How Do I Choose the Best Electrical Relay?
The relay is an automatic control device whose output quantity will change suddenly when the input quantity (electricity, magnetism, sound, light, heat) reaches a certain value. Automotive relays are relays used in automobiles. These relays have large switching load power, high impact resistance and high vibration resistance. The power supply in automobiles is mostly 12V, and the coil voltage is mostly designed to 12V. Because it is battery-powered and the voltage is unstable; the environmental conditions are harsh, the suction voltage V 60% VH (rated working voltage); the coil overvoltage is allowed to reach 1.5VH. The power consumption of the coil is large, generally 1.6 ~ 2W, and the temperature rise is high. Environmental requirements are quite harsh: in the engine compartment, the ambient temperature range is -40 ° C to 125 ° C, and the ambient temperature range in other locations is -40 ° C to 85 ° C; the relays used in the engine compartment must be able to withstand sand, dust, water and salt , Oil damage; vibration and shock are quite harsh.
Automotive Relay
The relay is an automatic control device whose output quantity will change suddenly when the input quantity (electricity, magnetism, sound, light, heat) reaches a certain value. Automotive relays are relays used in automobiles. These relays have large switching load power, high impact resistance and high vibration resistance. The power supply in automobiles is mostly 12V, and the coil voltage is mostly designed to 12V. Since is
When a certain voltage or current is applied to the two ends of the electromagnetic relay coil, the magnetic flux generated by the coil passes through a magnetic circuit composed of the core, the yoke, the armature and the working air gap of the magnetic circuit. As a result, the normally closed contact of the contact is opened, and the normally open contact is closed; when the voltage or current across the coil is less than a certain value, when the mechanical reaction force is greater than the electromagnetic suction, the armature returns to the initial state, and the normally open contact is opened, The normally closed contact is closed.
Then, the automobile relay can be regarded as an assembly composed of a control circuit that works with a coil and a main circuit that works with a contact. In the control circuit of the relay, there is only a small working current. This is because the contact capacity of the operating switch is small, and it cannot be used to directly control a load with a large amount of electricity. It can only be controlled by the contact of the relay. On and off.
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 is only driven in the electronic control unit
Automotive relays consist of a magnetic circuit system, a contact system, and a recovery mechanism. The magnetic circuit system consists of iron core, yoke, armature, coil and other parts. The contact system consists of static reed, moving reed, contact base and other parts. The restoration mechanism is composed of a restoration spring or a tension spring. [1]
1. Installation direction If the installation direction is consistent with the direction of the relay's impact resistance, the performance of the relay can be fully exerted. It is recommended that the impact direction be perpendicular to the movement direction of the contacts and the armature, which can effectively improve the vibration and shock resistance performance of the normally closed contact in the non-excitation state. When installing, make the relay's contact axis parallel to the ground, which can prevent contact splash and carbon from falling on the contact surface and improve contact reliability. Multiple groups of relays should avoid small load contacts under large load contacts.
2. Short-distance installation When multiple relays are installed at a short distance, it will cause abnormal heat generation, and a 2mm pitch is generally recommended. Installing a polar or magnetic latching relay at a short distance will affect the operating voltage.
3. The relay should be installed in the shell. Do not remove the shell and install it first. In order to prevent loosening, damage and deformation, please use spring washers. The tightening torque should be within the range of 0.5 to 70 N · m.
4. The insertion strength of the plug-in relay is recommended to be 40 ~ 70N. [1]
7.Large size open relay
Its size is 35.5 * 25.5 * 21, and the sealed type is open, so it is called a large size open type relay. In addition, it differs in that two antennae are raised at both ends of its upper end surface. It has strong reliability and adapts to high and low temperature. It is more suitable for headlamps, blowers and demisters. The parameters of the A9 series are as follows:
General @Contact Data
Electrical Life @ rated load | 100K cycles, typical |
Mechanical Life | 10M cycles, typical |
Insulation Resistance | 100M min. @ 500VDC |
Dielectric Strength, Coil to Contact Contact to Contact | 750V rms min. @ Sea level 500V rms min. @ Sea level |
Shock Resistance | 100m / s2 for 11 ms |
Vibration Resistance | 1.27mm double amplitude 10 ~ 40Hz |
Terminal (Copper Alloy) Strength | 8N |
Operating Temperature | -40oC to + 85oC |
Storage Temperature | -40oC to + 155oC |
Solderability | 260oC for 5 s |
Weight | 32g |
Contact Rating | 40A @ 14VDC NO |
Contact Resistance | <50 milliohms initial |
Switching Power MAX | 560W |
Switching Voltage MAX | 75VDC |
Switching Current MAX | 40A |
Coil Power | 1.8W |
8.Small power plastic sealed relay
The maximum switching power of its contacts is only 150W, and it adopts plastic encapsulation, which belongs to a low-power plastic encapsulation relay. Although its maximum switching voltage and current are relatively small. It is characterized by strong erosion resistance, low consumption, and is widely used in circuit modules of the starting system. The parameters of the A15 series are as follows:
A151AS12VDC
General @Contact Data
Electrical Life @ rated load | 100K cycles, typical |
Mechanical Life | 10M cycles, typical |
Insulation Resistance | 100M min. @ 500VDC |
Dielectric Strength, Coil to Contact Contact to Contact | 500V rms min. @ Sea level 500V rms min. @ Sea level |
Shock Resistance | 100m / s2 for 11 ms |
Vibration Resistance | 1.27mm double amplitude 10 ~ 40Hz |
Terminal (Copper Alloy) Strength | 10N (quick connect), 4N (PCB pins) |
Operating Temperature | -40oC to + 85oC |
Storage Temperature | -40oC to + 155oC |
Solderability | 260oC for 5 s |
Weight | 5.5g, 11g |
Contact Rating | 10A @ 14VDC |
Contact Resistance | <50 milliohms initial |
Switching Power MAX | 150W |
Switching Voltage MAX | 20VDC |
Switching Current MAX | 30A |
Coil Power | 0.7W |
In the selection of automotive relays, analysis and research can be carried out item by item according to the following points: appearance and installation method; input parameters; output parameters; environmental conditions; electromagnetic compatibility; installation and use requirements.
