Charger Device for Lithium Polymer (LiPo) Battery

Figure 1 

The project is a single PCB where 3 LiPo battery chargers are combined with an output voltage of 4.2V for each charger.

The chargers are cascaded in order to become applicable for LiPo battery pack with 2 or 3 cells. A 3X8 VAC transformer is also used in this circuit. LiPo battery chargers could become widespread in the future for several applications and this can provide a big help.

Using the device, any 2-cells Li-Ion battery pack can be charged with a maximum current of around 650mA since the design of the circuit is for batteries with 900mAh or higher rating but the circuit should not be used for Li-Metal batteries. The device can be powered by a source from a car’s cigarette lighter or from a 12V Gel cell with power panel. Likewise, an old wall transformer with 12V DC and 800mA can be used.

For Panasonic, the recommended charging should be at a constant current of 0.7C until reaching 4.2V/cell. Until the current drops to 0.1C, the constant voltage is to be used where the charging should stop. Due to the voltage charge limitation to 8.4V, the circuit operation is simplified.

Click here to see the rest of the project.