Observation

The expected responses were:

Sketch showing the principle of operation of a starter motor

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.