Yes, I know that there are dedicated battery stack monitors available, but in this case is the stack small and voltages reasonable. Four 3.2V cells give 12.8V. What I would like to do is to monitor each cell and disconnect the pack in case the voltage of one individual cell is outside the allowable range, being 2.5 ..4V.
The cells will be sitting in a boat. Used over summer and removed and top-balanced every winter. They will be charged from a solar cell, using a MPPT charger.
I did a quick simulation in LTSpice and also read the LT6015 datasheer. I have attached that file and I apologise for the messy schematic showing the opamps for two cells. LTSPice absolutely refused to play ball when I turned the opamp around
I realise that the resistors need to be matched for the circuit to work properly. The idea is to have the measued voltages VC1, VC2 etc readable from a MCU as well as fed into comparators for the disconnect logic.
Comments? Would this be a workable solution, given the design criteria outlined?
The LTSpice file
Did you attached the LTspice file? Could not see it. You can zip it before attaching.
Here it is. The webinterface did appartently not like the plain asc file
It seems to be workable. If you need well matched resistors, you may use LT5400-2 which can give you up to 0.01% matching. You could also add some capacitors for filtering in parallel with the feedback resistors R2 and R6 and R4 and R8 to ground. This could give more protection against stability issues, ringing, noise and oscillations.
Another possibility is to use LT1991, which already have integrated resistors well matched. Also, this part already have feedback capacitance integrated as well.
Thanks! Yes, I left out the caps in the simulation for clarity. I will look into your other suggestions and collect parts for a prototype!