3 Stage Battery Charger

3 stage battery charger is the best way to charge batteries efficiently and fast rather than using  a constant voltage or constant current charger.In constant voltage charger for a 12 V battery a constant voltage of around 13.8V or higher according to the battery specifications is applied which takes long duration for charging the battery and may over voltage and damage the battery if not cut off after fully charged.Similarly in constant current charger a current source is used to provide constant current to charge it is not good because we need to provide some time for battery to recover while giving charge which is not provided in constant current method.

The three stages of 3 stage battery charger are

1)Constant Current (Bulk Charge)
2)Constant Voltage(Absorption Charge)
3)Constant Voltage(Float charge)


In the stage of bulk charge a current source is used to apply  constant current to the battery of 20% (the value depends on he manufacturer specifications)of battery capacity specified at 20 hours i.e C@20.
            Then a constant voltage is applied across battery of 14.4 V(2.4 to 2.45 V per cell) till the stage the amount of current battery takes come to a point of 0.1 C.Then a constant voltage of 13.8 volt is applied to compensate self discharge of the battery .

in the above circuit the switching is done by reading the current using ACS712 and voltage by using voltage divider circuit and the data is given to micro controller like Arduino for switching purpose