The traction battery in an electric vehicle is actually made up of thousands of individual cells, over 7,000 in the case of the Tesla Model S 85kWh.
Battery management systems [BMS] are just as critical to electric vehicle performance and range as is battery technology. After all, a battery is only as strong as its weakest cell, so a good BMS will keep all the cells more or less equalized and allow for even cycling. Fraunhofer Institute for Integrated Circuits IIS researchers are testing their new BMS in a small F1-style e-racer called EVE.
The BMS in this e-racer is unique in that it uses no direct-contact measurements of battery capacity, charge or discharge. Using a 3D hall-effect sensor, which is sensitive to magnetic fields, Fraunhofer’s BMS can accurately measure how much energy is transferring to and from the cells in the traction battery. Other sensors detect temperature and voltage, and the BMS uses all these measurements to manage the electric vehicle battery precisely.
Dr. Peter Spies explains, “Until now, a battery system was able to provide only as much energy as was available in its weakest cell. The energy stored in other cells remained unused. Our BMS has an active cell balancing system that moves energy between stronger and weaker cells. This means that all cells share the load equally, allowing the maximum capacity of the battery as a whole to be utilized.”