Question 2
- With the aid of a sketch, explain the principle of operation of a starter motor.
- 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
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.