"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.