My company is designing a 4 cell BMS. We recently did a redesign of our cell voltage measurement circuits and are having major issues.
The first stage of each amplifier is a differential opamp with unity gain. For cell 1 we take the difference between gnd and CV1, for cell 2 we take the difference between CV1 and CV2, so on and so forth.
For cells one and two the differential amplifiers are working perfectly. However, for cells 3 and 4 the amplifiers are outputting voltages much high than the actual cell voltage. The output from the cell 3 differential op-amp is around 7 volts and for cell 4 around 11 volts.
The second stage of the amplifiers is meant to lower the voltage to an acceptable range for the ADC. Unfortunately, we used a non-inverting op-amp and have a gain greater than one. A gain of around 0.7 is desirable.
Thanks in advance for any help!