Passive Balancer For Eight Cell Battery Lifepo4 Pack

Abstract

This Article deals with the passive balancer that is required in all multi-cell battery systems. The balancer is designed for eight LiFePo4 battery cells that are connected in series, to achieve the required voltage of about 28 V. Each cell has a capacity of about 9600 mAh, resulting in a 80 Ah battery back. The balance algorithm is performed by main STM32 microcontroller (MCU), which controls eight balancing transistors. For measuring battery cell voltages, there are two variants of cell measurement. The first alternative of cell measurement is a battery monitor IC, which is also capable of low side current measurement and as protection it also drives the low side current transistor switch, which protects powered device. Other options are measurement by 14-bit analog to digital converter (ADC) or with internal ADC of MCU. The balancer circuit also includes an RS485 interface for communication with other devices.