Relays are electromagnetic switches that are operated by a small electric current. These have the ability to turn on and off similar to that of a larger electric current. When the building process of the relays has been completed they take on the appearance of a lever. When the switch is on, the tiny electric current flows and turns on another appliance that uses a larger current. These relays have been used in many different devices and even early forms of computers used them. In present times, they are used in various electric motors and household items, such as lamps.
The Construction of the Relay
The electromagnet part of the relay is made from a coil of wire which has electric flowing through it. The electricity causes gives it the magnetic properties. This magnet is used to link two circuits together. There is an input circuit located on one side that receives power from a sensor or a switch. The current is fed to the electromagnet when the circuit is turned on or activated. The electromagnet closes the metal switch next to it – a part of the second circuit called the output circuit – activating this one also.
How the Relay Works
The input circuit is originally in the off position. This means that the switch is open and there is no electric current flowing through it until the switch closes. The output circuit is also in the off position with the switch open.
When the small electric current passes into the input circuit by closing the switch, the electromagnet represented by the coil of wire is activated. This creates a magnetic field that surrounds the coil.
The electromagnet, when it is surrounded by the magnetic field pulls the output circuit which is made of metal, towards the magnet, therefore closing the circuit. This allows the much larger electric current to pass through the activated output circuit.
At the time that the switch is opened once again, the electric current ceases to flow through the input circuit. This removes the ability of the electromagnet to create the magnetic field thus also cutting off the larger electric current feeding through the output circuit.
Differences between Relays
The basics of how relays work are technically very similar amongst the whole group. There are however some differences between them that are important to know about. There are relays that can be built or purchased that are normally in the ‘off’ position. There are also those that are normally in the ‘on’ position but the majority are not. Those that are in the ‘on’ position have closed circuits all of the time unless the operator of the switch opens them.
For any type of relay, it is important to understand what the maximum voltage is that can pass through it. Using too much voltage with the relay can cause electrical mishaps including a burnout in the circuit or switch.