I plan to use a relatively high-end microcontroller (Piccolo TMS320F28035, 12-bit resolution, +/- 4LSB offset, +/- 60 LSB gain) to measure voltage across stacked battery cells and control associated analog electronics to equalize their charge. The microcontroller will also store data in an eeprom memory (blackbox).
The current plan is to read up to 10 cell voltages. The problem is the large common mode voltage (each cell can go up to 3.5 V) - I cannot use isolated amplifiers such as INA124 or non-isolated high-precision INA117 due to high cost.
The current plan is to use voltage dividers (0.1%) at each tap and calculate cell voltages relatively to each other:
- V1 is measured directly
- V2 is calculated as measured V2 value less calculated V1
- and so forth
The problem with this setup is that the tenth measured voltage will suffer from high voltage-divider ratio and thus could be off by too much.
Another approach is to use a battery monitoring chip and use is as an analog front end (BQ77PL900) but the cost is quite high as well.
Are there better ways to precisely read battery cell voltages?