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What is cell balancing // Why does a battery pack need it? How does it work?

What is cell balancing // Why does a battery pack need it? How does it work?

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  A battery back for micro-mobility vehicles on average consists of 40 cells.  Every single cell differs from one another. This is caused by minimal variances in the manufacturing and assembly process. Those differences manifest in the rated capacity, internal resistance, self-discharge rate, and the charge & discharge efficiency.

  The lowest capacity cell dictates the end of the charging and discharging process. The remaining capacity in better performing cells is not released or they are not completely charged. This means that an unbalanced cell pack is not used to its full capacity, over time the range of the used capacity gets lower and lower. Virtually the number of cycles of the battery pack increases, the battery ages faster.

  The variances of the cell's capacities cannot be avoided and equalized but by balancing the cells with the help of the battery management system (#BMS) the condition (State of health – #SoH) of the battery pack is improved.

  There are two methods: Active and passive cell balancing.

  Passive balancing uses resistors to transform the energy from the most charged cells and transform it into heat. The capacities of the individual cells are leveled. The limitation is given by the system’s ability to absorb heat, else there is danger, the cell chemistry, and BMS are damaged.

  Active balancing uses the excess energy from the most charged cells and transfers it to the least charged cells. It requires a complex circuit and battery pack design: The costs and size of the device increases.

  So, the consideration of what method to apply depends on the actual application and price target of the vehicle. The Greenway team always discusses and evaluates with their clients the available options to suggest the best solution for the customized battery pack