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Discussion Starter #201
...Given voltages mentioned in this patent, it makes me think it's possible, or likely, that when a cell dips below say 1.1V, it might degrade the 'cobalt conductive matrix'. And since, in the car, there's never anything approaching a re-formation type of charge, that cobalt is lost. Self discharge and the cell's ability to cope with future incursions below 1.1V will erode the cobalt matrix even more. Eventually you end up with a cell or more with super fast self discharge and a failed pack... At least, that's my vague theory...
This statement makes it sound too much like I'm concerned about minor 'blips' below 1.1V. That's not the case. There's really two main things I'd be worried about:

-in connection with what I've learned from 'rock-bottom' charge state usage and taking tap measurements (such as the charts strewn along in above posts), I'm concerned that 'the car' doesn't actually catch cells all the time when they drop well below 1.1V.

-uneven self discharge: it's what makes risk to single cells all the more likely.

My concern is that it may be all-too easy for a single cell to be regularly, perpetually driven low. There's two 'bad' things that I'm thinking result from this (beyond the already-too-fast self discharge):

-the cells that remain high get voltage depressed; they need to be discharged down to at least 1.1V. The one low cell disables the discharge before these other cells get even close to 1.1V.

-the one low cell gets driven below 1V on a regular basis; the new idea is that this might damage the 'cobalt matrix', and this damage would result in smaller capacity, lower efficiency (i.e. worse performance), but most importantly, even faster self discharge and even less ability to cope with this kind of abuse.
 

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-the one low cell gets driven below 1V on a regular basis; the new idea is that this might damage the 'cobalt matrix', and this damage would result in smaller capacity, lower efficiency (i.e. worse performance), but most importantly, even faster self discharge and even less ability to cope with this kind of abuse.
We knew this general principle (maybe not the names or exact technicalities) from years of owners anecdotal evidence. Thanks for fleshing it out.

Once a pack throws codes if you do nothing other than reset it (punishing the weak cells) then it's inevitable demise usually follows.
 

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One other thing I should probably add here. One of the long-lived factoids at IC says the BCM won't let you discharge the pack all the way. The common thing to say is that 'the BCM allows pack usage between about 20% and 80%.' I won't dig into the weeds with this (I could), but rather, let me merely point out that, with an OBDIIC&C, using the SoC reset function, you can drain the pack to pretty much truly empty. In all these years I never quite realized that was possible, until now. The '144V rebound thing' seems to be a tell-tale sign.

Even without the OBDIIC&C/resetting SoC, you can drain the pack completely, just that it takes a lot more work because you have to fight the nominal-SoC-triggered throttling behavior and either use the Calpod IMA disable switch repeatedly, to disable regen and background charge, or do some fancy shifting into neutral. Also, I should point out that it appears some BCMs do allow full discharge as a matter of course, such as the A03 I might've mentioned some posts up.
I have a soc reset box and try tricking the ima to full ,it does work but when I disable the ima with the calpod switch I still see the 4 bars of regen,so it’s hard to get it to drain down.
 

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Discussion Starter #205
Eq1is there a Udd thread post you started about discharging with the paperclips,,I sent you a conversation,,,thank you,
Here's a post, in this thread, that briefly documents the process: The quintessential Insight NiMH voltage thread

Here's a link to a thread where I reexplained the process and helped someone work through it. I think that starts some time after the first few volleys of exchanges, somewhere down the thread:

My methods are always slightly evolving, but I think the gist of it remains the same as what's explained in these locations.

I have a soc reset box and try tricking the ima to full ,it does work but when I disable the ima with the calpod switch I still see the 4 bars of regen,so it’s hard to get it to drain down.
I think there might be two major 'kinds' of background charge/ICE charging, one that the Calpod switch can typically disable, the other it can't, or at least has a harder time doing it. The latter is the same or akin to the 'forced charge' or '4 bar mandatory charge' that happens after a bonafide neg recal. I think once the pack is truly near empty (or if a cell is near empty), the BCM detects that and thereafter the background charge becomes much harder to disable with the Calpod, even if you have an OBDIIC&C or 'reset device' and reset state of charge high.

