Q1: Does cell balancing move energy between cells?
A1: Cell balancing includes Active cell balancing and Passive cell balancing. The technology used in general electric vehicles, excluding buses and trucks, is Passive cell balancing, which aims to increase the charge in less charged cells by reducing the charge in relatively more charged cells through resistance.
Q2: After charging to 80%, the battery level increased to 82% after charging was complete. Is this due to cell balancing?
A2: Cell balancing operates during charging and does not function after charging is complete. The increase in battery level is due to the accuracy of the SOC (State of Charge) prediction algorithm. It is particularly problematic if the level increases beyond the charging limit. For example, if you charge to 100% but it actually reaches 102%, it can put stress on the cells. However, manufacturers do not show users a battery level above 100% even if it exceeds that.
Q3: How effective is passive cell balancing?
A3: Let's assume a Tesla Model Y with a 60 kWh pack. 60 kWh corresponds to 150 Ah based on 400 V. Passive cell balancing usually ranges from 100 mA to 300 mA. At 100 mA, if you charge for 1 hour, the balancing effect is only about 0.1 Ah. This translates to an improvement of only 0.07%, which means the effect is almost negligible. If you use slow charging for 10 hours, the improvement is still only about 0.7%, so there is some effect. Due to this issue, the larger the pack capacity, the smaller the cell balancing effect, making the manufacturing precision of the cell manufacturer more critical.
Q4: Does temperature have an effect?
A4: Yes, the lower the temperature, the higher the internal resistance of the cell increases exponentially, causing more deviation.
Q5: Does cell balancing occur while driving?
A5: This varies by manufacturer.
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