The working principle and function of automobile relay

Relay is an automatic control device that changes the output by leaps and bounds when the input quantity (electricity, magnetism, sound, light, heat) reaches a certain value. The automobile relay is the relay used in the automobile, which has large switching load power, high impact resistance and high vibration resistance. The power supply in the car uses 12V, and the coil voltage is mostly designed for 12V. Because it is a battery power supply, the voltage is unstable, and the environmental conditions are harsh, the suction voltage V≤60%VH (rated operating voltage), and the coil overvoltage is allowed to reach 1.5VH. The coil power consumption is large, generally 1.6 ~ 2W, and the temperature rise is high. The environmental requirements are quite harsh: in the engine room, the ambient temperature range is -40 ° C ~ 125 ° C, and the ambient temperature range in other locations is -40 ° C ~ 85 ° C, and the relays used in the engine room should be able to withstand the damage of sand, water, salt and oil.

(1) Automotive relay

1. What is a car relay
1.1 Definitions
In the simplest terms, we can say that a relay is a switch, which is the same switch that turns on and off fans and light bulbs on the walls of your home. The two switches are the same, they both make and break the circuit. But they have one difference, that is, the homing switch is manually operated, while in the car it is electrically operated.
Automotive relays are composed of magnetic circuit system, contact system and recovery mechanism. The magnetic circuit system is composed of iron core, yoke iron, armature, coil and other parts. The contact system is composed of static reed, moving reed, contact base and other parts. The restoring mechanism consists of a restoring reed or a tension spring. Therefore, automotive relays are also called electric switches or electromagnetic switches.
There is a large market for automotive relays. The demand for safety, luxury and comfort in automobiles has made the automotive relay market increasingly large.　

1.2 Automotive relay housing Marking
Car relay housing identification:
Voltage: Relays are marked with 6, 12 and 24 volts.
Current: The relay is marked with a rated current of 30/40 amps. This current rating is suitable for high amperage circuits.
Relay terminals: Numbers 85, 86, 30, 87 and 87a are marked on the plastic housing of the relay along with the circuit schematic.

(2)Automotive relay housing and marking

2. Automotive relay wiring diagram
According to the DIN72552 standard, each pin of the relay is numbered 85, 86, 30, 87 and 87a. The relay has two circuits, a coil circuit and a high current circuit. In relays, pins 85 and 86 are considered coil circuit pins, while pins 30, 87, and 87a are considered high current circuits. Generally, terminal -85 is the ground power supply and terminal +86 is the hot power supply to form a complete circuit.

Terminal 30 is considered a common terminal. The 12-volt power supply is connected to the relay (we can say the power cord) through this terminal. The second wire of the high amperage circuit terminal 87 takes power from the relay and sends it to the assembly. There is a third wire in the high current circuit of the 5-pin relay, called terminal 87a. It is an additional fifth terminal and is not commonly used in automotive relays. It is used in circuits that require power when the relay is not activated.

(3)Automotive relay wiring diagram

2.1 Four-pin relay wiring diagram
In a four-pin relay, there are four terminals, two terminals for the coil circuit and two terminals for the high-current circuit. The two terminals of the coil circuit are 85 and 86 respectively. The 85 terminal is the negative contact of the relay coil, and the 86 terminal is the positive contact of the relay coil. Similarly, the two terminals of the relay's high-current circuit are 30 and 87, of which 30 terminal is the common contact, that is, the input contact, and the current entering the relay through the terminal is positive or negative depending on the energy source required by the relay. Terminal 87 is a normally open contact, and the relay is closed when powered on. It is also called the output terminal, meaning that the current comes out of the relay and reaches the component through this terminal.

(4)  Four Pins  Automotive relay 

2.2 Five-pin relay wiring diagram
The five-pin relay has five terminals, of which two terminals are used for coil circuits and three terminals are used for high-current circuits. The two wires of the coil circuit are terminals 85 and 86, where terminal 85 is regarded as a negative contact and terminal 86 as a positive contact. The high-current circuit of a five-pin relay consists of three terminals 30, 87, and 87a. Terminal 30 is a common contact through which battery power reaches the battery. Terminal 87 is a break contact that remains open at all times and closes when the relay is energized. When the relay is energized, power is output to the assembly through this terminal. Similarly, the terminal 87a is a normally closed contact that opens when the relay is energized. This means that, by default, it discharges the current without energizing the relay and stops the current when the relay is energized. It is used in applications where current is required when the relay is not powered on.

