Auto Electrical Works Paper 2, WASSCE (SC), 2018

Question 4

 

Fig. 3 is a diagram of an alternator circuit.


(a) Identify the parts labelled P, Q and R.  
(b) State one function each of the:
(i)         rotor;
(ii)        diodes;
(iii)       voltage regulator.
(c) State the steps involved in testing a faulty diode.

Observation

      The expected answers were:

         

(a)

P – stator                                            
Q – rectifier/diode assembly                          
R – slip rings  

(b)

(i)        Rotor – rotates to produce/generate electric current in the windings.           
(ii)       Diodes – convert alternating current to direct current.                      

(iii)      Voltage regulator – maintain constant voltage supply/stabilizes voltage supplied.        

(c)        Steps involved in testing a faulty diode

  • Turn off power to the circuit
  • Discharge the capacitors
  • Set the multitmeter to diode test mode
  • Connect the leads to the diode/insert the diode leads into its provision in the meter, read and record the displayed measurement
  • Reverse the test leads, read and record the displayed measurement
  • If the diode is a good one, the silicon type will display 0.6-0.7V and while germanium will display 0.2-0.3V in forward bias. (Analysis of the steps)

Majority of the candidates that attempted Question 4 responded fairly well.