A relay is an electrical component that uses one power source to switch another power source. It has a coil and a set of contacts.
For example a voltage of 24 volts at low current could be used to switch a voltage of 380 volts at higher current thanks to the use of a relay.
How Relays Work
A relay works much the same way as a contactor, it has an electrical coil and a set of contacts. When voltage is applied to its coil, it will energise and create a magnetic field. This magnetic field then acts on the contacts and switches them over. If the contacts were normally open in their resting state they will now be closed during the coils energised state (and vise versa for normally closed). The relay also has a spring, so when the coil becomes de-energised the spring pull the contacts back to their original resting state again.
How Relays Are Used
Relays can be used in electrical circuits where you might want to use one particular voltage to switch another voltage. This is sometimes done when smaller safer control voltages are used to switch higher voltages that energise larger contactors. In the above circuit we can see that when the start button is pressed the relay coil directly below it (R1) becomes energised, this in turn closes the R1 contact on the right of the picture. Then K1 is energised which will eventually power up the motor.
Shapes And Sizes
Relays can come in lots of different shapes and sizes, they can have one set of contacts or many different sets of contacts. Their coils can be designed to operate on many different voltages. And, timing relays such as on delay and off delay are also available.
To Recap
A relay is an electrical component that has a coil and a set of contacts. When the coil is energised, the contacts change state.
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