Since I now routinely use my pack at low charge state, and I've been experimenting with draining it almost completely everyday, I'm often struggling to control the IMA with the Calpod - it just doesn't work as reliably 'down there'. I often have to hit it twice or more, or at just the right time to get it to work. It's weird. It's like the clutch switch check in the 'algorithm' happens at a certain time in a sequence of checks, and once the pack is truly low it just doesn't check as often - like it forgets that it's supposed to check for the clutch switch - but, once in a while, it still does...
 

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After reading both the 1449 post and this one, you seem not as sure about the Udd method now as you was at the start, you highlight the need to really monitor the last 3 to 5 hours of the charge ,would you say this method is for the more advanced than the average method of charge and discharge we see on ic here. Also why would this method not work on non factory packs.
 

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Discussion Starter #207
After reading both the 1449 post and this one, you seem not as sure about the Udd method now as you was at the start...
That's probably true in the sense that originally I thought it was highly unlikely-to-impossible to damage cells with this method, and now I'm not totally sure. And originally I thought it was possible that taking a cell below 0.25V was actually a part of the reconditioning, that a certain reaction probably happens and helps, but now I... kind of doubt it.

But in general it's still a lot better than working with a full pack.

you highlight the need to really monitor the last 3 to 5 hours of the charge
Generally anybody grid charging should do that. If you want to be careful you do it, otherwise you do whatever you have time for, whatever you care to do... There might be some subtle differences grid charging after a thorough ultra-deep discharge vs. any other time that would make it prudent to monitor the end of charge more closely; after an ultra-deep discharge, the end of charge voltages will be higher, there appears to be reconditioning that happens that results in higher voltages than usual. So, if you want to better gauge if what you've done is likely to have been effective, then you'd probably watch the end of charge...

would you say this method is for the more advanced than the average method of charge and discharge we see on ic here.
More advanced? In the sense that sticking paper clips in terminals and causing shorts seems like a radical thing, seems weird compared to 'discharging with a light bulb' and 'doing cycles', yeah, it might seem like an 'advanced' thing to do for a lay person, I guess. But it's really just a natural extension of full pack methods, but a better, more thorough, safer, etc. approach. Full pack methods and cycles are a very blunt and risky approach. Tap-level is way less risky and in some sense easier, as you don't have to fuss with changing light bulbs, worry about multiple voltage levels, etc.

The main thing is that full pack risks reversing individual cells for long periods and at relatively high discharge rates; tap-level reduces that risk by a couple orders of magnitude, in a couple different ways. You reduce the series from 120 cells to 12, and you have a load that's a tenth the size.

Also why would this method not work on non factory packs.
My understanding is that aftermarket cells have a slightly different formulation and do not respond favorably to deep discharges. Or the flip side: OEM cells seem to have a special formulation that allows them to be deep discharged not only without damage, but with potential benefits.
 

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Well first attempt went not so well ,got the pins in right place around lunch time,20 mins later went to start car,and the 12 volt battery on and almost drain the battery that fast,what am I missing,I have the calpod switch in disable and ima pack on or off didnt make a change,,glad I wasnt far away anywhere,at work so it started of starter which I'd expect with bcm unhooked. Fill me in,do I need to just park the car for 2 weeks and unhook 12 volt battery..that would suck.
 

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First 5 taps finished at 4 days now moving to 2nd set of taps. No problom driving the car today to work after sitting all weekend. Bcm unhooked on both sides,starts off starter and no 12 volt drain on battery. So far so good. Am following 4 straight days of tap drain this first time around..
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Discussion Starter #213
Here's a link to some contemporary 'voltage' analysis of someone's pack (cells), some new graphs, data, etc. Includes cell-level self discharge data and cell voltages after a couple grid charges...
 
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