Battery Health numbers

[ChrisW]

Hi,

I've been running a second-hand E-bike for 7 months. The battery had no BMS and was charged (not balance charged) using a power brick. It's a 24V system, the battery was homemade and is 7S5P. I've just stripped it down and can report that, when charged, the cell banks show 4, 3.9, 4, 4, 4.1, 3.9 & 4.1 volts. The internal resistances vary from 16 to 30 milli Ohms. I guess the voltage variations mean that the pack is 0.5 volts lower than a properly-balanced pack. I suppose this means the charger will plough on to it's 28.7 target at the expense of over-charging some of the cell banks, which is a Bad Thing. I don't know what the impact of the differing internals resistances is though. I read that this parameter is a measure of cell health - higher being worse.

I have now installed balance leads and a centre tap, and will in future, balance the battery in two halves (lower 4 and upper 3 cell banks) using my B6 mini. I don't know if I'll do this every time, or just when-needed - I guess I'll feel my way.

If I have anything wrong above, or there's anything you can add, I'd appreciate your corrections and comments.

Thanks,
Chris

 

[Deleted member 4366]

You should never run a lithium battery without either balance charging or a BMS. When they catch fire, there's no stopping them. I've seen them go off twice when a cell got over-charged. They were massive explosions, like a shotgun being fired.

 

[ChrisW]

Thanks for the that.