Originally Posted by
goingbush
It only takes one bad cell to pull down a whole pack , The cells don't degrade so much as they are not created equally. In service complete battery packs are discarded because of one cell . I have 45 x 200ah cells in mine and one is faulty from new, I estimate that cell has a real capacity of about 120 Ah so effectively brings the capacity of the entire pack down to 120ah I know this because my Battery Management System monitors the voltage of each cell , This one bad cell drops to 2.8V whilst the rest are on 3.1V From 2.8V there is a steep drop off to 2.6 from whence there is no recovery so I have my BMS shut the car down when the bad cell is at 2.8 .
As well as that one bad low cell , I have two cells that go high (I have BMS set to stop the charger when a cell reaches 4.5v) before the rest of the pack , so they fully charge before the others , thus again limiting the pack capacity. If you charge too high you can kill a cell, Thus a BMS is vital.
I have 4 new cells on the way from China , Rather than waste the bad cell I'll pick out the 4 worst cells and use them to make a 12v lithium pack for my caravan. Should last for ever.
Used Nissan Leaf packs are a really good way to go , only the low & high cells will be abused the rest will last another lifetime.
Bookmarks