Auto Electrical Works Paper 2, WASSCE (SC), 2019

Question 4

 

Fig. 2 is the diagram of an alternator in the charging system of a motor vehicle.
question
     

  1. X is a major part of the alternator which comprises of an assembly of components.

    1.            
    2.           Identify the components in X.

    3.            
    4.          State the function of X in the operation of the alternator.

    5.            
    6.        State two symptoms of a faulty X in the operation of the alternator.

    7.           
    8.      Describebriefly how the components in X can be tested.

    9.  
      

        

  2.    In the operation of the alternator in the charging system, state:

    1.     
    2.     the function of the voltage regulator; 
    3.  
           
    4.      three symptoms of bad voltage regulator. 

    5.  

Observation

The expected answers were:


  1.      
        
    1. X – rectifier/diode assembly

    2.                                                                         

    3. Function of X in the operation of the alternator

    4. Rectification/conversion of a.c. to d.c.

       
    5. Symptoms of a faulty X in the operation of the alternator

      • Drop in charging output
      • Leakage of a.c. current into the electrical system

                                                                                                     

    6. How to test the components in X

    Alt.I

    • Set multimeter to a.c. or d.c. voltage

    • Turn the dial to diode-test/resistance mode

    • Connect the test leads to the diode

    • If a continuous sound is heard in only one direction, diode is in good condition

    Alt. II

    • Measure voltage drop across diode in forward bias mode

    • It permits current flow and measures 0.7/0.2 voltage value

    • It does not permit current flow in the reverse direction and does not measure voltage
    • The diode is in good condition
     
  2.   
       
    1. Function of voltage regulator in charging system
    2. To maintain constant output voltage even with varying load. 

    3.    
    4. Symptoms of bad voltage regulator
    • Dimming light in headlamps and dashboard elements

    • Pulsating light  in headlamps and dashboard elements

    • Dead battery

    • Unpredictable engine performance

    • Engine stalling

    • Engine sputtering

    • Intermittent acceleration

    • Over-charging

    • Under-charging

               
    It was reported that majority of the candidates that attempted question 4 responded well but for question (a)(iv) which required the candidates to describe how diode (X) can be tested.
    Majority of the candidates, including the high performing ones, did not describe the process of testing diodes appropriately.