The basis of the charger design is 90 quarter brick DC/DC converters, so I got 100 just incase. I may use the same converters to charge/balance the 12v system battery as well. Each DC/DC converter will accept 36-75v input range and by default puts out 3.3v, however this output will be adjusted up 10% to put out 3.65v which is the perfect CV charge voltage for many LiFePO4 cells.
The 630 cell battery pack will be broken down into 6 individual battery boxes each containing 105 cells and one charger board which will contain 15 dc/dc converters. I’m still deciding if I should use connectors, or wires soldered directly to the board to connect from the board to the cells. The inital board design is shown below, which will be a 4 layer PCB roughly 6″ x 12″ which will be mounted above the headway cells, with very short connecting wires from the PCB to each buss bar. There is no longer the need for a BMS because each cell is effectively charged individually to the preset 3.65v.
Each battery box will be roughly 6″ x 12″ x 24″ which will make it fairly easy to mount and integrate into the car. The DB25 connector will connect each battery pack to the Arduino which will monitor each cells voltage. There are fuses onboard that will protect the pack and wiring from shorts or other problems.
The power supplies can accept between 85-264v AC so I simply need a 3 prong grounded plug for the charge port, the standard connection for this voltage and current range is the NEMA L6-20, so behind the fuel filler door will be something like this:
This will allow me to plug into any available 110/220v outlet to recharge, it would also be technically possible to plug directly into a 48v DC power supply or battery (36-75v actually due to the wide input range of the dc/dc converters). This would bypass the AC power supplies and require a high current 48v DC connection.