Construction of 4-pin relay
Usually there is a plastic or metal casing that serves to protect the internal components.Internally, it contains key components such as coils, iron cores, armatures, and contacts.
The structure diagram of the relay is as follows：
Principle of 4-pin relay
Therefore, when a 12V DC voltage is applied to both ends of the coil, a current flows through the coil. When there is current passing through the coil, a magnetic field is formed according to the rules of electromagnetic induction. This will attract the iron core towards the magnetic field, and the iron core will drive the movement of the armature. The movement of the armature changes the contact state of the relay, achieving on/off control of the circuit. For example, normally open contacts should be closed; Normally closed contacts should be open.
Below, we will further understand through the relay wiring diagram and textual explanation
1.When we apply a certain amount of current and the relay starts working, when the COM terminal of the relay changes from NC to NO, a closed circuit is formed, and the relay controls the power supply to turn on the relay
2.When the current we apply exceeds the maximum capacity of the light bulb, the relay will close. When the COM terminal of the relay changes from NC to NO, the closed circuit is disconnected, and the relay control power supply is disconnected
Function of 4-pin relay
A 4-pin relay generally has two main parts, and the four pins have the following functions:
Control section (coil)
Two of the pins are coil pins, which also cover the function of connecting and controlling current. Before applying an appropriate voltage to both ends of the coil, current will flow through the coil and generate a magnetic field to power its working relay.
Controlled components (contacts)
For example, the other two feet are contact pins, such as terminals 87 and 30. Driven by the magnetic field generated in the coil, the relay contacts will move to achieve the purpose of switching the circuit on/off. There are two common forms of contacts: normally open contacts, where the coil opens when not powered and then closes when powered on; Normally closed contacts, where the coil closes when not powered and opens when powered. This usually means that terminal 87 is connected to a normally open contact, while terminal 30 is a common terminal that can be connected to terminal 87 or another normally closed terminal depending on the status of the relay.
Wiring method of 4-pin relay
Automotive Circuit
Wiring method for car fog lights:
Line 85 is connected to the headlight control line, which provides a trigger signal for the relay when the headlights are turned on.
Connect the grounding wire (negative pole) at 86.
Connect Line 30 to the positive pole of the battery (the wire with a fuse) to obtain power.
Connect the fog lights on the 87th and control the on/off of the fog lights.
Wiring method for car horn:
Connect the horn switch control line to Line 85. When the horn switch is pressed, the relay coil is energized.
Connect to the grounding wire on the 86th.
Connect the positive pole of the vehicle power supply to Line 30 to ensure a stable power supply for the relay.
Connect horn 87 and control the horn to produce sound.
Wiring method for car starting circuit:
One foot grounded (equivalent to pin 86 grounded).
The other foot is connected to the ignition switch start gear (which can be seen as pin 85 receiving the control signal).
The other two pins, one is connected to the live wire (similar to the positive terminal of the power supply on wire 30), and the other pin is connected to the starter magnetic switch (corresponding to pin 87 connected to the load).
Industrial automation control
Control motor wiring method:
If using a DC motor: Connect the positive pole of the DC power supply to one coil pin of the relay (such as pin 85) and the negative pole to another coil pin (pin 86). The positive pole of the motor is connected to the normally open contact (No. 87) of the relay, and the negative pole of the motor is connected to the common contact (No. 30). When the relay coil is energized, the normally open contact and the common contact are closed, and the motor is powered on to operate; The coil loses power and the motor stops.
For AC motors: Connect the live wire of the AC power supply to the normally open contact 87 of the relay, and connect the neutral wire to the common contact 30 to connect the AC motor. In addition, the control terminals of relay coils 85 and 86 must be connected to corresponding control signals, such as PLC output signals, which are responsible for commanding the start and stop of the motor.
Lighting control wiring method:
DC powered lamps, such as LED strips, have a normally open contact 87 connected to the positive pole of the DC power supply, a common contact 30 connected to the negative pole, and control terminals connected to coils 85, 86 of corresponding control devices such as switches or sensors. When the control device sends a signal to energize the relay coil, the light will turn on; When the coil loses power, the light goes out.
For example, in order to control AC powered lamps such as regular incandescent or fluorescent lamps, the live wire of the AC power supply is connected to the normally open contact 87 of the relay. The neutral wire is connected to the common contact 30, and the coil control terminals 85 and 86 are connected to the control signal as needed to achieve on/off control of the lamp.
