4-pin relay

A 4-pin relay is an

 electromagnetic switch used to control a high-current circuit with a low-current signal. It typically consists of four pins that connect to different parts of the circuit. Here’s a breakdown of the 4-pin relay:

1.Pin 85 (Coil -):

 This pin connects to the ground or negative side of the control circuit. When a current flows through the coil (between pin 85 and pin 86), it creates a magnetic field that activates the relay.

2. Pin 86 (Coil +):

This pin connects to the positive side of the control circuit. Applying voltage here, relative to pin 85, energizes the coil, which then closes the switch inside the relay.

3. Pin 30 (Common):

 This is the common terminal of the relay switch, which is usually connected to the power source or load. When the relay is not energized, pin 30 is typically connected to pin 87a (in 5-pin relays), but in a 4-pin relay, pin 30 connects to pin 87 when the relay is activated.

4. Pin 87 (Normally Open - NO):

This pin is connected to pin 30 only when the relay is energized (the coil is powered). In its normal state (de-energized), pin 87 is not connected to pin 30. When the relay is activated, it closes the circuit between pin 30 and pin 87, allowing current to flow through to the load.

Operation:

- When a small current flows through pins 85 and 86, the coil inside the relay is energized, creating a magnetic field.

- This magnetic field pulls the internal switch, connecting pin 30 to pin 87.

- The connection allows current to flow from the power source through pin 30 to the load via pin 87.

 Applications:

Automotive:

 Used to control headlights, horns, or other high-current devices with a low-current signal.

Industrial:

 Used in control systems to switch motors, pumps, and other heavy loads.

Home Automation:

 Can be used to control appliances or lighting with low-power control signals.

This simple design makes the 4-pin relay a versatile and widely used component in electrical and electronic circuits.