All of GeePower battery cells in a pack are with very high consistency. In a pack, each cell has its own sole electronic code (ID number) for quality control after-sale. Assume one cell in a pack is damaged in any reason after several years later, we could provide a exactly same cell to the client to replace this damaged one (same voltage, capacity, impedance,etc.) , in order to make sure all of the cells in this pack with very high consistency. GeePower has a strong system working for this.
GeePower Li-ion battery pack can be assembled in series and parallel with a battery management system (BMS). A BMS that is able to measure each cell’s resistance and compensate its cutoff voltages accordingly can make better use of a battery’s capacity. Recoverable cell capacity, effective cell capacity, and cell resistance versus cycles.
Why need a BMS?
In a high-voltage battery with many cell in series, though, there is a much greater chance that the overall pack voltage is not evenly divided among its cells. (This is true for any chemistry.)
Consider a four-cell LiPo battery, charged up to 16.8V. If the cells are perfectly balanced, the total voltage will be equally divided into 4.2V per cell(Figure1 a). In practice, the cells will be unbalanced, and one will be the first to be fully charged and then be overcharged. Li-Ion cells do not deal well with overcharging.
Once charged, they cannot take more current ad the other cells in series get their needed charge. Instead, their voltage rises rapidly, possibly to dangerous levels. In this example(Figure1 b),the second cell is overcharged to 6.3V, while the other ones are around 3.5V. Despite the fact that the total voltage is 16.8V, three of the cells in this battery are not fully charged, and one of its cell is in danger of thermal runaway. Therefore, a system that relies on the total battery voltage to determine when to stop charging the battery (such as a CCCV charger) gives the user a false sense of security; that system will overcharge some cells, and will create a safety issue as some cells with be overcharge to dangerous levels. It is therefore essential that a BMS monitor such a battery, first and foremost to prevent any cell from being overcharged, and optionally to balance the battery to maximize its performance.
Now consider the same battery, after it has been discharged down to 12.0V. If the cells are perfectly balanced, the total voltage will be equally divided into 3.0V per cell (Figure2 a). In practice, the cells will be unbalanced, and one will be the first to be fully discharged, and then be overdischarged. To varying degree,Li-Ion cells do not deal well with overdischarging. If their voltage is allowed to drop below a certain threshold, irreversible damage may occur. In this example (Figur2 b), one cell is overdischarged down to 1.5V, while the other ones are around 3.5V. Despite the fact that the total voltage is 12V, three of the cells in this battery are not fully discharged, and one of its cells is being damaged. Therefore, a system that relies on the total battery voltage to determine when to stop discharging the battery (such as a motor controller with a low voltage cutoff) gives the user a false sense of security; that system will overdischarge some cells, damaging them. It is therefore essential that a BMS monitor such a battery to prvent any cell from being overdischarged and damaged.
(Figure1 a & b ) Four-cell battery, discharged: (a) balanced and (b) unbalanced. One cell is in danger of thermal runaway.
(Figure 2 a & b) Four-cell battery, discharged:(a) balanced and (b) unbalanced.
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