First, the attention of the coil input
1. The rated voltage is a guarantee of the reliability of the relay. Although the relay can work when the coil voltage exceeds the operating voltage, it will erroneously operate the coil voltage under the strong impact. The maximum operating voltage will cause the coil insulation to drop, turn-to-turn short circuit, and burnout.
2. The coil resistance value of the relay will cause a change of about 0.4% due to changes in the ambient temperature and the heating of the relay itself. Therefore, if the coil temperature increases, the operating voltage and the off voltage will also increase.
3. The automobile relay is driven by a battery. As a large load is turned on, the power supply voltage will be reduced, which will affect the life of the relay. Pay attention to the influence of power supply voltage fluctuations on the reliability of the relay.
4. Maximum continuous applied voltage of the coil: In addition to the stability of the relay, the maximum continuous applied voltage of the coil is mainly limited by the insulation performance of the enameled wire. The insulation level of the product's enameled wire should be understood. In actual use, when the ambient temperature is 40 ° C, the temperature rise limit can be considered to be 115 ° C, which is determined by the resistance method. However, due to the unevenness of the inner and outer rings, the recommended value is 105 ° C.
5. Coil electrical corrosion: Automotive relays work in a temperature and humidity cycle environment for a long time. When the coil is continuously connected to the positive pole of the power supply (disconnect the negative pole), the coil will be electrically corroded and cause disconnection, so the relay coil cannot be connected to high potential It must be ensured that the relay coil and moving reed are disconnected from the positive pole of the power supply.
Second, the use of contact points
The contact is the most important part of the relay. The working reliability of the contact is affected by the contact material, contact voltage and current (especially the on and off voltage, current waveform), load type, on-off ratio, and environmental conditions. . Contact voltage: Inductive load will generate a very high reverse voltage. The higher the voltage, the greater the energy, which accelerates the contact's electrical corrosion and metal transfer. It should be noted. Contact current: The current when the contact is closed and opened has a great influence on the contact. When the load is a motor or a headlight, the inrush current when closed is large, the contact loss and the amount of metal transfer are greater, and the contact transfer may cause contact bonding failure. A confirmation test should be performed. 1. Contact protection reverse voltage: When disconnecting the relay coil series circuit or inductive loads such as motors and electromagnets, surge absorption must be adopted to protect the contacts. When the inductive load is disconnected, a reverse voltage of hundreds to thousands of V will be generated, which will increase the electrical corrosion of the contacts and reduce the life. In addition, when the inductive load current is less than 1A, the arc generated by the reverse voltage decomposes the organic gas volatile from the coil and plastic in the relay, generating ochre-colored acid compounds and carbides on the contacts, causing poor contact. Contact metal transfer: Contact metal transfer is the transfer of contact material in one direction under the action of direct current. With the increase of the number of on and off times, the anode contact generates a pit, and the cathode contact generates a bulge. It is easy to produce mechanical self-locking with pits and cause contact sticking. Use transfer-resistant contact materials or protective circuits. Contact protection absorption circuit: The use of contact protection elements or protection circuits can reduce the reverse voltage, but if it is not used correctly, it will have a negative effect.
Third, the use of relays
1. In order to prevent the surface of the lead-out terminal from being contaminated, the lead-out terminal should not be directly contacted, otherwise the solderability may be reduced.
2.The position of the terminal should be
It is consistent with the hole position of the printed board. Any improper cooperation may cause the relay to generate dangerous stress, which will damage its performance and reliability.
3. After the relay is inserted into the circuit board, do not bend the lead-out pin to avoid affecting the relay seal or other performance.
4. Do not apply excessive pressure to the relay case during the insertion process, so as not to rupture the case or change the operating characteristics.
5. The insertion and extraction pressure of the quick connection foot is 10 kgf. Too much insertion force will cause damage to the relay, and too little pressure will affect contact reliability and current carrying capacity.
6. It is particularly emphasized that if the relay is accidentally dropped or impacted during installation, although the electrical parameters are qualified, the mechanical parameters may change greatly. There are serious hidden dangers and should be avoided as much as possible.
7. Do not use silicon-containing resins and preservatives, which will cause contact failure, even plastic-sealed relays.
8. Pay attention to connect the coil power and contact power according to the specified polarity. The contact is usually the positive (+) of the moving spring.
9. Avoid the voltage applied to the coil exceeding the maximum allowable voltage or the temperature rise of the coil exceeding the insulation level of the enameled wire.
10. The rated load and life are under the prescribed standard conditions, and it is impossible to cover the various requirements for use of automotive relays.
The load and life of the actual application contact will be significantly different due to the load type, environmental conditions, operating frequency or other various conditions. Please perform a test or contact the relay manufacturer for technical support. [1]
