ZIMSEC O Level Combined Science Notes:  Lead acid accumulators

  • These act as a storage cell
  • Electrical energy is passed into the cells during the charging cycle
  • It is stored in the form of chemical energy
  • \text{Chemical Energy}\xrightleftharpoons[charging]{discharging} \text{Electrical Energy}
  • Lead acid accumulators are known as secondary cells
  • Secondary cells-can be recharged once the voltage drops
  • Charging is done by passing a current through the cell in the opposite direction
  • This supplies the current
  • Inside the lead acid accumulator
  • The positive electrode is made up of lead (IV) oxide and
  • The negative terminal is made up of lead
  • The electrodes which are in the form of plates are made in grid form
  • Sulphuric acid is used as the electrolyte
  • When discharging (supplying current)
  • Both plates turn to lead and the density of the acid falls
  • The voltage of each cell remains constant at 2 V
  • Until the battery is nearly drained/completely discharged
  • It then drops to 1.8 V
  • The state of discharge can be checked using a hydrometer
  • The density of a fully charged cell is 1.25 and
  • In a flat cell is falls to 1.1
  • During the recharging cycle the positive terminal turns back into lead (IV) oxide and
  • the density of the acid increases
  • Care should be taken during recharging  not to overcharge the cells
  • An explosive mixture of hydrogen and oxygen is formed if this occurs
  • Distilled water should be added to cover the cells with electrolyte
  • The level of the electrolyte should be checked before recharging
  • Lead acid accumulators/batteries are often used in cars and
  • solar systems

To access more topics go to the Combined Science Notes page.

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