Starter motors and alternators

Starter motors and alternators

Starter Motors

  • A starter motor is a high-torque electric motor designed to draw enough current to start an internal combustion engine.
  • An internal combustion engine cannot start on its own. A starter motor initiates the process by turning over the engine to suck in and compress air. A spark can then ignite the fuel-air mix to start the engine.
  • The starter motor is directly connected to the battery of a vehicle via a heavy-duty cable.
  • When you turn the ignition key, it completes a circuit that carries electricity from the battery to the starter motor. This fires up the starter motor’s high-strength electric motor.
  • Once the engine starts, a built-in solenoid automatically disengages the starter motor to prevent damage.
  • Problems with the starter motor can prevent the vehicle from starting, or cause inefficient starting (slow turning or abnormal noise).


  • An alternator generates electricity to meet the vehicle needs after the car has started, and to rejuvenate a depleted battery.
  • The alternator is mechanically driven by the engine via a belt, it converts mechanical energy to electrical energy.
  • The power from the alternator is directed firstly to the necessary systems of the car, and any excess is directed to the battery.
  • It produces Alternating Current (AC), which is converted into Direct Current (DC) by the diode rectifier block before it reaches the battery and other electrical systems.
  • The amount of electricity produced by the alternator is regulated based on the battery’s state and the vehicle’s electrical needs.
  • A malfunctioning alternator can result in a flat battery, dimmed lights, difficulty starting, or even a breakdown.

Interaction of Starter Motors and Alternators

  • The starter motor and the alternator work in a cycle in order to start the vehicle and maintain its electrical power.
  • Initially, the battery powers the starter motor to turn over the engine, this causes the starting of the vehicle.
  • Once the engine is running, it powers the alternator. The alternator’s primary function is to maintain the battery’s charge and power the electrical system.
  • If either of these components fails, it can create a range of electrical problems that can disable the vehicle.