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What are the precautions for using automotive relays?


1. Precautions for coil input

1. The rated voltage is the guarantee of the working reliability of the relay. Although the relay can work when the coil voltage exceeds the operating voltage, it will malfunction under strong impact.

2. The coil resistance value of the relay will change by about 0.4% ℃ due to the change of the ambient temperature and the heat of the relay itself. Therefore, if the coil temperature rises, the operating voltage and disconnection voltage will also increase.

3. The automotive relay is driven by a battery. When a heavy load is connected, the power supply voltage will decrease, 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. The 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. You should know the insulation level of the enameled wire of the product. In actual use, when the ambient temperature of Class F insulation is 40°C, it can be considered that the temperature rise is limited to a maximum of 115°C measured by the resistance method. However, due to the unevenness of the inner and outer rings, the recommended value is 105°C.

5. Coil electric corrosion: Automobile relays work for a long time in an environment of temperature and humidity cycles. When the coil is continuously connected to the positive pole of the power supply (disconnecting the negative pole), the coil will be galvanically corroded and cause disconnection, so the relay coil cannot be connected to a high potential. It must be ensured that the relay coil, moving reed and the positive pole of the power supply are disconnected.

2. Matters needing attention in the use of automotive relay contacts

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 loads will generate very high reverse voltages. The higher the voltage, the greater the energy, which will accelerate the electrical corrosion and metal transfer of the contacts, so attention should be paid. 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 closing is large, the loss of the contact and the amount of metal transfer will be greater, and the transfer of the contact will cause contact bonding failure, and a confirmation test should be carried out.

1. Contact protection against reverse voltage: When disconnecting relay coil series circuits or inductive loads such as motors and electromagnets, surge absorption such as diodes must be used to protect contacts. When the inductive load is disconnected, a reverse voltage of hundreds to thousands of V will be generated, which will aggravate the electrical corrosion of the contacts and reduce the service life. In addition, when the inductive load current is less than 1A, the arc generated by the reverse voltage will decompose the organic gas volatilized in the inner coil of the relay and the plastic, and generate black acidification and carbonization on the contacts, resulting in poor contact. Contact metal transfer: Contact metal transfer is the transfer of contact materials in one direction under the action of direct current. With the increase of the number of on-offs, the anode contacts produce pits, and the cathode contacts produce bulges. And pits are easy to produce mechanical self-locking and cause contact adhesion. Transfer-resistant contact materials or protective circuits should be selected. Contact protection absorption circuit: Using contact protection components or protection circuits can reduce the reverse voltage, but if it is not used correctly, it will have a negative effect.


3. Matters needing attention in the use of automotive relays

1. In order to prevent surface contamination of the terminal, the terminal should not be directly contacted, otherwise, the solderability may be reduced.

2. It matches the hole position of the printed board. Any improper fit may cause dangerous stress to the relay and impair its performance and reliability. Please refer to the punching diagram in the catalog to drill holes.

3. After the automotive relay is inserted into the circuit board, the lead-out pins must not be bent, so as not to affect the sealing or other performance of the relay.

4. Do not exert excessive pressure on the relay casing during the insertion process, so as to avoid the casing cracking or the change of operating characteristics.

5. The insertion and extraction pressure of the quick-connect pin is 10 kg force. Too much insertion force will cause damage to the relay, too little pressure will affect the 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, its mechanical parameters may change greatly, and there are serious hidden dangers, so it should not be used as much as possible.

7. Do not use silicon-containing resin and preservative, which will cause contact failure, even for plastic-sealed relays.

8. Pay attention to connect the coil power supply and contact power supply according to the specified polarity. The contact is generally connected to the positive pole (+) by 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 specified standard conditions, and it is impossible to cover various use requirements of automotive relays.

The load and life of the actual application contacts will be significantly different due to the type of load, environmental conditions, operating frequency or other conditions. Please conduct a test test or contact the automotive relay manufacturer for technical support.