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....I think you must be very careful using pack voltage as some sort of indicator of pack condition. It is generally felt, I think, that bad packs plateau at higher voltages while good packs plateau at lower voltages. .....
Hi,

I wanted to chime in on what Jim said above.

Mike D has consistently said the same thing:

Good, strong packs, peak at a lower voltage.

Weak packs peak at a higher voltage.

This is important, thus my saying this a second time here....


Jim.
 

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I haven't read the whole thread yet, but I wanted to address the title of the post - "Do Stored Sticks Improve w/ Age?"

The answer is no, they continue to deteriorate at 1-2% per year depending on storage conditions.

Self-discharge balancing is another matter.
 

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You are a pro. It is likely folly to argue with you; however, the operative word is "improve." In this scenario, "improve" means to perform better. The question wasn't if NiMH cells improve during storage. I feel that's the question you answered, not the subject of the post.

Then the question becomes, does self-discharge balancing improve stick performance?

If that's the criteria that actually shows the improvement, then based on my experience with the pack that self-discharged for 2.5 years, I have to say yes.

So if we rephrase the question as, does self-discharge balancing during extended storage improve stick performance in their intended application? The answer is yes in my experience.

Steve
 

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Can't disagree! But 2.5 years is an awful long time to wait for your sticks to balance themselves... :D
 

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Can't disagree! But 2.5 years is an awful long time to wait for your sticks to balance themselves... :D
For the typical owner, absolutely. I have 4 packs for 2 cars, so... :)
 

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Interesting thread.
One of our members bought all my old sticks, many of which had sat for 3-4 years. Some of the sticks came from hybrid battery repair, some from packs I repaired with new cells.
He has run all of them through a reconditioning process, and the last I spoke with him, he indicated that many of the sticks were in decent condition.
http://99mpg.com/blog/whatactuallygoeswr/someseriousworkahe/


The first gen Prius cells that are at least 10 years old, are now powering my EV telephone truck, and EV yard buggy as well as the EV minibike.
They are configured as 7 cell modules, and I have 4-8 of the modules in parallel when using the yard buggy for extended periods.
I was skeptical about using so many modules in parallel, but so far so good.

Final issue is the juice in the cells.
It is a concentrated Potassium Hydroxide fluid.
New cells have several drops of extra liquid,and the inter plate separators are well saturated, but all the old used cells that I have dissected are pretty dry, and show sections of blackened very dry separators.

You may remember my reporting on the fire issue with the new cells.

I had one new cell, that I opened, then rinsed with tap water before unrolling the plates and separators on my work bench outside.
I went in to further rinse the slippery Potassium Hydroxide off my hands, and to neutralize it with vinegar, and when I went back out to photograph the plates, I found to my surprise that the plates were on fire, and had spontaneously ignited.
The water I had used to rinse the cell core while still rolled up, had reacted with the hydroxide, and spontaneously ignited.

It is great to see so many people that have benefited from grid charging and reconditioning their packs.
 

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....Final issue is the juice in the cells.
It is a concentrated Potassium Hydroxide fluid. New cells have several drops of extra liquid, and the inter plate separators are well saturated, but all the old used cells that I have dissected are pretty dry, and show sections of blackened very dry separators....
Great information. I had been wondering what exactly the electrolyte looks like - and imagining, erroneously, that it was a free flowing liquid inside the cells. But then, I had been examining some picts at your website of disassembled cells, and now your summary above: saturated separators with "several drops of extra liquid" in new cells; old cells "pretty dry"... Now I shouldn't have to cut open any batteries, at least for now...

One other thing I wanted to mention, after re-reading a bit of this thread. It has to do with 'how low do you go?', the difference, if any, between a battery drained via prolonged self-discharge vs. a manual 'super' deep discharge, etc. Of course I don't know anything along these lines for sure, and I'm no electrochemistry expert, not even close. BUT, my hunch is that it shouldn't matter what means are used to get cell voltages low, as long as all cells DO get low.

I think that's the critical difference: most of the manual discharges have been at relatively higher rates (i.e. relative to the rate of a self-discharge), on multiple cells in series, and usually not to very low voltages. The result is that not all cells reach the critical low voltage threshold - so not all cells get 'fixed', and performance doesn't bounce back as you'd expect or want. But a prolonged self-discharge DOES drain all the cells to that critical low threshold (I'm thinking 0.19V-0.78V per cell, yet really interpreting the research as indicating 0.19V, all else being equal).

Point is, based on my reading, once you see that critical voltage, it indicates that this or that 'phase' is gone - it's like a chemical, scientific fact: you see this or that potential/voltage because this or that chemistry is going on; if you don't see this or that voltage then this or that chemistry is no longer happening. So, I don't think it matters how the cells get low, so long as they get low. I mean, it matters for other reasons - like you wouldn't use a 50A load to take 120 cells down to 0 volts. But it doesn't, or shouldn't, matter in terms of getting rid of voltage depression, as I understand it...

