(ii) Watt-hour efficiency or (energy efficiency).
Now, we will study in detail both efficiencies:
Ampere hour efficiency or quantitative efficiency Is the ratio of quantity of electricity during discharge to the quantity of electricity during charging. But quantity of electricity is given as product of current in amperes and time in hours. Therefore, the quantitative efficiency is also known as ampere-hour efficiency.
Ampere hour efficiency = Ampere—hours on discharging/ampere—hours on charging
The ampere-hour efficiency of a lead acid cell is normally between 90 to 95% means about 100 Ah must be put back into the cell for energy 90 to 95 ampere-hour taken out of it. The reduction in ampere-hour efficiency is due to following factors:
(i) Due to self-discharge of the. plates caused due to local reaction,
(ii) Due to leakage of current because of faulty insulation between cells of the battery,
(iii) Gassing during charging. Energy Efficiency or Watt Hour Efficiency It is the ratio of energy, which a cell gives out during discharging and energy it requires regaining the original condition during charging.
= Energy during discharging/Energy during charging x 100
Watt—hours on discharging/Watt—hours on charging x 100
is also known as watt-hour efficiency. As the voltage on discharge is always less than voltage on charge, the watt-hour efficiency is always less than ampere-hour efficiency and varies 80 to 85%.
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