The BMS is aware of the nominal (normal) Internal Resistance of the battery pack based on the data entered into the Nominal Cell Resistance table as well as the Fault Cell Resistance table. These tables are used to determine the maximum allowable internal resistance for a cell before it is determined to be weak or faulty.
The BMS will also set a weak cell fault code if the difference between the open (sitting) cell voltage of any one cell and the average of the rest of the cells is too great. This typically indicates that the cell is either severely out of balance or has greatly diminished capacity.
The BMS is also able to determine if cells are simply out of balance (a correctable issue) or if they are low capacity (an uncorrectable issue). It does this by allowing the user to specify a maximum delta open cell voltage range for any cell both at the top (charged) end and the bottom (discharged) end. If the same cell is registering an abnormally high open cell voltage at the top end of charge AND an abnormally low open cell voltage at the bottom end of discharge then the BMS will flag this cell as low capacity. This can be extremely helpful for determining the overall health or state of a battery pack.
A weak pack fault indicates when the pack health drops below a programmed value.
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