One aspect that remains a bit unclear to me is the variation one might see in the real-world vs. the technical/theoretical values. For example, I'm using 0.19V-0.78V based on my interpretation of stuff in that book. And then, I saw about 0.63V for each cell in those sticks that sat for a year. And Keith saw similar values. Of course there will be variation based on measuring instruments; that's not really what I'm concerned about.

I'm concerned about the meaning of that range between, say, 0V and 0.78V. In my limited experience it has seemed as though there's very little difference, capacity-wise, performance-wise, functionally, between say 0.63V and zero. For example, you stick a 75w bulb on a pack with all the cells at 0.63V or zero, and in either case the bulb is going to be dark or go dark in seconds. The extent to which it doesn't simply reflects the extent to which some cells are not discharged as much...

Point is, there's wiggle room in these numbers - such as 0.19V per cell - when it comes to the realities of doing the work, discharging the packs or sticks or individual cells, measuring, etc... The technical/theoretical value is cut and dried - or it is in the sense that, if we've picked the right number, by nature it is cut and dried; generalizing that value to the work we have to do is a bit different.

If, for example, that critical threshold IS 0.19V, how do you ensure that each cell in a 120 cell series reaches it (barring 120 DVMs)? It seems like, you can only be sure if you take the pack to zero...

Anyway, I think I mentioned before that the great task seems to just boil down to discharging the pack or stick or whatever more or less completely. Light bulbs, fixed watt resistors - things that complete the task with lower and lower currents the lower the state of charge gets, seem to do it, seem to be the way to go. You try to limit the number and duration of cell reversals as much as possible, by whatever means; the lower the pack gets the less deeply reversed cells will be driven; etc. etc...
 

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Discussion Starter #28 (Edited)
One other thing I wanted to mention, after re-reading a bit of this thread. It has to do with 'how low do you go?', the difference, if any, between a battery drained via prolonged self-discharge vs. a manual 'super' deep discharge, etc. Of course I don't know anything along these lines for sure, and I'm no electrochemistry expert, not even close. BUT, my hunch is that it shouldn't matter what means are used to get cell voltages low, as long as all cells DO get low.
I don't know much either, but I did take chemistry classes in college;)

It seems to me that there might be some molecular mobility issues between the two techniques. In a liquid, one usually sees some churning or swirling going on during a reaction. In a paste, like we have in the cells, one can speculate that the mobility of new chemical compounds is considerably slower and requires time to achieve their full effect. It isn't even a theory, just speculating.

I think that's the critical difference: most of the manual discharges have been at relatively higher rates (i.e. relative to the rate of a self-discharge), on multiple cells in series, and usually not to very low voltages. The result is that not all cells reach the critical low voltage threshold - so not all cells get 'fixed', and performance doesn't bounce back as you'd expect or want. But a prolonged self-discharge DOES drain all the cells to that critical low threshold (I'm thinking 0.19V-0.78V per cell, yet really interpreting the research as indicating 0.19V, all else being equal).
I don't think it is really necessary that ALL cells get fixed or need to be fixed. Having looked at a ton of cells, I'm convinced that the "bad" cells amount to only 1 or 2 per stick, on a statistical basis. The "good" cells, the ones which retain high voltages after the stick is exhausted by the "bad" cells don't need to be fixed.;)

One aspect that remains a bit unclear to me is the variation one might see in the real-world vs. the technical/theoretical values. For example, I'm using 0.19V-0.78V based on my interpretation of stuff in that book. And then, I saw about 0.63V for each cell in those sticks that sat for a year. And Keith saw similar values. Of course there will be variation based on measuring instruments; that's not really what I'm concerned about.
I think that there is a big complication with doing the deep discharge at a pack level, if one tries to think of what the individual cells are doing. Your book, and I have no complaint about the book, discusses things at the cell level. We have 120 cells in series, so those rejuvenation processes possible at the cell level are not possible at the pack level. A logic different other than "cell logic" is needed. Mike D. has offered on, successive discharge level.

I'm concerned about the meaning of that range between, say, 0V and 0.78V. In my limited experience it has seemed as though there's very little difference, capacity-wise, performance-wise, functionally, between say 0.63V and zero. For example, you stick a 75w bulb on a pack with all the cells at 0.63V or zero, and in either case the bulb is going to be dark or go dark in seconds. The extent to which it doesn't simply reflects the extent to which some cells are not discharged as much...

If, for example, that critical threshold IS 0.19V, how do you ensure that each cell in a 120 cell series reaches it (barring 120 DVMs)? It seems like, you can only be sure if you take the pack to zero
You can't "ensure" anything about "each cell" when you are working at the pack level. In fact, you can't even "ensure" anything about "each cell" when working at the stick level. (Hit a stick with a 10A discharge from your Superbrain, and watch each cell voltage. You will see that the capacity of the stick is most likely dictated by 1 or 2 "bad" cells. Envision that problem x20.)

Mike's apparent philosophy (I hate to convey my feeble understanding, perhaps he will correct me is I'm wrong.) is that PACK discharging at successive lower levels, as provided by Version 3.0 of the Genesis S/W,
"heals" the weakest cells first, and the next weakest cells next, and so on. All known evidence, including his testimony, indicates that this method provides "some" relief for failing packs. Even this beneficial procedure isn't claimed as a permanent fix - maybe a year or two.

