To complete the battery charging to full capacity, the constant voltage charging mode is applied. In this mode a constant voltage ( max V ) is applied to the battery terminal and the battery determines the absorbed current. As the battery state of charge (SOC) increases, the battery current decreases under constant voltage charging mode.
Constant current charging is a method of continuously charging a rechargeable battery at a constant current to prevent overcurrent charge conditions. Constant voltage charging is a method of charging at a constant voltage to prevent overcharging. The charging current is initially high then gradually decreases.
In the constant current mode, a full charging current is applied to the battery and the battery voltage is observed. This mode of charging continuesuntil the battery voltage arrived to its full level ( max V ). In this case the battery is charged to about 70% of its full capacity.
The constant voltage method of charging batteries is one of the most common and simplest methods. It involves applying a constant voltage to the battery, typically around 14.4V for lead acid batteries, until the current flowing into the battery drops to a very low level. At this point, the battery is considered fully charged.
You can see this in the blue line in the graph. In this simulation the internal battery voltage (Vint) had only reached 4.0 V when the charger switched to constant voltage mode at 4.2 V. By the time charging current dropped to 10% it had risen to 4.18 V, and as charging continued it eventually reached 4.20 V.
The problem with this method is that the charging current flows in a large quantity at the final stage and causes over charge. Care should be taken to avoid charging for more than the specified charge period. (2) Constant current charging method This method consists of charging the battery with constant current.