High Precision Cell-voltage Measurement by A Low Cost Micro-Controller for Li-ion Battery Packs Used in Electric Bikes

摘要

Voltage measurement on each cell of batteries is one of the most significant functions for battery management system (BMS) of lithium ion battery packs. To supply power for 24 V rating motor of electric bikes, we need at least seven cells connected in series. Voltage measurement on each connection node by an A/D converter built in a general purpose microcontroller is the most commonly used technique. It needs high resolution A/D converter to obtain satisfying resolution of cell voltage. The measurement resolution will be even worse for the case with more cells in series. In this paper, we present a front-end circuit to direct measure voltage of each individual cell to avoid the above issue. The measurement was accomplished by an 8×52 micro-controller and an 8-bit A/D conversion circuit. It has resolution as good as 7.8 mV, even better than that by an ordinary approach with a 12-bit A/D converter.