Auto Electrical Works Paper 2, WASSCE (SC), 2021

Question 2

 

  1. With the aid of a sketch, explain the principle of operation of a starter motor.
  2. State three factors that affect the efficiency of a starter motor.

 

Observation

 

The expected responses were:

 

Sketch showing the principle of operation of a starter motor

How Starting System, Starter Motor, and Starter Drive Works?

 

In a starter motor, electric current is passed through field and armature coil which creates a magnetic field in both coils. The magnetic fields created oppose each other since the field coil is fixed, the armature rotates. The rotating armature is connected to a spindle. As the armature rotates the spindle, the spindle rotates the pinion which in turn rotates the flywheel. The rotation of the flywheel cranks the engine.


  • Factors that affect the efficiency of a starter motor
  • Current at a given load
  • Number of turns in the starter fixed coil
  • Number of turns in the armature moving coil
  • Strength of the magnets
  • Rotating speed of armature winding
  • Gear ratio of flywheel to pinion
  • Battery capacity/voltage

 

Question 2 basically required candidates show good understanding of the principle of operation of a starter motor. The report by the Chief Examiner indicated that majority of the candidates could not respond well to tasks especially the first.