Electrical Relay: Types, Uses, Applications, Testing

When we say “relay”, people primarily associate it with a typical form of race. However, relay meaning in electrical is something else. A relay is an electronic switch that is used in a wide range of applications like automobiles (bikes and cars), industrial utilisation, home automation, test and measurement equipment, DIY projects and other applications. Unlike regular switches, an electrical relay is used to open and close two circuits with the help of an electrical signal. This electrical signal controls an electromagnet, which is responsible for connecting and disconnecting another circuit. If you’re looking for a relay switch, there are a variety of electrical stores available. Bringing in top-notch relay switches, Lauritz Knudsen (Formerly L&T Switchgear) is a one-stop solution for all your electrical requirements. Here, you can purchase different relay switches for protection, control and monitoring purposes. 

The relay circuit of Lauritz Knudsen (Formerly L&T Switchgear) is best suited for low—and medium-voltage power distribution systems. The brand uses modern technologies to make these relay switches, which can be used in various applications. Now that you know the electrical relay definition, let’s learn how many types of relays are available, along with their uses, applications, and testing. You will also get to know how relay switches work. 

Types of Electrical Relays

What is a relay switch is a common question among users. It is an electrical device that connects and disconnects circuits by receiving electrical signals from external sources. For instance, when one wishes to watch TV, one pushes the ON button on the TV remote, and an electrical signal is sent to the relay circuit inside the TV, turning the main power on. There are various types of relays based on contact type and applications. 

Electrical Relays: Contact Types

There are four types of electrical relays based on contact types:

• Single Pole Single Throw (SPST): The most simple and straightforward contact relay type. SPST relays have only one pole and may control a single circuit. The relay circuit can exist in either an open or closed state, and only one will conduct.
• Single Pole Double Throw (SPDT): A simple adjustment to the SPST relay. SPDT relays allow a single pole to switch between two positions, often NC and NO terminal, both of which conduct. This type of relay controls only one circuit at a time. 
• Double Pole Single Throw (DPST): Two paired SPSTs can be considered as DPST. While it can run two distinct circuits, each can only be adjusted to an open or closed state, with one of them conducting.
• Double Pole Double Throw (DPDT): This contact-type relay allows controlling two independent circuits, each of which may be adjusted to one of two conductive states. DPDT relays are the most adaptable of the main relay switches. 

Types of Relays Based on Applications

Do you want to know what is relay and its types based on applications? Here are the most common ones:

• Solid State Relay: Powered by a semiconductor, a solid state relay operates the relay’s switching mechanism. This is accomplished by sending a low-voltage optical signal from the semiconductor that permits the regulated higher-voltage load to operate when activated. These relays are known for their long run and fast functioning. However, when these relay switches create excess heat during semiconductor operation, it can cause problems. 
• Electromechanical relay: The most basic ones are electromechanical relays. They work with the regular electromagnetic coil, which can control the movable contact. However, this physical action takes longer and causes internal arcing, which might eventually destroy the relay.
• Reed Relay: Reed relays also operate like electromechanical relays; however, their design can be modified to reduce or eliminate frequent EMR concerns. These relay switches consist of two magnetic metal blades hanging inside the tube of inert gas with a coil. When the coil is triggered, the blades are attracted to each other, completing the circuit. This eliminates part of the damage that reduces the lifespan of standard EMR relays. However, they are slower and cannot carry as much current as SSR switches.

Uses/Applications of Electrical Relays

What is the purpose of using an electric switch? When you’re talking about using electrical relays, you simply use them to connect and disconnect circuits with the help of an electrical signal. 

One of the best advantages of relay is to protect the electrical system and reduce damage to the equipment attached to it as a result of overcurrents or voltages. Hence, relay switches protect the machinery to which they are linked. 

In applications like car starting solenoids, relays are used. These electrical switches are utilised to regulate a high-current circuit with a low-current signal. With the help of relays, one can identify and isolate the problems in power transmission and distribution systems. 

The following listicle offers the most common applications of electrical relay switches. 

