What is a relay and how it works

By February 2, 2021 No Comments

What is a relay?

A relay is a very common component in modern automobiles. A relay is used when the vehicle circuit is unable to handle the amperage required to run an accessory.

Let’s take a look at the inside of a typical relay so we can better understand how they work. A relay consists of an electromagnetic coil and two circuits. Relays rely on a power trigger to energize the electromagnetic coil.  As the coil is energized it pulls a set of contacts together to complete a circuit activating the desired accessory.


What’s the difference between fuse and relay?

Different from a relay, which is more like a switch, a fuse is an autonomous protection device that interrupts the circuit when the circuit is abnormal and the current is abnormally high. A fuse will be cut off by its own to protect the electrical appliances which otherwise may cause a fire.

How to wire a relay?

how to wire a relay

Step 1: Terminal 30

Terminal 30 is where to connect the battery feed wire to. This is the power source coming directly from the battery. You should always use an inline fuse rated for the amperage of the accessory that you plan to power up.

Step 2: Terminal 85

Terminal 85 is one of our coil wires. It should be connected to a good ground source or it can be connected to a switch if you’re wiring it as a switched ground.

Step3: Terminal 86

Terminal 86 will be connected to our switch positive power. You should always fall DIN72552 standards which say that number 85 should always be the ground terminal

Terminal 87 is connected to the accessory that you’re planning to power up and is also known as the load

Terminal 87 a is only found in a 5 terminal relay and will have power to it when the relay is not energized this means that there’s no power to the terminal number 86 once the coil is energized the relay switches the power to the 87 terminal and the 87 a terminal will then lose its power.

Note: You should always consult an automotive amperage chart to help you determine what gauge wire you should use for your relay depending on the load itself and the length of wire required for installation on many of the newer vehicles.

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