When is IR too much or too different?
I am flying my 450 helicopter with a set of 6 2.2A 3 cell 11.1V 30C Lipo Battery Packs which I monitor as carefully as possible. Post every flight I measure output voltage, IR of each cell, internal temperature and then I measure these same parameters pre and post charge.
This possibly seems a bit of an overkill but I am able to carefully see if any trends are occurring in any of my battery packs and I believe I have saved my helicopter exactly for this reason as one of my pack failed as I was spooling up the motor - as expected according to my recorded parameters.
I was expecting this failure because the one pack's IR different between the 3 cells was getting progressively further apart and progressively more. IR for the 3 new cells started of at 4,4,1 failed at 18,15,12. Knowing perilously little about battery electronics, I saw this as a sign of pending failure and I was, possibly by coincidence, correct.
But here is the real question.
If this parameter is as important as I think it is, How much difference between the 3 cells is too much? I am currently getting concerned when the max and minimum cell are 50% of each other. Is this too much or too little or am I barking up the totally incorrect tree here?