The battery management system (BMS) developed by Fraunhofer IIS measures the current, voltages and temperatures of the battery cells. Based on the measured values the state-of-charge of the cells is calculated. So far the capacity of a serial multi-cell system is limited to the capacity of its weakest cell in the chain. Discharge has to be interrupted when the low-voltage limit is reached. Valuable cell energy of the other cells is lost and cannot be used.

This is where the battery management systems of Fraunhofer IIS come into play. In order to fully discharge all cells, the energy of the stronger cells has to be transferred to the weaker cells. When the BMS detects differences in state-of-charge, energy transfer from one cell to another is initiated with the help of a newly developed active balancing. This way the system efficiency is maximized and the power of every battery cell can be used. Fraunhofer scientists were the first to implement this innovative battery management technology. What is more, active balancing of energy reduces reduces the waste heat in the accumulator, which is generated i. e. by passive balancing.

Powerful battery systems are used in i. e. electric and hybrid vehicles and in small, light-weight electric vehicles, like wheelchairs or electric bicycles. With the help of the Fraunhofer battery management system it is possible to significantly increase the range of electric vehicles.

Fraunhofer showcases its latest battery management systems and efficiency maximizing technology at the Munich fair Electronica from November 9 to 12, 2010.