Control valve wiring method:
For pneumatic valves, the air source is usually connected to the inlet of the valve, the control signal interface of the valve is connected to the normally open contact (No. 87) of the relay, and the common contact (No. 30) is connected to the signal ground or the negative pole of the power supply. The relay coils (85, 86) are powered on or off according to the instructions of the control system, thereby controlling the opening and closing of the valve.
The control method of electric valves is similar, connecting the control power line of the electric valve to the normally open contact (No. 87) and common contact (No. 30) of the relay, and controlling the action of the electric valve through the on/off of the relay.
Intelligent Home Furnishing system
Intelligent curtain wiring method:
The live wire of the 220V AC power supply is connected to the normally open contact (No. 87) of the relay, and the neutral wire is connected to the common contact (No. 30). Connect the power cord of the curtain motor to the output terminal of the relay. The relay coils (85, 86) are connected to the output signal terminal of the smart home controller. When the controller sends a command to open the curtains, the relay coils are powered on, the normally open contacts are closed, and the curtain motor is powered on to operate, opening the curtains; Close the curtains in the same way.
Smart home appliance wiring method:
Taking the smart air conditioner as an example, cut off the power plug of the air conditioner and connect the live and neutral wires to the normally open contact (No. 87) and common contact (No. 30) of the relay, respectively. The relay coils (85, 86) are connected to the output terminal of the intelligent control module. When the air conditioner needs to be turned on, the intelligent control module powers on the relay coils to connect the air conditioner to the power supply and start working; When turning off the air conditioner, the coil loses power and the air conditioner stops running.
How to test 4-pin relays
1. Appearance inspection
Firstly, a visual inspection is required to check whether the relay housing is damaged or deformed, whether the pins are oxidized, and whether the pins are bent. Obvious defects in appearance can affect the performance and reliability of relays.
2. Electrical parameter measurement
Coil resistance measurement
Use a multimeter to measure the resistance between the two pins connected to the relay coil within the resistance range, typically terminal 85 and terminal 86. Then compare the measured values with the specifications given by the relay. If the deviation of the resistance value is too large, it may mean that the coil has been completely burned out or short circuited.
Contact resistance measurement
When the relay is not powered, set the multimeter range to resistance and measure the resistance between the two pins of the relay contacts (usually terminals 87 and 30) to obtain the normally closed contact resistance. Normally, normally closed contacts should have very low resistance, close to zero ohms.
Then, turn on the relay coil, open the relay, and measure the resistance of the normally open contacts. Normally open contacts, such as terminals 87 and 30 connected; Similarly, the resistance of normally open contacts must be as small as possible. If the contact resistance is too high, it may further increase the voltage drop of the circuit in practical use, thereby affecting the normal operation of the load.
3. Functional testing
Manual testing
DC power supply (such as 12V battery) and switch can be connected to each other. The positive pole of the power supply can be connected to one pin of the relay coil, such as terminal 85; Its negative pole can be connected to another pin of the coil through a switch (such as terminal 86).
Connect the load between relay contacts 87 and 30. For example, it can be a light bulb or a resistor.
Manually use the switch to power on/off the coil to check if the load is connected/disconnected accordingly. If the relay can control the opening/closing of the load normally, it means that it is at least working properly.
Automatic testing
These are tools that can be used for automatic testing of relays: signal generators and oscilloscopes. The signal generator can generate a specified frequency and amplitude of the control signal connected to the relay coil, and the oscilloscope is used to measure the output signal of the relay contact. It detects response time and operating frequency as some performance indicators to see if the relay meets the requirements.
4. Reliability testing
Temperature test
Place the relay separately at high and low temperatures for a period of time, such as 70 ℃ and -20 ℃, and then test its performance again.
Observe the working status of the relay at different temperatures to see if there is any performance degradation or malfunction. If the relay can operate normally within a certain specified temperature range, it means it has good temperature reliability.
Vibration test
Install the relay on the vibration table and conduct vibration tests of certain intensity and frequency.
Observe whether the working state of the relay is stable during the vibration process, and whether there are problems with poor contact and operational errors. Vibration testing can simulate the actual use of relays, provide them with a mechanical environment for vibration, and verify their mechanical reliability. Five times
Life test
Simulate the working status of relays and switches based on practical applications, and continue multiple times. Record the number of relay operations and fault cases to see if they meet the lifespan requirements. In this way, decisions can be made regarding the reliability and stability of long-term use of relays.
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