(5) 5 pins automotive relay

3. Working principle of automobile relay
The working principle of automotive relays is electromagnetic. When a current flows through the relay, it creates an electromagnetic field to attract the movable rod for connection.
When a certain voltage or current is added to both ends of the solenoid relay coil, the magnetic flux generated by the coil passes through the magnetic circuit composed of the iron core, yoke iron, armature and the working air gap of the magnetic circuit. Under the action of the magnetic field, the armature attracts to the pole surface of the iron core, thus pushing the normally closed contact to break and the normally open contact to close. When the voltage or current at both ends of the coil is less than a certain value, when the mechanical reaction is greater than the electromagnetic suction, the armature returns to the initial state, the normally open contact is disconnected, and the normally closed contact is connected.
Then, the automobile relay can be regarded as a collection of two parts: the control circuit of the coil work and the main circuit of the contact work. In the control circuit of the relay, there is only a small working current, which is because the contact capacity of the control switch is small, which can not be used to directly control the load with large power consumption, and it can only be controlled through the contact of the relay.
The relay is both a control switch and a control object (actuator). Take the fuel pump relay as an example, it is the control switch of the fuel pump, but the coil of the fuel pump relay can only form a loop through the ground point of the electronic control unit when the transistor is driven on in the electronic control unit.
According to Faraday's law, any change in a magnetic field creates an electromotive force (electricity), while any change in an electric current in a conductor creates a magnetic field around that conductor. When the current flows through the coil circuit of the relay, an electromagnetic field is generated that attracts the high current circuit of the movable rod connected to the relay.
4. Function of automobile relay
According to the needs of the work, automotive relays have many different uses, the following is the use and function of automotive relays.
4.1 Component Reliability
The purpose of relays is to improve the efficiency of components by providing the right amount of current, and relays support the components to operate at the highest level of performance.
4.2 Reduce the voltage drop
The purpose of relays is to increase the efficiency of components by providing the right amount of current. Relays also enable components to operate at the highest level of performance.
4.3 Control multiple circuits with a single relay
The function of relays is also to control multiple circuits with one relay. A single relay trigger will activate one or more higher current circuits. These circuits perform multiple functions simultaneously without having to use a bunch of relays and wires. A good example is a car control lock system: a trigger causes all door locks to lock or unlock at the same time.

4.4 Handling high-current circuits
One use of relays is to handle high current loads by using low current loads. Some accessories require too much current, exceeding the capacity of the wire, causing the wire to burn. The coil circuit of the relay uses a current of almost 0.5 amps. In this case, if a relay is used, the circuit will be protected from line overload or overloading. In addition, another benefit of using relays is that high current rated cables are not required. This also reduces cost and weight. For example, high output headlights require a lot of current, which can overload the wire capacity. By using relays, we switch high current circuits with low current circuits. Normal relays can handle currents up to 40 amps.4.5 Provide circuitry for suitable fuses
Another benefit of using relays is that it allows you to use separate and suitable fuses for each circuit.
4.6 Performing Logical Functions
One of the functions of relays is to perform logic functions. Relays are used for instantaneous inputs, time-base functions, and replacement work (such as flushing replacement left or right lights).

5. Common problems of automotive relays
5.1 What is the car relay used for?
A relay is a switch controlled by a power source, such as another switch, a computer, or a control module. Automotive relays are designed to automatically open and close circuits at specific times.
5.2 How much is the car relay switch?
Starting relays cost about $20 to $80, while main relays cost about $20 to $200. In order to determine the type of vehicle relay you need to replace, it is important to consult the vehicle's owner's manual before purchasing replacement parts.
5.3 Are automotive relays universal?
Not all relays are the same. Although it has the same number and location of terminals, it does not mean that the relay is suitable for the application. Some relays, when used in the wrong applications, can produce voltage spikes in excess of 100V on traditional 12V systems.
5.4 How do I determine if the car relay is broken?
If you feel and hear a click, the relay works on the side with the circuit and coil. However, if the speaker does not sound, there is a problem with the contact circuit of the relay.
5.5 What happens if the car relay is broken?
If there is a problem with the ignition relay in the car, it will encounter a sudden shutdown. This happens because the spark is cut off and no longer able to sustain combustion because the relay can no longer keep the current flowing to the car's spark plug.
The above is the introduction of the working principle and function of the automobile relay. Note The relay should be stored and installed in a clean environment, please use a dust cover or plastic seal relay in the presence of dust pollution environment. Should also pay attention to monitoring the storage temperature, try to avoid the relay storage time is too long. During the transportation process, if a large drop impact is applied to the relay, it may cause dysfunction. Please pay attention to whether the appearance of the packaging material is complete. Relay using long tube packaging, when the number of relays is small, if the lack of limit, will slip and affect the appearance and characteristics of the relay, special attention should be paid.