Question: 4 packs in a parallel system, battery SOC dropped from 24% to ZERO suddenly. 10 days later, the master battery was found seriously over-discharged and the voltage was only 6.14V, while the rest 3 packs’ voltages were about 44V. Why?
Firstly, the loss of communication between the battery and the inverter is the main reason. If the communication cable is freely plugged into the inverter, the connection is easy to be loose. Thus the communication is lost, and it is recommended to fix the inverter side of the communication cable in case of freely plugged.
Secondly, the discharge mos keeps closd in sleep mode is the reason why the master suffered seriously under voltage after the communication between the battery and the inverter is lost. As we know, when pack voltage is under 48V or cell voltage is under 2.8V, meanwhile, no current, then the battery will enter sleep mode. So, in this case, the master entered sleep mode before it discharged to under-voltage-protect. Then the communication between batteries lost and the rest pack stopped discharging and charging. As the discharge mos was still on and the discharge current was less than 1A which could not be measured effectively by BMS, the master battery could not be waken up and disconnect discharge mos when under-voltage-protect, it just kept discharging and suffered seriously under-voltage. To solve this problem, the discharge mos open in sleep mode will be activated in the upgraded BMS.
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