2001 5S "Turbo"
"Balanced" or "equal"?
Indeed. Yet, I was also thinking that most of the stick voltages are so similar that a value about 0.1V lower could be a tip-off... Problem is, I don't think the typical pack has such similar voltages, plus, it's really only obvious when you see all the cell voltages, plus, if anything, we usually only look at tap voltages. So, yeah, really hard to get anywhere just looking at aggregates.That shows the importance of cell level work which is even more time consuming and tricky than stick level!! I def need to build my semi automated stick tester. It's been discussed lots of times. I even have a schematic somewhere...
Yeah, I think single high self discharge cells is probably one of the main reasons for failed rebuilds. Unless you look at the cell level, it'd be hard to spot. I didn't start looking at cell level with respect to self discharge until late in the game (a few years ago), and even then I still gave it short shrift. I think the main reason we didn't pay enough attention is because we didn't fully appreciate that voltage alone can indicate HSD; you don't need to discharge the cells, but you do need to look at the voltages.......You may have touched on the reason folks have such poor success with rebuilding efforts. I have done a lot of cell level qualification based of heavy test currents and high indicated internal resistance(IR), but even that did not insure good packs. Looks like I may have overlooked the importance of self discharge(SD). One has to be impressed with how uniformly "good" cells are in their SD rates.
I haven't worked with enough packs to really know. I think HSD is probably the kiss of death for most packs. For high IR and capacity issues the car seems to be able to work with those, where failure will only be gradual, or where you can actually alter your driving behavior or putz with the OEM management to make things work. But with high self discharge - there's a threshold beyond which you'll never be able to use the pack.Of the three major parameters, IR, self discharge, and capacity what is your ranking of defect likelihood?
As I recall it's based on thermodynamic calculations of the active materials of the cell - the potential difference (i.e. voltage) you calculate based on negative electrode stuff and positive electrode stuff. This 1.318V value though is something I saw in I think that 'Civic' battery research paper that's been around IC for ages*... What's fascinating is just how close a lot of my cell voltage readings are to this value... "Equilibrium" conditions in this context is what the battery folks call anything other than charging or discharging, it's similar to "resting voltage," only a resting voltage that'd be measured under ideal circumstances, such as a new cell, half charged, 25C temp, etc. I think it's also an antonym of "transient" conditions, where charging and discharging are considered transient...I'm a bit confused by the term "equilibrium voltage." How do you define this term?
....All the sticks were more or less conditioned, balanced, and left at about 73% charge state 33 days ago. Most of the cells still should be at around 70% charge state. The red-ish highlighted cells are ones with high self discharge (HSD) - they likely have very little charge left in them. Most of the sticks with these cells won't work, they'll cause any pack they're in to fail. Stick 50 for sure, probably stick 37, and 45 and 41 will cause problems eventually. The yellow highlighted cells are questionable. Sticks 71 to 74 at the bottom come from a different pack, which is why voltages are slightly different. All the sticks are 2007 Civics, though.
Was just thinking about this last caveat. I'm trying to conceptualize whether it matters what current the discharge is happening at -- I'm thinking it doesn't matter. Based on observations while driving it doesn't look like there'd be a difference. If I'm humming along at say 20-30 amp discharge, the BCM will detect a near empty cell at a charge state maybe about 5% higher than it does at 1.1 amp autostop discharge. I'm trying to wrap my brain around the actual calculation taking place, or maybe not 'the calculation' but its impact/effect.......I estimate that the 'slope detection algorithm' is able to stop the discharge when a cell drops to about 1.0V - at least at this low discharge current.
The horizontal lines correspond to the 'cell1-6' values, voltage. There are no horizontal lines for the other variables. Each colored curve represents pairs of cells.observing the graphs plotted horizontal lines is a bit confusing to say the least. I'm not sure why the graphs are plotted the way they are, put trying to visualize along the horizontals is an exercise.
Reading between your lines, yeah, this is mainly what the graphs were supposed to illustrate.I see what I believe you / eq1 are looking at as far as the individual cells in the 6 cell sticks and how they drop off in separate curves at different rates during the drop off as shown in the second graph when comparing it with graph 1 and 3. And if this is the only indication being looked at in this stick of 6 cells than that should be obvious to anyone looking at the three graphs.
The only discrepancy is the cell voltage axis in graph 3, which has a lower bottom value. In this context it's negligible. You can compare the 10 minute mark voltage values, for instance, and see that graph 2 is about 0.1V lower than graph 3...The things I'm looking at are what the other parts of the graph are showing and how they get plotted....The thing is the graphs are not drawn consistently on either the Capacity (mHa) scale and the Cell 1-6 scale on the right. It's not a very big difference and unless comparing the high discharge curve on the horizontal graph lines might not be noticeable....
fyi, the temp axis, black curve, shows temp for a single probe on one of the cells. fyi, all the labels are defaults in my logging/graphing software, it's too cumbersome and not important enough to make changes.Final thoughts: I'm glad the time and Int Est Temperature are consistent in the three graphs or I'd probably bee pulling out clumps of hair like with some other graphs I've seen with little or completely unknown definition(s) of axis' scales
I've been 'doing neg recals' like this for about a month now, with slightly different conditions some times, such as different tap voltages. Basically, I know I've got a relatively faster self-discharge cell in tap 7, and every time I've done this little test it all happens the same way. This last installment just happens to include some stark/extreme tap voltages/differences, but since it too has 'happened the same way', where Tap 7 has about the same voltage change at neg recal as the previous couple trials, for instance, it's pretty clear that those others parameters - low absolute voltage and tap-to-tap voltage differences - aren't the ones that cause the neg recal...Hmm.. What makes you so certain that it isn't your lowest voltage tap that is causing the negative recal?
What numbers of mine are you looking at? Lately I'm doing experimental stuff so most of the tap voltages I've posted aren't representative of what they'd 'normally' be. Plus, I've never looked at tap voltages under load (except for the meager few amp auto-stop variety)... Does "3 tenths" mean, like the difference between 14.5V and 14.8V? If so I'd say that's probably a bit bigger than the spreads I'd normally see, based on what I've seen working with sticks and cells and stuff...My battery taps are a lot tighter than what Eq1 is seeing. I've been monitoring my ten tap voltages as I drive. The taps are typically only 3 tenths or less from the highest tap voltage to the lowest...
Well, what I've described above suggests that most 'neg recals', bona fide neg recals, at least, are caused by a cell becoming empty before other cells, and that empty point is determined by the steepness of the tap voltage slope.I'm trying to figure out what the re-cal threshold might be as well. Based on Eq1's observations it looks like maybe a 3% voltage drop from the pack average. While driving, the biggest tap voltage differential I've seen usually occurs when the cells are being drawn down from load.