A relay is a device that is used for controlling high voltage and current from low voltage. Electrical relays and contractors use a low-level control signal to switch a much higher voltage or current supply using a number of different contact arrangements.
The term Relay generally refers to a device that provides an electrical connection between two or more points in response to the application of a control signal. The most common and widely used type of electrical relay is the electromechanical relay or EMR.
Normally most of the DC relay has 5 pins. Two-pin are connected to the relay coil .while the other three pins are common, Normally open “NO” and Normally Closed “NC”
DC relay comes in deferent voltage rating in both coil voltage and load voltage. The coil voltages are 5v, 6v, 9v, 12v, and 24v mostly use.
Working principle of DC relay:
At normal state when there is no power applied to the coil of the relay the common point is connected to the Normally closed point .thus the common pin and NC pin are short circuit.
when we apply power to the coil .the coil energies and become magnetized which attract the strip from NC point toward the NO point thus the Common pin connected to the NO pin.
When the power removes the spring connected to the Metal strip bring back the metal strip to its original NC position. Both the coil and Load power are isolated from each other inside the relay.
• An electromechanical switch is termed as Relay. It reacts as an Automatic switch to manage (just ON/OFF) large voltage load by using a low voltage signal. we tend to use DC (Direct Current) provide to energize electromagnetic coil placed in relay thus, it’s referred to as DC relay switch.
• You know what happens when AC supply is given to the coil, there will be varying magnetic field not suitable for constant switch (ON/OFF) operation that’s why here DC used.
• The Relay has Electromagnetic Coil turned around a metal piece this will reacts as a magnet when the coil gets energized. Movable Armature attached with spring exactly placed above the electromagnet setup and makes contact between the common terminal and Normally closed contact (N/C), without any supply or zero input supply, this condition may be termed as a normally open relay. When the coil gets energized movable armature attracted by an electromagnet and N/O contact becomes closed and N/C becomes open.
How to use Relay in Circuit:
A typical application circuit is given for DC Relay switch. The magnetic coil is connected between bias through switching transistors. To protect the coil from back emf flywheel diode placed in reverse bias across the coil. The input Vin to the switching transistor base makes conduction through transistor hence the coil connected to bias directly. It makes coil energized when Vin downs transistor comes to cutoff and disconnects relay coil from bias.
Electrical relays and contractors use a low-level control signal to switch a much higher voltage or current supply using a number of different contact arrangements
Electromagnetic relay types:
A relay can be found in different forms, depends on the switch contacts, poles, and throws. Single pole single throw (SPST) a single switch and the contact is normally open or normally closed. Single pole Double throw (SPDT) is the most common relay used for electronics projects and it has N/O and N/C contacts. Double pole type relays have two contacts either close or open the same together.
Uses of DC Relays:
1: DC relay use as an automatic ON and OFF switch.
2: Use for controlling High power from low power.