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

Question 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.

State the meaning of 45 AH in relation to battery capacity.
Draw a circuit diagram for the connection.
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.