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

Question 4

 

(a) The following are parts of an alternator which was dismantled by a technician.

Rectifier                roller bearing               rotor                Regulator        Stator
Protective cap       Drive-end shield         Pulley              Slip ring          End shield

(i)         Arrange these parts in the correct order of assembling from the pully to the protective cap.
1:         Pulley                                      6:         _____________________
2:         ______________________    7:         _____________________
3:         ______________________    8:         _____________________
4:         ______________________    9:         _____________________
5:         ______________________    10:       Protective cap

            (ii)        State the function of the rectifier in the alternator.

(b)        Fig. 2 is a graphical representation of the result obtained when charging a battery.


Use the graph to estimate the:
(i)         time required for the battery to be fully charged;
(ii)        voltage at the maximum charge;
(iii)       voltage at 45 minutes;
(iv)       time-rate of charging.

 

Observation

      The expected responses were:
           

  • (i)         Order of assembling parts of an alternator

1 – pulley
2 – drive-end shield
3 – roller bearing
4 – rotor
5 – slip ring
6 – stator
7 – end shield
8 – regulator
9 – rectifier
10 – protective cap

(ii)        Function of rectifier in an alternator

  • Converts alternating current to direct current/pulsating signal
  • (i)         60 minutes – 70 minutes                                            

(ii)        12.6 V – 13.0 V          
(iii)       7.0 V – 9.0 V  
     

      

Question 4 required candidates to show understanding of how parts of an alternator are assembled and make deductions from a graph illustrating the charging of a battery. It was reported that majority of the candidates that attempted question 4 could not give the correct order of arrangement of the alternator parts. However, many were able to read off from the graph given in the second task.