What is the Keheng BMS parallel module?
The main function of the Keheng BMS parallel module is to manage the current between multiple battery packs connected in parallel. When two or more battery packs are connected in parallel, the state of charge (SOC) of these battery packs will converge. This means that the current will flow from the battery pack with the highest charge to the one with the lowest charge until it reaches the same SOC and, thus, the same voltage.
For Li-FePO4 batteries, this energy transfer can be very significant, resulting in high currents that may exceed the capacity of the battery management system, thus causing damage to the Li-FePO4 battery. The charging curve of the Li-FePO4 battery is relatively flat, and even if the voltages are very close, there may be significant differences in SOC between different batteries. For example, the voltage between two batteries may only be 0.1V difference, but their SOC is very different.
When two or more battery packs are connected in parallel, the module will limit the amount of current transfer between the battery packs through the KAHN Parallel Module. This protection protects the battery management system and the batteries from possible damage.
One might argue that if two or more battery packs are always connected in parallel, they will naturally equalize. While this is theoretically true, in practice, the balancing process may result in high current transfers. Example:
- Before connecting battery packs in parallel, it is important to make sure that all cells are balanced to ensure that they have the same SOC. Otherwise, they will be balanced when they are connected.
- Suppose two battery packs are connected in parallel, and one of the packs is disconnected by the BMS due to a triggered protection parameter (e.g., a change in battery voltage). In that case, the remaining pack will continue to exchange current, thereby increasing the difference in SOC. When attempting to reconnect the battery packs to the parallel circuit, the battery packs will attempt to rebalance, resulting in unrestricted current transfer.
The use of a BMS-equipped ACE paralleling module for each battery pack regulates the current between the cells, preventing any potential damage to the BMS and the cells.