Batteries Interview Question Answer - 3

Which are the active materials used in the lead acid cell?

Active material in the lead – acid cell
  • Positive plate – PbO2
  • Negative plate – Pb
  • Electrolyte – Dilute Sulphuric acid ( H2SO4)

How the positive and negative plates are arranged in the cell?


What percentage of water does the electrolyte consists of?

Water : Sulphuric acid = 3: 1

Describe the chemical changes in the positive plate, negative plate and electrolyte in the lead – acid cell.

Chemical changes during charging
  • The cell voltage increases.
  • The specific gravity of the electrolyte increases.
  • The positive plate becomes dark chocolate and negative plate becomes grey in colour.

Chemical changes during Discharging
  • Cell voltage decreases.
  • The specific gravity of electrolyte decreases.
  • The anode and cathode plate became PbSO4 and whitish in colour.

Why the specific gravity of electrolyte decreases during discharging of cell?

Due to formation of water

Why the specific gravity of electrolyte increases during charging of cell?

Due to consumption of water

Which technique is used to reduce internal resistance of a cell?

  • When all the positives and negative plates are connected in parallel, the internal resistance is reduced.
  • As the length of electrolyte between two plates decreases, internal resistance also decreases.

Give reason : The number of negative plate is one more than the positive plate in the cell.

There is a negative plates used at both ends of cell in order to increase mechanical strength.

Which material is used for separator in the cell?

Glass wood mate, cedar wood, micro porous rubber, micro porous plastic etc...

Give reason : The Watt hour efficiency of the cell is always less than the ampere here efficiency.

Watt hour efficiency
  • The watt hour efficiency takes into account varying the charging and discharging voltage of the cell whereas it is not consider for the ampere hour efficiency therefore the ampere hour efficiency is less than the watt hour efficiency.

Describe the effect of high charging and discharging rate of cell.

Watt hour efficiency decreases

Why the efficiency of the cell is not 100%?

Efficiency of cell
  • The efficiency of the cell isn’t 100% due ( a ) Gassing takes place during charging ( b ) Self inductance of the plates ( c ) Leakage current.

Which are the factors depends upon open circuit voltage of the cell?

Factors depend upon open circuit voltage
  • Charging time
  • Specific gravity of electrolyte
  • Temperature

At which condition the cell voltage does not appear?

When the specific gravity of electrolyte is equal to density of water.

Give reason : The discharge voltage of the lead acid cell should not drop below 1.8 V.

Discharge voltage
  • If the discharge voltage of the lead acid cell drops below 1.8 V, insoluble lead sulphate is formed on the plate which increases the internal resistance.

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