• Traffic control
• Automotive
• Industrial process controllers
• Home appliances
• Computer interfaces
• Protection equipment of electrical power systems
• Motor drives control
• Lighting control systems

How Does an Electrical Relay Work?

The following relay circuit diagram shows how the electrical relay works. 

• The relay working principle is based on electromagnetic induction.
• When power is applied to the electromagnet, a magnetic field is created around it. 
• The above diagram shows how does a relay work when DC current is applied to the load. 
• The copper coil and iron core inside relays act as electromagnets. 
• When the power supply is withdrawn, it returns to its original position. This is known as the de-energising of the relay.

There are various relays with contact that are primarily closed and then opened when there is supply, which is the reverse of the relay that is shown in this picture. 

Solid state relays will contain a sensor element that detects the input voltage and changes the output via opto-coupling.

Testing an Electrical Relay

If you know what is the function of relay and you’re considering using it, testing the relay is very important. The process is simple and can be done at home with a little device. You can use a car’s battery or a multimeter to try the testing. However, serious bench testing requires a professional setup with a desktop power supply. 

Know How the Relay Works

After you’ve gathered information about what is relay, the next thing you need to know is how it works. There are various types of relay switches available based on contact and applications. The mechanism of all these switches varies from one another. So, when you’re testing the relay, know its type. 

Find the Relay

After you’ve done your research on the internet about testing a relay, the next thing you have to do is find it. The relay can be anywhere, depending on what it controls- beneath the dashboard, under the hood, in the fuse box, etc. 

Replace the Relay

The simplest technique to test a relay is to replace it with a known-good component. Relays are mostly inexpensive, but always having them handy may not happen. But be careful; whatever has triggered your first relay might do it for the second one as well if the problem has not been identified. 

Measure the Resistance

The next step demands you to take out your multimeter. You can prepare to test the relay in the vehicle or on a test bench. In any case, before you begin working, de-energise your relay by turning it off. To measure resistance, you have to turn the multimeter to ohms mode. Measuring the resistance of the relay means measuring the resistance between the two electromagnetic coils, which forms a Normally Closed (NC) circuit. 

Test the Continuity of Switch Pins

Once you have confirmed that the coil is functional, it is time to test the switch pins. These pins form a Normally Open (NO) circuit, which means they are always open and have no continuity. No current should flow through it until the circuit is closed by activating the relay. To test the continuity of the pins, set the multimeter to ohms and measure the resistance between the switch pins. 

Test the Energised Relay

After confirming that the relay works properly without power, you have to find out what happens when you add a little power to the mix. To test a relay, you can use a basic bench-stop power source. However, you can use a 9-volt battery or a 12-volt electricity from the automobile. You can now energise the coil pins. When you hear an audible click, it means that the electromagnetic coil is activated, and the internal switch shuts. If you don’t hear the sound, it means the switch pins are open and the relay is bad. 

Test the Voltage 

Just because the relay’s switch function works doesn’t mean the relay is excellent. You should still verify that the relay is supplying accurate voltage on the switched end to account for faulty or corroded contact points. Set the multimeter to DC volts and ensure you know the relay’s supply voltage. If you’re testing the relay with a bench-top power supply, you can see that on the unit. If you're using your car's battery, check the voltage across the terminals. With the activated relay and electricity given to one side of the switch pins, measure the voltage on the switch pins that have no wires connected to them. Even if not identical, it should be similar to the supply voltage. If it doesn’t work, replace the relay.

Read Also: What Is A Thermal Overload Relay?Types And Use Cases

Conclusion

A relay is an electrical component that is used to open and close two circuits with the help of an electrical signal. Now that you know what is the use of relay module, you must test the relay and the switch pins, following some easy steps. Relays are used in various protection and control systems in a wide range of applications, including automobiles, industrial utilisation, home automation and many more. If you’re looking for relays to equip low and medium-voltage power distribution systems, purchase them from Lauritz Knudsen (Formerly L&T Switchgear). From voltage and frequency relays to APFC relays, you will get hold of multiple relay types in this store.