire cutters
- Soldering iron
Wire the "normally closed" terminals of both switches together with a soldering iron.
Wire the "normally open" terminals of both switches together.
Connect the negative terminal of the battery to the "normally closed" terminals of the switches and the positive terminal of the battery to the "normally open" side.
Connect the two remaining pins, one common from each switch, to the motor.
Test the circuit. Assuming that the battery is good and all of the wiring is correct, triggering switch 1 will activate the motor in the forward direction. Releasing switch 1 and triggering switch 2 will cause the motor to spin in reverse.
Tips and warnings
- Secure the switches in a vice or mount them in a finished panel if you are a beginner. It is typically cumbersome to wire multiple connections to a switch.
- You will need to understand the switches. DPST means "Double Pole, Single Throw." The type required in this circuit uses three terminals, "normally closed," "normally open," and "common." The switch "toggle lever" should be spring loaded to maintain a normal state, which is defined as "off." When actuated by the user, the state is considered "on."
- Due to the two-switch design of this circuit, it is possible to have two additional states of operation, "both switches closed" and "both switches open." These two states cause the outputs to the motor to become short-circuited, meaning the resistance measured between the motor will drop to essentially zero. This behaviour would not be apparent when driving a bicolour LED. However, when driving a DC motor, these two states would force the motor to stop spinning abruptly, acting as a magnetic brake. This is desirable for circuits involving actuators and car power windows, since the user usually wants the movement to cease after releasing the switch.
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