Originally Posted by david85
The high voltage cutoff is taken care of my the charger since it dynamically adjusts the charge current and voltage during charging and will shut down when charge is complete, so in effect there is a high voltage cutoff. The high voltage failure of the cell is claimed to be over 10 volts, the charger stops charging at 3.65V (my observations show closer to 3.55V, but its cool outside right now). The low safe voltage is 2.5V, this is considered the 100% DOD mark.
From my observations, there is a significant drop in amps (~25%) by the time you reach that point. There are low voltage alarms that EVs can be fitted with off the shelf, and I don't think it would be hard to adapt an actual low voltage shut off that will disable the main pack if some one is careless in operating the vehicle.
I don't really see the problem with the charger mouted BMS. The 4 cell ballancer that my sample uses seems to work just fine. Seems to me its fewer thigs to go wrong. The ballance time takes about 2 hours after most of the charge has been completed.
There are numerous issues with that kind of charging when multiple cells are introduced. Firstly Lions should be kept over 30% charge at all times unless you want to basically waste the battery.... one slip up where 1 cell drains faster than the next cell and blamo... loss of 16k dollars.
2ndly the overcharge might not happen, but bloating the batteries isn't necessary to hasten their life span significantly. Simply doing a 101% charge can kill the DoD by quite a lot.
Again you need cell to cell regulation and cut off abilities so cell voltages are monitored and kept from dropping too low for LIFETIME safety.