Dear battery people,
I am planning to make a platform in which you can use second life 18650 cells. I have read and learned a lot there is to learn about safety, balancing, BMS, etc…
But specifically to second life cells, I am looking for a way to detect when a specific cell in the whole system is really EOL. My take on it (and correct me if I am wrong) is that as long as there is any usable capacity in a cell, it can stay in the system. Only when it’s really dead and just drains the rest of the parrallel connected cells, it should be replaced, or earlier if it’s efficiency drops significantly. In the first case, I should be able to detect an increase in temperature relative to it’s neighbors. So I could use thermal camara/sensor to see which cells are the hottest while the pack is idle and the dead cell is draining the other cells. Or when the pack is charging, the cell is taking current but not actually charging much, thus the energy should be lost in heat? (again detectable by temperature). Or thirdly, when discharging, the cell is barely contributing any current and will actually be colder in temperature?
Ofcourse I could measure the current going out and remove cells that contribute little to no current, but that would require significant cost and/or effort.
Which of these methods do you guys think is the best/easiest/reliable to detect a cell that should be removed, or do you have any other suggestion?