Page 73 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Positive Plate Pbo + H + H So = pbSo + 2H O
2
2
2
4
4
2
When the cell is discharged both plates are pbSo
4

Chemical action during charging
During discharging both plates are changed to lead sulphate. On the charging positive supply terminal is connected
to the anode of the cell. So that the current in the electrolyte is passing from cathode to anode in the electrolyte.
Sulphate ions moves to the anode and hydrogen ions react with the lead sulphate ions which enter into the
solution.

Positive Plate
PbSo + So + H So = pbo + 2H So 4
2
4
4
2
4
2
Negative Plate
PbSo + H = Pb + H So
4 2 2 4
During charging
1 Both anode and cathode become lead sulphate it is whitish in color
2 Due to formation of water specific gravity of acid decreases
3 Voltage of the cell decreases.
4 The cell gives out energy
During discharging

1 The anode become dark chocolate brown and cathode becomes gray metallic color
2 Due to consumption of water, specific gravity of sulphuric acid is increased
3 Voltage of the accumulator rises
4 Energy is absorbed in the cell

Indications of fully charged cell
1 The visible indications of fully charged cell
2 The color of the electrodes positive plate chocolate brown and negative plate slate gray color
3 The gassing at the electrodes. A fully charged accumulator gives of oxygen and hydrogen freely as gas
bubbles
Preventive maintanance of lead acid cell
The following steps should be adopted for Preventive maintenance of lead acid battery.
• Level of the electrolyte: - Before putting a battery on charge, always maintain the level of the electrolyte 15
mm above the plates. For this distilled water should be added.

60

CITS : Power - Electrician & Wireman - Lesson 13-19