Looks like this battery is shot .. I have been charging it really fully to try and get the bad cell to come back 5-6 times I "balanced" the cells ..This last time I let it go a little lower and it's cutting out at 54 volts where it was 52 volts it would cut out at a week or so ago ... If I fully charge the battery it will still easily do any ride I do 25 miles Max.
Don, it definitely sounds like you have at least one weak cell group whose voltage is dropping too low under load and causing the
BMS to cut the power.
If you look at the following chart you can see what happens to a
weak cell under load compared to a
good cell:
The good cell never drops below 3.55V, whereas the weak cell drops right down below 2.95V under the same load. You can also see that the poor cell's voltage quickly returns to 3.8V when not under load, and eventually settles at 3.95V after it has rested for a couple of minutes.
At the beginning of the test there was only ~10mV
(0.01V) difference between the good and the weak cells, and at the end of the test there was still only ~50mV difference (0.05V) between the two cells.
However, the difference between the two cells when placed under load is ~600mV
(0.6V) within 10 minutes of use.
I don't think your battery is completely
"shot" if it can still
"easily do" a 25 mile ride, but it is obviously on its way out if it's now cutting out at 54V
(~3.86V per cell).The
BMS cutoff voltage for individual cells
(or paralleled cell groups) is typically around 2.5~2.9V, therefore at least one of your cell groups is dropping at least 1V under load and causing the
BMS to cut the power.
Considering the huge increase in the number of electric vehicles in use today, you'd think there would be more individuals and businesses specialising in battery repairs.
If you continue to charge it fully before every ride
(right up to 58.8V) it will hopefully survive until you can obtain a replacement.
Alan
