LEAFSPY RECORDING OF HILLCLIMB 2
First section (0 to 1min 40sec)
I have to admit to some surprise on what I saw on the recording, especially at 22 seconds (the highest load, at 177amps). No surprise with #29 doing its dive, but #53 doing an even bigger dive to just 10mV above #29 and a couple of smaller but notable dives by #78 and #96. So using the cell voltages at 0 seconds as a no-load reference, the dives were #29 did 324mV, #53 did 400mV and the cellpack average dived 190mV. A little later, say at 50 seconds, when the car has stopped, #59 has returned to a middling position within the 94 'good' cellpairs.
Several thoughts occur to me about this behavior. At first glance, it looks as though there is not much point in trying to improve the delta-V of #29 by any more than 10mV from here because #53 would then become the defining cellpair for a low battery warning. Next, I'm puzzling about #59's behavior. It appears to have adequate capacity given its relative voltage position among the good cellpairs but is suffering from excessive internal resistance, as shown by the large voltage dive. IMHO I think it's quite unusual for a lithium cell to have good capacity, yet high internal resistance, which leads me to believe there might be an issue with the connection of #59 to the busbar, such as an under-torqued cellpair terminal bolt or even an over-torqued bolt which might damage the busbar conductor - after all, it only needs an increase of 1 MILLIOHM over the desired resistance to cause a 177mV volt-drop at 177 amps. WHATEVER THE REASON, MY EXPERIMENT CAN DO NOTHING TO IMPROVE THIS BEHAVIOR, AS THE BMS SEES NO DELTA-V ON #59 TO BALANCE.
Second section (1min 40 sec to 4min)
The second section is a shallower version of the first section due to it being less steep and I was traffic limited to about 45 mph. This time #59 got no closer than about 40mV above #29 at a lower load of 154A (1min 48sec), though #29 continued to show a smaller volt-drop (no-load - load volts) than #53 of 310mV and 350mV, respectively.
Third section (4min to 5min 8sec)
During about the last quarter mile of the third section, I took the opportunity to speed-up due to the absence of traffic. The speed limit was 45 mph and all I'll say is I went well beyond my comfort zone (the speed pointer disappears behind the display hood during the last 30 or so seconds of the video!)...still no range 'dance' nor low battery warning. I think the low point for #29 is 3.273V and its delta- V peaked at 320mV (at 3min 48sec). This was the only time that the volt-drop of #29 exceeded that of #53 (590mV versus 480mV)
Conclusions: Despite the surprise behavior of cellpair #53, I think #29 remains the main limiter of further improvement because #53 only got close to #29 at the beginning of the climb. In the near future, there may come a point where #53 will be the lowest cellpair, with further reduction in the delta of #29 but I think this will only happen at high SOC and high load, so it won't have much, if any, effect on the car's range or SOC.
I continue with reducing the delta-V of #29 and in the meantime, may also do a leafspy recording at a lower SOC (say 50% SOC), just to confirm that #29 is still the main block to further improvement.