Daniel
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- 2021 Taycan 4 CT
Audi Etron GT ( brother of the Taycan) balancing processThe BMS takes some juice from the single cell group with the highest voltage and shunts it to the single cell group with the lowest voltage. Then it waits a bit and repeats the cycle. Eventually all groups are brought to within the tolerance set in the BMS - anything from one to a few millivolts.
Imagine this as a separate little module with separate wires to each cell - and that is in fact how it is often implemented, separate from the charger, which stuffs electricity into the battery pack as a whole.
From a technical perspective, there are several different ways to shuffle electrons from one cell to another (https://en.wikipedia.org/wiki/Battery_balancing) but basically it's all about taking from the highest voltage and sending to the lowest voltage.
Importantly, the maximum balance current is very low, which is why fast charging doesn't leave enough time for much balancing.
Source: @rs38 https://static.nhtsa.gov/odi/tsbs/2021/MC-10190946-0001.pdf
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