Trickle charging:
1.When a battery is kept as an emergency reserve, it is necessary to ensure that it is fully charged all the time and ready for service at any time.
2. The charged battery always loses some of its charges due to internal leakage and other open-circuit losses.
3. In order to compensate for such a loss of charge the battery is kept on trickle charging.
4. Trickle charging takes place at a very small charging rate I.e.charging current is very small.
5. Typically the trickle charging current is less than 1% of the normal charging current of the battery.
6. Note that the discharged batteries are first charged are their normal charging rate and once fully charged, are switched over to continuous trickle charging.
7. The trickle charging is necessary to keep the battery fully charged always. It is used for compensating for the charge lost due to the internal discharge of the battery. The trickle charging current is very low.
Boost charging (Importance of Initial charging):
1. If a lead-acid cell is not charged completely or not fully charged periodically then the lead sulphate formed during discharge is not converted back into pbO2 or Pb.
2. This is unreduced pbso4 gets deposited on the plates. This process is called sulphation of the plates.
3. Pbso4 is in the form of tiny crystals which gradually increase in size if not reduced by charging a cell thoroughly.
4. The effects of sulphation are: 1. Increase in the internal resistance. 2. Reduction in capacity and efficiency.
5. Sulphation can also take place if the battery is overcharged or left uncharged for a long time.
6. The sulphated cells can be cured by giving them a successive overcharge called Boost charging.
7. Boost Charging: When the battery is being charged for the first time, or when it is being used after a long time, the boost charging mode is used, where the cell voltage is raised above 2.4 v up to 2.6 v.
8. The boost Charging is used for breaking down the crystalline pbso4 which is formed when the battery is not in use for a long time.