How automotive relays work

When a certain voltage or current is applied to both ends of the electromagnetic relay coil, the magnetic flux generated by the coil passes through the magnetic circuit composed of the iron core, yoke, armature, and working air gap of the magnetic circuit

Under the action of the magnetic field, the armature is attracted to the pole face of the iron core, thereby pushing the normally closed contact to open and normally open contact to close; When the voltage or current at both ends of the coil is less than a certain value, and the mechanical reaction force is greater than the electromagnetic attraction, the armature returns to the initial state, the normally open contact is disconnected, and the normally closed contact is connected.

Then, the automotive relay can be regarded as an assembly composed of two parts: the control circuit of the coil and the main circuit of the contact.

In the control circuit of the relay, there is only a small working current. This is because the contact capacity of the control switch is small, and it cannot be used to directly control the load with a large power consumption. It can only be controlled by the contact of the relay on and off.