Guidelines for selecting automotive relays
Car relays are relays used in cars. Qualified automotive relays are the first line of defense for road safety, so automotive relays are more stringent than other relays from production to testing. Today, I will show you the relevant knowledge of choosing automotive relays.
The application position of automotive relays in automobiles
We hardly have the chance to see car relays, but many functions of cars cannot be achieved without the contribution of car relays. For example, the lights, wipers, starters, air conditioning units, electric seats, electric doors and windows, anti lock braking devices, suspension controls, audio and other controls of a car all require the use of relays. On average, a car needs to use 10-20 relays.
Selection Guide for Automotive Relay - Environmental Parameter Considerations
1. Temperature
The temperature difference between different positions in a car is significant, and the performance of the relays used will also vary significantly. Precautions at different temperatures:
1) At high temperatures, insulation materials are prone to softening and melting, while at low temperatures, materials are prone to cracking and insulation resistance decreases. So when choosing a car relay, one should consider the temperature difference in different parts and make a reasonable choice.
2) The application areas with large temperature differences are prone to loosening the relay structure, changing the position of moving parts, causing uncontrolled suction and release, and poor or no contact of contacts.
3) Under high temperature conditions, the coil resistance increases and the suction voltage correspondingly increases, resulting in loose suction and relay failure. In addition, at high temperatures, when switching power loads on contacts, the arc breaking ability decreases, contact corrosion and metal transfer intensify, the likelihood of failure increases, and the lifespan shortens.
2. Damp heat
It is easy to cause relay failures in humid and hot environments:
1) Long term humidity and heat will directly lead to a decrease in insulation resistance level, resulting in complete failure. Especially for relays that have been contaminated by sand and dust for a long time and are subjected to moisture and heat, insulation failure will occur.
2) Under humid and hot conditions, the coil of a non sealed relay may break due to electrochemical corrosion or mold, and the electrochemical corrosion and oxidation of the contacts may intensify; The corrosion rate of metal parts has significantly increased, resulting in complete failure.
3) Under humid and hot conditions, when the contact is charged to switch loads, the arcing phenomenon intensifies, leading to a shortened electrical life. Electronic products used in tropical and subtropical regions must fully consider moisture and heat issues in product design and material selection.
3. Sand dust
During high-speed driving, cars may suffer from severe sand and dust pollution, leading to inflexible rotation (sliding) of moving parts and electrical contact failure of contacts; Under the influence of moisture, corrosion of metal parts intensifies, and the insulation performance of insulation parts decreases, leading to failure.
4. Chemical atmosphere pollution
When a car encounters chemical atmosphere pollution such as sulfur dioxide and salt spray in the working environment, it can cause corrosion to the contacts, metal parts, coils, insulation parts, etc. of the relay, leading to poor electrical contact of the contacts and failure; Causing corrosion and breakage of coil leads, as well as a decrease in insulation level.
5. Mechanical vibration
During the process of car formation, internal motors and other vibrations, as well as external bumpy road sections, may cause loosening, fatigue, and noise in the mechanical components of the relay, which can seriously lead to the fracture and failure of the relay components.
6. Mechanical impact
During the transportation and handling process of automobiles, mechanical impact is inevitable. Impact can cause the relay structure to loosen, damage, break, and lose its working ability. When receiving an impact, the closed contact produces an instantaneous disconnection greater than the specified requirement and fails; Breaking the contact produces an instantaneous closure greater than the specified requirement and fails.
So when choosing a car relay, having a certain level of impact resistance is essential.
Selection Guide for Automotive Relay - Safety Parameter Selection
1. Insulation material: The insulation material used in automotive relays should have good temperature resistance, and the long-term operating temperature should reach 125 ℃.
2. Insulation withstand voltage level: The relay withstand voltage we often refer to refers to the withstand voltage between contacts, insulation resistance, and the withstand voltage and insulation resistance between contact coils. The typical values of automotive relays are withstand voltage of 500 VAC and insulation resistance of 100 M Ω.
3. Electromagnetic compatibility: Electromagnetic compatibility is divided into electromagnetic interference (EMI) and electromagnetic anti-interference (EMS). Plug in automotive relays typically have parallel resistors or diodes for transient suppression, causing the coil back electromotive force to be less than 100V. When the relay contacts break, an arc is generated, emitting electromagnetic waves that affect the operation of the IC. If this situation occurs, an arc extinguishing circuit can be added to the contacts. It is also possible to increase the distance between the relay and IC appropriately.
