How Does an Electrical Relay Work?

Relays Defined

A relay is a type of switch used inside electrical circuits to control a large electric current with a much smaller one. Relays are used in many circuits including power supplies and counting circuits. Because relays have moving parts, they are not as durable or as fast as transistors, but they do have advantages in certain applications, because they waste less energy than transistors.

How an Electrical Relay Works

The most basic type of relay is an open switch with a springy metal contact. That contact is either made out of a magnetic metal, or has a magnet attached to it. There is a small coil of wire nearby the contact, which controls the switch. When current flows through the coil, it pulls on the contact, pulling the switch closed. When the current turns off, the magnetic field goes away, and the switch opens again. In many relays, this makes a click loud enough to hear across the room. That is why you will hear a click the moment before your fridge or stereo turns on.

Latching Relays

There are many specialized types of relays used for different electronic applications. One useful innovation is the latching relay. Like normal relays, the latching relay will close when a jolt of current passes through the coil. In latching relays, however, the switch stays closed until another pulse of coil opens it. This saves electricity, since the switch doesn't need a continuous flow to stay closed.