PCB board type non-plastic encapsulated relays are highly susceptible to contamination by flux, it is recommended to use flux-resistant or plastic-encapsulated relays to prevent flux gas from invading from the terminal and the gap between the base and the shell. minutes), it can further prevent flux intrusion.
2. Welding process
When fluxing or automatic soldering is used, care should be taken not to damage the relay performance, flux-resistant relays or plastic encapsulated relays may be suitable for dip or wave soldering processes, but the maximum soldering temperature and time should be controlled depending on the relay selected.
1. Wave soldering: The recommended soldering temperature is: 240℃～260℃, the time is about 5 seconds, and the best soldering temperature is 250℃. For other soldering temperature and soldering time (such as higher solder temperature, the soldering time will be shortened accordingly), please contact our technical service support or confirm the soldering quality.
2. Manual welding: The recommended welding temperature is 300℃-350℃, and the welding time is controlled within 2 seconds.
3. Cooling: The heating of the relay caused by the soldering process can be alleviated by cooling at the end of the process, so do not change the temperature suddenly, especially avoid cold shock to the thermal relay.
Soldering with no-clean flux should be used whenever possible, and overall cleaning of the relay should be avoided. Prevent cleaning agent from entering the relay and causing it to fail. Ultrasonic cleaning is prohibited to avoid contact cold welding, enameled wire breakage and other structural damage caused by ultrasonic energy. Immediately after cleaning and drying, ventilation should be performed to bring the relay to room temperature.
Sometimes in order to ensure the moisture resistance and high insulation of the circuit board, the circuit board must be coated with a preservative, and a softer glue that does not contain silicon should be used. The coating process should prevent the relay from generating negative pressure and inhaling the preservative.
(1) Simple method for judging the working performance of the relay
Turn on the ignition switch, and then use your ear or stethoscope to listen to the sound of the control relay, or feel the vibration of the relay with your hand. ; otherwise, it means that the relay is not working properly.
You can also unplug the relay for testing, for example, if the air conditioner compressor does not work, you can start the engine, and then turn on the blower switch and the air conditioner switch. Then unplug the connector of the air conditioner compressor relay to judge. If the sound of the relay action can be heard, and the engine speed drops significantly when the relay is unplugged, and the engine speed rises when the relay is inserted, it means that the air conditioner compressor relay and its control circuit are normal.
Regarding the position of the relay, all relays and fuses marked with a dotted line on the circuit schematic diagram are generally arranged in the central distribution box.
(2) Common failures of relays Common failure phenomena of relays include: coil burnout, inter-turn short circuit (insulation aging), contact ablation, thermal decay, and inability to adjust the initial operating current.
①The relay coil is burnt out. In order to prevent this from happening, if the temperature may exceed 80°C during repair, maintenance and electric welding, the temperature-sensitive relays and electronic control units should be removed.
② Contact ablation. For example, the relay of the condenser fan of the Jinbei Hiace car air conditioner is just below the glass cleaning water spray pipe. If the water spray pipe is broken, the cleaning liquid will leak to the relay, so that the normally open contact of the relay is corroded and cannot be disconnected. , it will cause the failure of the air conditioner condenser fan to keep running. Therefore, water should be strictly prevented from entering the relay.
(3) Try to reduce the contact resistance of the relay contacts
The contact resistance existing between the contacts of the automotive relay is mainly composed of two parts: shrinkage resistance and surface film resistance. The contact resistance of the contact is related to the contact form, material properties and surface processing of the contact. It can be seen that to reduce the contact resistance of the relay contacts, under the condition of a certain contact pressure, it can be started by improving the contact state and improving the contact material.
(4) The poor grounding of the ECU may affect the normal operation of the relay. When a car is driving normally, the engine automatically shuts down and starts again, and the car cannot be driven. Turn on the ignition switch, no sound of the fuel pump running, and no high pressure fire. Check the ignition coil and find that there is no power supply on the plug, but the resistances on the primary and secondary sides are normal. Measure the car's jetted double-sealed relay, which has a 12V power supply at its plug. Replaced the spray double-sealed relay, but there is still no high-voltage fire, and there is no sound of the relay pulling in. Use a wire to directly ground the 10th pin of the jet double-sealed relay, you can hear the sound of the relay being pulled in, and the engine has been started successfully. But the strange thing is that after disconnecting this ground wire, the engine does not turn off, and after turning off the ignition switch and restarting the engine, it is normal. Analysis of the reasons, this is due to the poor grounding of the engine ECU, resulting in a very low power supply voltage of the relay coil (sometimes only about 2V), and it is impossible to make the relay pull in. After the wire is directly grounded, the relay has a voltage of 12V, so it is smoothly pulled in, so the engine starts successfully. After the temporary ground wire is removed (the ignition switch is still on), the relay still has a low holding voltage (this is a common feature of relays), even if this holding voltage is only 2V, the relay will not break on, so the engine doesn't turn off. When the ignition switch is turned off, the self-induced electromotive force generated by the circuit is much higher than the power supply voltage. Under the action of this strong electromotive force, the grounding place with poor contact may return to normal, so the engine is normal after starting. However, the above faults will recur, so the way to eradicate it is to thoroughly deal with the bad grounding.