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How to DIY Charge-Balance 4 Li-ion 2000mAH

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Psi:  You got that right.  I found a mention of this technique while googling that attempts to use a 4066 analog gate for this task, but IMNHO this idea is not to be tried without adequate ventilation and a fire extinguisher close by.

BIAC, its not efficient and ends up robbing Peter to pay Paul.

This idea shows some merit in preventing some cells in a pack from being reversed-charged and damaged (and gain extend the use of  nearly over-discharged cells to achieve some more time of the use of a battery pack.) This might be important where even a short time of extended operation of a battery in a device would could be well-appreciated, worthwhile or mission critical.

David Hess:

--- Quote from: SuzyC on October 21, 2021, 01:51:59 pm ---Balancing a pack during charging does nothing to prevent some battery cells in a pack from becoming out of balance in use, especially when the battery pack is being used near the discharge cutoff voltage. This is because the cell/cells that were fixed-up by charge balancing would likely reach their fully discharged voltage faster than cells in a pack that were functioning better and didn't need balancing in charging.
--- End quote ---

That is always going to be the case if different cells have a different capacity.  Either charging will be terminated early to prevent overcharging some cells, or discharge will be terminated early to prevent over-discharging some cells.  Charge balancing is about maintaining the maximum available capacity of a battery pack by preventing cells from becoming further out of balance.

It should be better to redistribute charge between cells during discharge, and this is feasible, however it comes at a high cost for only a minor improvement in capacity.

In the case of the Milwaukee M12 battery system where the cells are only monitored, charge balancing can be accomplished through controlled overcharging because LiFePO4 cells are used.  Lead-acid and NiCd batteries can also be balanced through controlled overcharging.


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