I am using 4 Stacked BQ76PL536 in combination with a TM4C123G controller on a 14s battery system in a 4,4,3,3 configuration. The system is online since late 2015, with some longer offtimes during winter.
As i tested one battery, in total with 140 cells in series so 10 BMS boards, i recognised that the system is tripping overvoltage with the secondary protection but the cell voltages a actually lower.
The AFE is set 4.2V and 1000ms delay. This was verified in multiple tests and worked for 3 years. Just now the OV bits and the secondary protection are tripped before the voltage of 4.2V is reached.
We are talking about voltages between 4.12V to 4.18V depending on the boards, most of the time if i am rebooting (reinitialize and readdressing the AFEs) the cells which are indicating a OV are changing. They are not even the highest cells. CellVoltages are acccurate as always within +-2mV. For now i have lifted the OV Limit to 4.4V, but this is not acceptable since all the hardware safety circuits are now inactive and the safety relies on the software.
So what is happening here? I have no idea what to do! Let me know what data you need to know so we can figure this out.