How to Wire a Relay

How to Wire a Relay

When wiring a relay it is important to make sure you know how it works and how to connect the different pins. This is especially important if you are new to wiring and want to avoid any potential errors while working with a relay.

A relay is an electronic device that can change its state by energizing a coil inside it. The coil then carries current and switches the circuits off and on. A relay can be wired in many ways to control and switch various electrical components and devices.

Wiring Relays

Generally, a relay is wired with one wire from the battery to its positive terminal and another wire from the relay to the accessory that you wish it to switch on or off. This is to minimise the length of wire used and therefore reduce power loss, while keeping heavier wires out of the way of any accessories.

Relay pinouts are usually displayed in either square or round shapes, depending on the type of relay and may also be labelled with letters to help you identify them easier. The square layout is more common than the round for example as it’s much easier to work with, however the difference in this arrangement isn’t that significant and they both function identically.

How a Relay Works

The coil of a relay is an electromagnet that can carry high current, but when it’s de-energised it collapses the magnetic field which then causes the armature to open and close. This naturally connects the relay points and turns the circuit on or off, just like a switch on a wall.

A diode is often attached across the coil of a relay to absorb any of the large voltage spikes that occur when the electromagnetic field collapses on de-energising of the coil. This prevents the transistor that controls the relay from getting damaged, as well as preventing any of the relay’s back EMF escaping and entering the power supply or other parts of the electrical system that it’s connected with.

You can use a resistor in place of a diode for this purpose as well, but it’s not quite as effective in suppressing the voltage spikes. You can also use a capacitor in this way, but this has some disadvantages.

How to Test Relay Functionality

The best way to check whether a relay is working is to connect it to a test lamp and then use a circuit tester to see if current is reaching the relay’s N/O contacts or its feed terminal. If the tester lights up, the relay is working properly and you can go ahead and start wiring it.

Using a relay isn’t complicated, but it’s important to make sure you’re wiring it correctly and avoiding any possible mistakes that could lead to a short or power surge. This can damage your vehicle’s wiring and cause an accident.

Relays can be controlled in a variety of ways, and it is also possible to have multiple relays controlling the same circuit. This is known as relay logic or ladder diagrams and is a simple, but effective way to control an electrical circuit.

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