A relay is handy whenever you want to control a relatively large electrical current or voltage with a small one. For example, you can safely run low voltage from a push button micro switch at one end of your house to control a relay at the other end, where it locally operates a 120V motor. Wiring the micro switch to control the relay is relatively simple and straightforward. You need to identify which of the relay's pins belong to its coil and contacts, and use the switch to control power to the coil.
- Skill level:
Things you need
- SPST micro switch
- 12-volt DC relay
- 22-gauge wire
- Wire strippers
- 30-watt soldering iron
- Electronics solder
- 12-V DC power supply
Examine the body of the relay and determine which pins power the coil. Determine the polarity of the pins. The relay will have a diagram on its top or front face sketching its pin layout. Two dots with a bar, coil or zigzag between them indicate the coil pins. Two or three dots between that look like an electrical switch symbol are the switched pins. The diagram will indicate polarity with a plus and minus sign.
Cut two lengths of 22-gauge wire that will carry direct current (DC) to the relay from the micro switch. Cut one more length of wire about 5 inches long. Strip 1/4 to 1/2 inch of insulation from each end of the wires.
Connect one end of the 5-inch wire to the positive terminal of the 12V DC power supply. Solder the other end to one of the micro switch's solder lugs. Solder one end of one of the longer wires to the other micro switch solder lug. Solder the other end to the positive coil pin of the relay.
Solder one end of another long wire to the negative relay coil pin. Connect the other end to the DC power supply's negative terminal.
Plug the power supply into an AC outlet and turn it on. Press the micro switch repeatedly. You should hear a clicking sound from the relay as its contacts open and close.
Tips and warnings
- The relay will have a diagram on it indicating which of its pins put power to the coil, and which go to the contacts. It will also indicate the polarity of DC going to the coil.
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