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Trying to figure out how to use the BMS 4S 40A Li-Ion protecting balancer board that I got off Ebay. Revision 2.3, photo and schematic is attached. I am building a power bank. Got some new NCR18650b's. The voltage of all cells is the same: 3.7-3.71 V. I soldered the cells in correct order, 0, 4.2, 8.4, 12.6, 16.8 V. The board outputs 14.8 V and responds to load normally.

Now, I'm trying to charge the batteries using a CC-CV step-down set to 16.8 V / 1.5 A. However, whenever I connect charger, voltage at the BMS output immediately rises to charger's voltage, i.e. 16.8 V. The charging current at the batteries, naturally, is zero. Battery's voltage remains at 14.8 V. MOSFET switches at the board (the ones at the right) turn off when charger is connected, and 0 appears at their gates (probably because the MMBT5551 turns on). When load is connected, they are on, as they should be. The other 5 MOSFETs (left side) are always on.

What am I doing wrong, please? I have no experience with these boards. Could the board be faulty?

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  • \$\begingroup\$ Try charging it with a real lithium battery charger instead of a CV-CC power supply that is not a real lithium battery charger. \$\endgroup\$
    – Justme
    Commented Oct 15, 2021 at 9:34

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Turns out one of DW01A chips was soldered in the wrong orientation. After resoldering, the BMS is working as intended.

enter image description here

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