The individual cells in a battery pack naturally have somewhat different capacities, and so, over the course of charge and discharge cycles, may be at a different (SOC). Variations in capacity are due to manufacturing variances, assembly variances (e.g., cells from one production run mixed with others), cell aging, impurities, or environmental exposure (e.g., some cells may be subject to additional heat from nearby sources like motors, electronics, etc.), and c.
How to balance a battery pack correctly?
needs two key things to balance a battery pack correctly: balancing circuitry and balancing algorithms. While a few methods exist to implement balancing circuitry, they all rely on balancing algorithms to know which cells to balance and when. So far, we have been assuming that the BMS knows the SoC and the amount of energy in each series cell.
Battery balancing equalizes the state of charge (SOC) across all cells in a multi-cell battery pack. This technique maximizes the battery pack's overall capacity and lifespan while ensuring safe operation.
So, balancing is done during the charging phase rather than the discharging phase. Remember balancing wastes a small amount of energy in order to equalize the cell groups in the battery. Balancing also in most cases starts when cell groups begin to be 4.0v or above.
Battery balancing can be performed by DC-DC converters, in one of three topologies: Typically, the power handled by each DC-DC converter is a few orders of magnitude lower than the power handled by the battery pack as a whole. In passive balancing, energy is drawn from the most charged cell and dissipated as heat, usually through resistors.
Selecting the appropriate battery balancer depends on several factors: Battery chemistry: Ensure compatibility with the specific battery type (e.g., lithium-ion, LiFePO4, lead-acid). Number of cells: Choose a balancer that supports the required number of cells in series. Balancing current: Consider the required balancing speed and efficiency.
What are the different types of battery balancing?
In general, battery balancing methods can be categorized into the following types: Passive balancing dissipates excess energy from higher-charged cells as heat, while active balancing employs a switch matrix and transformer to transfer energy between individual cells.