Electromagnetic relay
An “electromagnetic relay” is an electrically operated switch which is used to control a high-power circuit using a low-power control signal.
Electromagnetic relay works on the principle of electromagnetic attraction, Where a solenoid coil is energizes to change the position of electrical contacts. Electromagnetic relays are widely used in control panels, PLC systems, and industrial automation.
This post is all about Electromagnetic relay. In which we will explain its construction, working & Types. But first we need to know why do we need electromagnetic relay ? Why should we use it ?
Why are we using electromagnetic relay ?
1. Different power supplies can get controlled through Electromagnetic relay
In Electrical power system, there are two supplies AC(Alternating Current) & DC(Direct Current).
- Whether it is AC or DC; They can not mix the power supplies with each other.
- AC supplies with different phase shifts also could not mix with each other.
- The DC supplies with different magnitude can not also be mixed.
- Each supply has its own flow path or flow circuit. To control another power supply with some another power supply we can use electromagnetic relay.
2. To Isolate one system from another
The output signal of Programmable controllers like PLC’s are soft in nature. That means these controllers produces output with having a low current rating. The heavy loads can not be directly controlled with the outputs of programmable controllers.
With electromagnetic relay, We can control the load indirectly. Plc first controls the relay and than relay controls load.
PLC–>ELECTROMAGNETIC RELAY–>LOAD
3. To control multiple outputs with single input
With electromagnetic relay, Multiple outputs can be controlled simultaneously at a same time with only one single input.
CONSTRUCTION OF ELECTROMAGNETIC RELAY
Electromagnetic relay consists of an electromagnet, NO & NC contacts & mechanical spring mechanism.
- Due to the spring tension, the contacts remain positioned at its normal position. That state is known as normal state.
- When an electromagnet get energized, These contacts changes their state. That state is known as forced state or actuated state.
- Further when electromagnet get de-energized, the contacts get back to their normal state due to mechanical spring tension.
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| 8 Pins Electromagnetic Relay by OMRON Coil 24VDC | Contact Rating 230VAC 10Amps(NO),5Amps(NC)-Resistive |
WORKING OF ELECTROMAGNETIC RELAY
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| Symbol of NO contact |
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| Symbol of NC contact |
- When an electromagnet get energized, the contacts get attracted towards the electromagnet Which results electrical contacts get changed.
- The relay is designed is such a way that all the present contacts get attracted as a single unit .
- When electromagnet get deenergized, all the contacts pushed back to their normal state because of the pull of mechanical spring arrangement.
- When electromagnet get energized(Forced state), common contact(3) get break with NC (4) contact & get shifted towards NO (5) contact.
- When electromagnet get deenergized(Normal state), common contact(3) get break with NO (5) contact & get shifted back to NC (3) contact.
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| Schematic Diagram of electromagnetic relay when coil is de-energized |
SELECTION OF ELECTROMAGNETIC RELAY
TYPES OF ELECTROMAGNETIC RELAY
14 Pins Electromagnetic Relay
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| 14 Pins Electromagnetic Relay by salzer Coil voltage 230VAC | Contact Rating-240VAC/24VDC, 5Amps |
LED as an indication for energized state
14 Pins Electromagnetic Relay by salzer
Terminals of electromagnetic Relay
14 Pins Electromagnetic Relay by salzer
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| De-energized State of Electromagnetic Relay 14 Pins Electromagnetic Relay by salzer |
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| Energized state of electromagnetic relay 14 Pins Electromagnetic Relay by salzer |
8 Pins Electromagnetic Relay
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| 8 Pins Electromagnetic Relay by OMRON Coil 24VDC | Contact Rating 230VAC 10Amps(NO),5Amps(NC)-Resistive |
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| 8 Pins Electromagnetic Relay by OMRON Coil voltage 230VAC | Contact Rating 230VAC/24VDC,5Amps |
PCB Mounted Electromagnetic Relay
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| PCB Mounted Electromagnetic Relay | Coil voltage 12VDC | Contact Rating 250VAC/28VDC,7Amps |
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| Base of PCB Mounted Electromagnetic relay having 1 changeover relay |
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| 14 Pins Electromagnetic Relay with 14 pins relay base |
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| 8 Pins Electromagnetic relay with 8 Pins relay base OMRON |
Applications of Electromagnetic Relay
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PLC output isolation
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Motor control
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Control panels
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Automation systems
Advantages of Electromagnetic Relay
- Compact
- Easy replacement
- Multiple contacts
- Multiple Types
DRAWBACKS OF ELECTROMAGNETIC RELAY
- IF compare with Solid State relays; Electromagnetic relays are slow in speed.
- After long use the contacts of the relay get carbonized which further don’t work precisely.
- Different type of Relays has their own base; if we need to change the relay sometime, Relay must be according to the base.
FAQs FOR ELECTROMAGENTIC RELAY
Q1. What is the function of an electromagnetic relay?
To control a high-power circuit using a low-power control signal.
Q2. What is NO and NC in relay?
NO (Normally Open) remains open in normal condition, while NC (Normally Closed) remains closed.
Q3. What is the difference between relay and contactor?
Relays are used for low current circuits, while contactors are used for high current loads.
Q4. What is the coil voltage of a relay?
Common coil voltages are 12VDC, 24VDC, 110VAC, and 230VAC.
CONCLUSION
- Electromagnetic relays are similar to Contactors which are having a electromagnet, mechanical spring mechanism & electrical contacts. But it is different from contactor because it is designed for small current ratings.
- There are different types of electromagnetic relays but basic function remains the same in all. The entire selection of electromagnetic relay depend upon the following parameters.