Automotive Electronics Practice Test

The primary purpose of the commutator in a starter motor is to?

1. Convert AC to DC

2. Switch the magnetic field

3. Collect generated current

4. Control engine speed

The correct answer is: Convert AC to DC

The primary purpose of the commutator in a starter motor is to convert alternating current (AC) to direct current (DC). Although starter motors are typically powered by a DC supply from the vehicle's battery, the commutator plays a crucial role in ensuring that the electric current flowing through the motor's windings maintains the correct direction for efficient motor operation. In a starter motor, the armature (rotor) rotates within a magnetic field created by field coils or permanent magnets. As the armature turns, the direction of the induced current in the windings changes due to the nature of electromagnetic induction, which could lead to an ineffective motor operation if left uncorrected. The commutator rectifies this induced AC into a unidirectional current, ensuring that the motor's torque is always in the same direction for consistent and reliable cranking of the engine. The design and function of the commutator are integral to the operation of many electric machines, making its role essential to the reliability of starter motors in automotive applications.