Corolla eFX circuit diagram

During the last weeks I have spent hours and hours in studying different batteries, chargers, LiFePO4 protection modules, cell balancing modules and battery management systems. I'm pleased to finally have made up my mind about the solutions that will be used in this electric Corolla. I'm even more pleased about the circuit diagram that turned out to be quite simple and low cost yet providing all the features I wanted.

LiFePO4 Protection Circuit Modules (PCM) will be used in both 12,8V and 76,8V battery packs to monitor that each cell's voltage is kept between 2,0V and 3,9V. If the voltage of any cell goes outside of this range the PCM disconnects the P- terminal from the battery packs negative terminal. If that happens in either of the battery packs, the Corolla will stop immediately. This feature is only the last resort to protect the LiFePO4 cells from severe over- or undervoltage. In normal conditions the driver is responsible to maintain acceptable charge level by charging the batteries often enough and not trying to drive too far.

The PCM's that will be used have integrated balancing circuits but the balancing current is typically only less than 100mA. I think it is quite low for 60Ah batteries and a 10A charger so I decided that 1,7A Cell Balancing Modules (CBM) will be installed parallel with each cell to help the situation.

Now that the plan is done it's time to purchase the rest of the components and complete the project. Let's see how many changes will be needed along the way!