Working of Starter Motor: 

a. Starter motor armature has many coils fitted on the armature. As principle of starting motor that when a current carrying conductor is placed inside a strong magnetic field, the conductor experiences repulsive force. But starter motor has many conductors on its armature, so the armature is force to rotate between pole shoes with powerful torque to start engine. When the starter switch is ‘ON’, current from storage battery flows to the starter motor. It sets up a strong magnetic field around the armature coils. The armature coils act as current carrying conductors. The same current from battery also flows through the field windings (or field coils) around pole shoes.

b. This makes pole shoes as electromagnets due to which a strong magnetic field is created between pole-shoes. So, the reaction of two magnetic fields (i.e., armature windings & field windings) tends to be distorted or bent the magnetic lines of force of field magnet. Due to distortion of magnetic field the force is exerted on the armature coil, causing the armature to rotate between pole shoes.

This torque of starter motor is utilized to crank engine through drive mechanism. Torque exerted by starter motor will be proportional to the amount of current fl owing in field coils and armature coils.