The construction of the STARTER MOTOR is similar to that of the generator, but the winding brush terminals are heavier to deal with heavy currents. The brushes are made of low-resistance material, such as copper, instead of carbon, as in the generator case.

The main parts of the starting motor are the casing, armature, commutator, field winding brushes, poles, and terminals. The motor starts the engine using a drive mechanism that is located at the end of the armature shaft.

The starting motor use either two-field windings or four-field windings. Above figure shows a motor using two field windings. The current from the battery divides when it enters the motors, each branch leading to the separate field winding.

Current is led to the armature’s commutator from the fields through the two insulated brushes. The current in the armature simultaneously creates four poles adjacent to the four field poles to produce the attractive and repulsive forces that turn the armature.

The armature current is returned to the battery via the two grounded brushes. Above figure shows a starting motor with four field windings. It is used in large engines to develop more torque. It functions in a similar way to the two-winding type.