Active Balancing for Efficient Management of a 4S1P LiFePO4 Battery Pack

This paper presents the implementation of an active balancing technique for the management of four Lithium Iron Phosphate (LiFePO4) cells of high capacity, connected in series (4S1P), which can replace the classical Lead-Acid battery of a vehicle or can be used in other 12 volts applications. The use of a Battery Management System (BMS) has major advantages, preventing overcharging and discharging of cells, reducing voltage imbalances between cells, and prolonging the service life of the pack. The developed active BMS is based on a transformer with the primary winding powered from the battery pack and the secondary winding switched to the lowest charged cell using relays. The measured parameters (voltages, current, and temperature) are displayed on a LCD and transmitted through an USB interface to a computer. The measurement results show that the proposed BMS can successfully balance the battery pack at 1.3 A, and up to a voltage imbalance of 2 mV.