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I tried to use this module for a 4S 18650 battery pack: enter image description here Beside charge controlling it is supposed to balance cells and this is where my issue emerges. If I put some unevenly charged cells in the pack, lets say 3 cells at 3 V and one at 4 V, and connect it to a 16.8 V power supply with current limited to max 500 mA. Cells will charge till the cell that initially was at 4 V reaches 4.2 V (HY2213-BB3A overcharge detection voltage). In this point the balancer activates and discharges this cell at 60 mA. But since charging current is way more than that, charging continues till this particular cell reaches 4.25 V (the DW01 Ics overcharge protection voltage). At this moment, the DW01 IC stops the charging current and the balancer drains this cell till it drops back to 4.19 V (HY2213-BB3A overcharge release voltage). But this voltage is not yet low enough for the DW01 IC to release and let the charging process continue (DW01's overcharge release is at 4.05 V).

So now we have 3 cells at slightly above 3 V and one at 4.19 V and the charger is disconnected by DW01's command.

How is this module supposed to balance these cells?

AKTanara
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    maybe the device is not designed to do that ... refer to the user manual – jsotola Jun 08 '23 at 22:52
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    Maybe it is supposed to balance the batteries, but can't work with that much imbalance. Or maybe it is just not very good module. Let me guess, it was cheap, bought from chinese online store and there is no manual for it? – Justme Jun 08 '23 at 22:58
  • @Justme Thanks for the comment. I have asked and got a comprehensive answer about balancing capacity here: https://electronics.stackexchange.com/questions/669107 so I do not think that it is the matter of amount of unbalance or charging current. Apparently it is a faulty design. Yest it is a cheap 2.5$ module without a manual. – AKTanara Jun 09 '23 at 05:19

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You are correct.

It's a faulty design, for the exact reasons you explained so well.

Any BMS for more than one cell in series that uses the DW01 IC (designed for a single cell) is a troubling one.

Return that BMS to the vendor and explain why.

Davide Andrea
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  • Thanks. I have an alternative simple and cheap design in my mind that probably will ask today and I hope you do not mind taking a look at it and give your precious opinion about it. Also, thank you for editing the text of my question. – AKTanara Jun 09 '23 at 05:56