Selection of main relay
● The load carried by the main relay is: front and rear oxygen sensor 10A, fuel injector 4A, ignition coil 10A, carbon tube solenoid valve 1A, the nominal voltage is 12V, all are inductive loads, and the peak current should be considered.
● The vehicle uses 12V DC power supply, the rated voltage of the coil provided by the control circuit is 12V, and the rated voltage of the relay coil should be selected to be above 12V/DC.
● The position of the main relay is set in the power distribution box of the cab, and the relay with an ambient temperature of -40 to 85°C can be selected.
● The coil end of the main relay is powered by the battery, so that the contact end outputs the power signal to each load, and selects a normally open four-pin relay with one contact.
● The sum of the rated current of the calculated load is about 25 A. According to the principle that the switching load of the relay is less than 70% of the rated current, considering that the ECU is a continuous working load, the relay with a rated current greater than 40 A can be used.