lifepo4 cell group reverses voltage?

joe tomten

100 W
Joined
May 13, 2009
Messages
211
Location
E. Mass., U.S.A.
Just hauled out one of my bikes that has a 12s lifepo4 battery connected to a signal lab bms (red blinkey led type).

The first cell group is MINUS 1.5v, and all the others around Positive 3.2 - 3.3 v.

how can this happen?
 
Can we have more infro as what type lifpo4 ?Wwhere do you get the battery ? How old ? Ect.
You need to cut the string of bad cells. To save the rest.
 
no way to know how you measured, but if you leave it plugged into the controller and allow the battery to drain down totally into the controller then the lowest cells can be reversed by the higher cells forcing current through it. usually they blow up and get hard then.
 
generic 26650's i got used a couple of years ago. been good in service. not high c cells.

Yes, will have to cut in a new parallell group. I put this pack together from other funky packs - so this isn't new. Just a pain.

i didn't leave the controller on. cell groups 2 . . 16 remained nearly fully charged.

can a signal lab bms slowly bring cell group one down to zero if the balance cable is left plugged in? Seem to remember something like that.
 
Yes, unplug bms's for storage. One reason I don't like "canned" batteries that more or less prevent this simple and well known precaution.
 
thanks dogman,

chagrined i am to be told "well known" when i was hoping "merely suspected"

Time to reconfigure all my balance leads to some varient of Dr. BASS's db25 balance connector situation.
 
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