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Thanks for the clarification. I guess I should read *ALL* of the spec sheet before commenting.
To get a decent range on discharging your pack, I would have expected you to have to adjust the output on both power supplies. See my notes further below.
Regarding using an Op-amp to amplify millivolt signals, I have had noise problems doing that sort of thing (in the distant past). The commercial applications that I have seen (maybe 10 years ago) appear to use a variant of a wheatstone bridge to do that job. I expect that the instrumentation amplifiers are much better now. Let us know how it works out for you.
My notes - to see if I understand what you are doing now and trying to do
Do I understand?
- you are using a potentiometer in your present charging setup
- you plan to use a pwm signal (DAC) to the calibration input on the power supply to vary the output voltage +/- 5%
- you will stop using the I2C to get information from the power supply and use a differential input on the millivolt shunt for each power supply to determine output current, load sharing, etc
If that is the case, since you are making it work right now,
- you are charging your cells to 102.2V (3.65V each) plus your diode drop
- you've added several diodes so that your power supplies output maximum (108V) and your batteries receive 102.2V
- your charger can drop 10.3V to minimum voltage, making 91.9V at the pack terminals
- DIYelectriccar has a couple of postings listing Sinopoly charge and discharge curves. I don't know if they match your batteries, but using them you can discharge your pack down to about 20% - 3.28V. Sounds about right to me.
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