What Are Relays?
A relay is a component with the function of a switch that turns on or off a subsequent electrical circuit by means of an electrical signal received from an external source.
Unlike manual controls, such as lighting that are turned on and off with a pushbutton, automatic controls require electrically operated contacts. For this purpose, relays are used, whose contacts are operated by electromagnetic force.
A relay is a device that opens or closes an electric circuit by electromagnetic force, and depending on the set capacity, can control even large loads. They are also called electromagnetic relays.
Types of Relays
Relays can be divided into two main types: contact relays and non-contact relays. Contact relays are also called mechanical relays, and non-contact relays are called solid-state relays (SSR).
1. With Contact Relays
Contact relays consist of a coil wound around an iron core and an electrical contact that turns the current on and off. When electricity flows through the coil, a magnetic field is generated, which attracts the metal contacts and energizes them when they make contact. The operation of the electromagnet and contacts are mechanically linked, but electrically separate. For example, the contacts of a relay operating at a voltage of 24 VDC can be used to light a 100 VAC light bulb.
2. Contactless Relay
A relay that does not have mechanically operating components like a contact relay. It consists of electronic components such as photodiodes, light-emitting diodes (LEDs), and TRIACs and thyristors, which are a type of power semiconductor. The basic principle is that the photodiode receives the light generated by the current flowing through the light-emitting diode and current flows through it.
Role of Relays
Relays can switch large currents on and off with a small amount of current.
- When operating electrical equipment that consumes large amounts of current, such as motors and heaters, there is a risk that a large inrush current will flow through the operating switch if it is left in place, causing it to overheat or burn out. By inserting a relay between the switch and the load, such hazards can be prevented. It also prevents electric shocks to people operating electronic equipment.
- Inserting a relay between an electrical device and a battery shortens the wiring through which large currents flow and reduces resistance. In addition, since only a small current flows between relays and operation switches, they can be connected using thin wiring, greatly reducing power consumption.
Because relays have such a variety of effects, they are used in a wide range of applications, including in-vehicle, communications, home appliances, and factory control equipment.