Here is a comparison of 2 individual cells in a 5 cell 5Ah 20C LiPo pack being used on my electric strimmer, therefore they were both subjected the exact same load:
The the
blue cell is still performing reasonably well for its age but the
red cell is much weaker and the additional voltage drop under load is very noticeable.
The voltage difference at the beginning of the test was ~0.02V, and at the end of the test under no load it was ~0.05V.
Under light load, the difference between the two cells was ~0.05V, but at peak load, the difference was over 0.55V.
If we look at your results, it appears that your cells are not under sufficient load to produce anywhere near the
0.45 and
1.03V voltage drop that my cells experienced under heavy load:
If you haven't reduced the Maximum Current setting of the Magic Pie, it will typically draw ~25 Amps of current
(~1,300 Watts @ 52.5V) under heavy load at low speed.
If your cutting out problem only occurs under heavy load, it is likely that the test loads you are using are not enough to reproduce the problem.
I suspect that if you left your motor running with just your treadmill motor and bulbs as a load, it would continue to discharge the battery well below 50V before it would cut out.
As your cutting out problem is obviously related to load, either something is unable to supply the required current
(e.g. weak cells or a poor connection on one or more of their interconnecting links) or possibly a problem with a balance lead connection
(or the BMS unit itself).
Alan
