Relays Type and its Working Principal


The relay is an electric switch. Which has some input and output terminals. The output single from the relay is controlled by supplying it to the input terminal. W can say this.

That a circuit is controlled automatically by relay. Relay is being used very much in the automation industry nowadays. If any device in any machine is to run automatically.

So we need a relay. It is used in our inverters, cars, bikes etc. These are of different types.

Who invented relay?

Telegraph was invented in 1831 by American scientist Joseph Henry. He presented the Telegraph in 1835 as a better version. So credit for Riley's invention goes to Joseph Henry.

Definition of Relay

The relay is just an electromagnetic switch. And it has a Side Coil. When there is a current flow inside it. So it works like Temporary Magnet. There are both types of relays ac or dc.

AC Relay 250VAC

For automation in the industry, relay is most commonly used. If there is any appliance running with main electric power in our house. And at that time if the power goes out. So our work is not done. We have to turn on the second source of power. Time is spent in doing this. To save this time, we use relay. And the self working of a tool is called automation.

Relay's Working Principle

Relay operates on a simple principle. When electricity is flowed in a close circuit, a magnetic field is formed around it which draws any iron thing towards itself.

The relay is used according to the same principle. When the coil of the relay is supplied. So she removes the inside armeter from nc and sticks it to no.

What happens in Relay?

There are different types of components inside a relay.
Which are as follows


It connects the armature inside the relay to the NO contact.


Yoke is on the outside of the relay, which prevents parts inside the relay from being damaged.

Spring Relay

When no supply is provided to the Spring-relay. Or say when the relay is closed. So it connects the armature to the nc contact.

Armeture Relay

Inside the armature-relay, the job of the armature is to connect the comman terminal with no contact and nc contact.


These are the input and output terminals of the relay. The device we have to switch. They are added to the terminal. It has the meaning of switching. To operate one device at a time and turn off the other.

What does Relay do?

Relay's working is very simple. When the relay is in off condition. So its common terminal is connected to nc contact. Because the spring inside him keeps pulling him further. And no contact is open as soon as we supply at the common terminal of the relay

So the armater inside it sticks to the no terminal.
The coil inside the relay, as soon as it is supplied, then removes the armature from nc and pastes it to no.

Type Of Relay

There are many different types of relay currently available. The use of relay varies everywhere. The type of relay depends on the reason it is operated. The type of relay we need. We place the same type of relay at the same place.

Based on the working principle.

Based on the working principle, the relay is divided into two parts. Semiconductor based relay.

Electromagnetic Relay.

In which electromagnetic relay is very much used.

You will find use of it in the car motorcycle inverter stabilizer etc. And semiconductor relays are small in size. This type of relay is used in small electronic circuits.

According to the number of poles

The relay consists of a commen terminal, 1 nc terminal and 1no terminal. But sometimes more than one input terminal and more than 1 output terminal are required.

Because we need to switch more devices, at that time we need a relay with two or more input output terminals.

  • Single Pole Single Throw
  • Single Pole Double Throw
  • Double Pole Single Throw
  • Double Pole Double Throw

Single Pole Double Throw

In the relay, you will get a no terminal and 1 nc terminal. You will connect the first water pump to the nc terminal as soon as your first pond is filled.

Your relay activates and nc becomes a terminal. Now your second water pump starts and the first water pump stops.

Relay on according to volt

Depending on the size and voltage, different types of relay are available in the market such as

For DC

  • 5 V DC
  • 12V DC
  • 24V DC

For AC

  • 110V AC
  • 220V AC
  • 250V AC
DC Relay 24v

Depending on the size and design of the relay many types of relays are available such as

  • Latching Relay
  • Vacuum Relays
  • Time delay relay
  • Mercury-wetted relay
  • Mercury relay
  • Overload Protection Relay
  • Force-Guided Contacts Relay
  • Multi-Voltage Relays
  • Safety Relays
  • Coaxial relay
  • Solid-State Contactor
  • Reed Relay
  • Polarized relay
  • Machine Tool Relay
  • Solid-State Relay
  • Static relay

What is the difference between DC vs AC relay?

Both AC and DC relays operate on the same principle as electromagnetic induction, but the construction is somewhat different. And it also depends on the applications. For which these relays are selected. The dC relay coil is employed with a freewheeling diode to de-energize. And the AC relay uses laminated cores to prevent eddy current losses.

This is a very interesting aspect of an AC. That for every half cycle, the direction of current supply changes. Therefore, the horoscope loses its magnetism for every cycle.

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