The number of folks who work at the stick level is very low. In the Mid-Atlantic crowd I'm pretty sure that I am the only one doing any of that. Perhaps cell and stick level investigation sheds a little light on the various phenomenon, but it is entirely too time consuming for any but the OC types(me, you, keith, d dude, maybe Eli) ;)
 

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IMHO...

After doing a series of charge/discharges at the pack level, and seeing positive results, I thought it would suffice to start working at the stick level to get some real improvement. I was wrong.

All real improvement at any level is had by improvements at the cell level and not looking at the cell level is just making guesses and/or getting lucky. I'm going to read over Mike D's cell level efforts and formulate a plan. DimensionDude's setup is cheap and elegant in its simplicity, and I plan to utilize something similar tweaked for cell discharge.

Again, only IMHO. YMMV :)
 

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The batteries in the car have a level of abuse that is widely variable, which is why i took a new Bumblebee stick, cut the cells apart, and have carefully reverse charged 2 of them.

I am cycling one of the abused and one of the the not abused cells in series in a test load of 15A to see if I can detect any long term difference. After 50 or more cycles, the single 2A totally reversed cell (saw - 1.8V at the end of the reversal) is still behaving virtually the same as the not reversed cells, with the only difference being that it charges to and settles to a slightly higher voltage than the not reversed cells.
If EQ1 or anyone else that wants some single new cells to test, and do a more scientific test , I believe I have 5 more of the new cells that have never been used.
 

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Discussion Starter #31 (Edited)
IMHO...

After doing a series of charge/discharges at the pack level, and seeing positive results, I thought it would suffice to start working at the stick level to get some real improvement. I was wrong.
Yeah, that is the argument I was kinda making. Anything more than cell level is just kinda a dice roll. Yet, you and others reported some improvement at the pack level. I'll join you in the cell level stuff, as time permits. Maybe we will learn something.

All real improvement at any level is had by improvements at the cell level and not looking at the cell level is just making guesses and/or getting lucky. I'm going to read over Mike D's cell level efforts and formulate a plan. DimensionDude's setup is cheap and elegant in its simplicity, and I plan to utilize something similar tweaked for cell discharge.

Again, only IMHO. YMMV :)
Mike D's work is certainly a touchstone to start with. In fact, he may get to the actual cell level answer :)

If you want to be OC(like me and others) on wringing out another year of performance, you are "probably" on the right track. DimensionalDude's setup relied on the Harbor Freight batter testor, while probably ok for its intended purpose, it doesn't serve very well for these kinds of experiments. It isn't very stable and timing with it is very imprecise, unless you use a relay for off/on. I've evolved from that first device, which I originally copied exactly. I need to figure out how to post pictures of my current setup, evolved as it if from his first efforts.

Rather than buy the Harbor Freight Carbon Pile, with its associated problems, I would opt for some nichrome ribbon from eBay - cheaper and more stable. This is the load material that Mike uses.

nichrome ribbon | eBay

Ribbon has an advantage over wire in that the added surface area keeps the ribbon cooler and more linear.

Just ideas to kick around.
 

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Discussion Starter #32 (Edited)
I am cycling one of the abused and one of the the not abused cells in series in a test load of 15A to see if I can detect any long term difference. After 50 or more cycles, the single 2A totally reversed cell (saw - 1.8V at the end of the reversal) is still behaving virtually the same as the not reversed cells, with the only difference being that it charges to and settles to a slightly higher voltage than the not reversed cells.
To me, the elevated voltage would indicate that there is some unknow level of damage. Many cycles would be needed to demonstrate whether the actual useful life of the cell has been affected. A car goes through hundreds, perhaps thousands of cycles during the life of a battery. I hope you are doing this cycling with automated controls, as I suspect;)
 

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My test is simple,and not very precise, which is why, It will yield better results if duplicated with instrumentation.
I started the test back when we first began trying deep discharging, and was mainly to compare a reversed cell and a non reversed cell to see what differences there were right after the reversal and see if any develop with cycling.

I have not automated or instrumented the test, and mainly look at the run time under the ~15A load, and see which cell drops out first.

I have stopped running the cycles, as I do not feel I have any more to learn from the test, and don't expect to be setting up a more accurate test as I am flat out on so many other projects.
 

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Discussion Starter #34 (Edited)
Thanks Mike for your honesty - as always!

I would ask for the cells, but I don't see myself doing the work either. It seems to me that automation and some understanding of accelerated testing would be required to measure the full impact. By "accelerated" I'm thinking that maybe stressing the cells to use perhaps 80% capacity would be a defensible measure. Even then, statistics come into play and one example would be contestable.

Time is already too short :(
 

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I too would love to get my grubby little mitts on individual cells, but the reality is my contribution would add nothing to the greater good. :)

I am encouraged by the more-than-anecdotal results Mike presented in this thread concerning forced reversal and charging, and it has given me some ideas for experimentation.
 
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