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

Question 1

 

  1. (a)        Two 12 V, 45 AH lead-acid batteries were connected in series for a practical session in an Auto Electrical Works (AEW) workshop.

    1. State the meaning of 45 AH in relation to battery capacity.
    2. Draw a circuit diagram for the connection.
    3. Calculate the total:

    (I)  voltage;
    (II) capacity.


    (b)        Table 1 contains some common faults in a lead-acid battery.
    Table 1


    S/N

    Fault

    Symptom of fault

    Remedy

    I

    Lagging cells

     

     

    II

    Corrosion of terminals

     

     

    III

    Short circuit

     

     

    IV

    Sulphation of plate

     

     

                            Complete Table 1 by stating one symptom of fault and one remedy for each fault listed.

Observation

          The expected responses were:

  • (i)   The battery delivers a current of 1 A steadily for 45 hours.                          

(ii)  Diagram of two batteries connected in series
                                  

                  

(II)       Total capacity remains same for batteries connected in series.
Hence, total capacity = 45 AH                                                           

  •                                                                   Table 1

 

S/N

 

Fault

 

Symptom of fault

 

Remedy

I

 

Lagging cells

  • No crank after a long rest
  • Sudden voltage drop
  • Replace battery

II

 

Corrosion of terminals

  • Low voltage supply by cell/battery
  • Wash terminals and apply petroleum jelly/grease

III

 

Short circuit

  • No voltage supply
  • No engine cranking
  • Replace battery

IV

 

Sulphation of plate

  • Low voltage supply
  • Fast discharge
  • Low cell capacity
  • Low electrolyte density
  • Premature gassing
  • White deposit of negative plate
  • Top up electrolyte and recharge
  • Replace battery

                                                                                                                                               

Question 1 required candidates to show understanding of basic terminology and total output of a combination of batteries. More so, other part of the question required candidates to show familiarity with some common faults in a lead acid battery. The Chief Examiner reported that majority of the candidates that attempted question 1 could neither show understanding of the effect of combination batteries nor state the symptoms and expected remedies to common battery faults given.