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Do Stored Sticks Improve w/ Age?

7K views 34 replies 10 participants last post by  S Keith 
#1 ·
Hey, eq1. I think you may be on to something.

You made a remark in another thread, which I cannot locate, that you had some sticks that had been abandoned in a corner for a couple of years and that on retesting, you found that they had improved significantly.

I am having the same experience. I have about 10-12 sticks abandoned about 2 years ago, some of which are now testing fair-good. Is it just possible that something improves with long rest times and complete self discharge? Since we are dealing with chemistry, possible the dendrites or whatever goes wrong somehow dissolves with long rest time.

(I'll be happy to merge my comments into your thread if you will point me to it:))
 
#2 ·
I certainly think so. I mentioned buried in there somewhere that a HCH2 pack that sat for 2.5 years in the as-removed state showed similar results. The as-received pack voltage was 59.6V. All sticks came in at 5300-5500mAh, and there was no capacity improvement with cycling. The pack is performing very well in a car, but it's only been a few weeks.
 
#3 ·
Hydration

Dry cells are not "dry ". The water in the electrolyte is the medium which transports the ions The loss of water will render the cell useless. Mike has pointed out that failed cell are dried out at the electrodes. Venting dries out cells.

During use the water tends to be driven away from the higher resistance areas by the heat generated and it tends to accumulate in the cooler areas. Over years of non use (rest) the water distribution in the electrolyte (what remains of it) will tend to be equalized again.

Whether this is so could be determined by doing an ionization/conductivity test on a micro level throughout the electrolyte of deteriorated cells as compared to recovered cells. A direct measurement of the water content of the electrolyte at the micro level would be a more direct method. Either method is difficult to do.
 
#4 · (Edited)
Hey, eq1. I think you may be on to something. You made a remark in another thread, which I cannot locate, that you had some sticks that had been abandoned in a corner for a couple of years and that on retesting, you found that they had improved significantly....
I've peppered that around in various places, but the main place is the "impact of deep discharge" thread; the linked page below has the most of it:
http://www.insightcentral.net/forum...pact-deep-discharge-prior-grid-charge-10.html

I've been more or less working from the research conducted by some dude (Robert Huggins) at Stanford, who wrote a book titled "Advanced Batteries," debunking in one small section myth and conceptions about 'memory effect' in the positive nickel electrode. So, everything he explains seems to be consistent with what I've found; the problem that a deep (super deep) discharge fixes is 'memory effect' or 'voltage depression' - it's all about the electrochemistry. The voltage depression is caused by the formation of an 'amorphous' phase of nickel, hydrogen and oxygen during overcharge, and the way to get rid of this is to drop the voltage ("well") below that stuff's potential (0.78V). It just disappears upon recharge and the cell's capacity (and behavior) returns to normal.

It's always been a bit unclear to me, though, just how deep is necessary. The sticks sitting in my garage for a year were pretty much totally discharged - 0.63V per cell - so discharged that sticking the voltmeter probes on the stick would drop the voltage [edit: actually, it was the charger leads, not the DVM probes]. At one point I had been thinking that dropping voltage just below 0.78V, at whatever current, would be good enough, but I think it takes a bit more than that. I HAD done that, just below 0.78V, but I didn't see the radical improvement/transformation that I've seen - definitely in these totally self-discharged sticks - but also likely in a full pack I dropped to 22V as well as individual sticks for which I dropped each cell's voltage to something like 0.6V at 1.3A. This latter threshold still might not be enough, as the results on those 20 sticks seem to be a bit mixed...
 
#5 ·
It's always been a bit unclear to me, though, just how deep is necessary. The sticks sitting in my garage for a year were pretty much totally discharged - 0.63V per cell - so discharged that sticking the voltmeter probes on the stick would drop the voltage [edit: actually, it was the charger leads, not the DVM probes]. At one point I had been thinking that dropping voltage just below 0.78V, at whatever current, would be good enough, but I think it takes a bit more than that. I HAD done that, just below 0.78V, but I didn't see the radical improvement/transformation that I've seen - definitely in these totally self-discharged sticks - but also likely in a full pack I dropped to 22V as well as individual sticks for which I dropped each cell's voltage to something like 0.6V at 1.3A. This latter threshold still might not be enough, as the results on those 20 sticks seem to be a bit mixed...
I'm obviously confused also. I was frankly surprised at the improvement in sticks which had been given the "bad" call. Not all the sticks in that pile returned to operational status, but most did.

I had tried a progressive discharge to 0V in the case of a couple of other sticks, just by placing a 12 ohm resistor across the terminals. One of those sticks showed significant improvement, but the other was killed. I think that probably shows that there are multiple failure modes.
 
#6 ·
Maybe JimE you would be interested in my new toy? Its a smart battery charger for common house hold cells, aa, aaa, c and d.

I used it on all my solar lights. Some of the batteries it said right away were dead, others took a few hours to be declared dead, others were fully restored. The 3 solar lamps that showed water damage were dead right away. The few that had fallen over were considered dead after some cycles or attempted cycles. The rest were somewhat upright and worked for some length of time.
 
#10 ·
Hi I may have killed my Pack last night. I was discharging it with a 60w bulb from full. After 8-10 hrs it got to 147 volts. Then it took ~ 2 hrs to get to 140v. I went to sleep for 3 hrs thinking I will find it down to 130v . However after less than three hrs the bulb was dark and the pack was down to 1.8v!!! I left it bounce to ~14 volts and put on the charger. it went up to 50 volts in half a minute on the charger and in 10 hrs was up to 160v now 1s around 14 hrs of charge and it is up to 167.5v. I hope it can get back to 175 (it got to 172v on the initial charge) and behave OK. But also I am sure I inflicted some irreversible damage by bringing it down to 1.8v.....


Seems the described memory effect at 0.78v does not look like a big problem for NIMH batteries as my pack did not show much charge between 140v and 1.8v . at 200mA discharge it took it 2 hrs and 45 min total .
 
#11 ·
....Seems the described memory effect at 0.78v does not look like a big problem for NIMH batteries as my pack did not show much charge between 140v and 1.8v . at 200mA discharge it took it 2 hrs and 45 min total .
So, you're generalizing your one-shot results to all NiMH batteries? Seems a little odd. But in any event, if I understand the rest correctly, I'm not sure it works that way. Sounds like you're expecting a lot of capacity under 0.78V, is that right? If so, it kind of seems like that's the way it should work, that the capacity is 'all there' still; it's simply locked-in at a lower voltage than normally useful. But I haven't seen this in any of my tests, and it may be a misreading, misunderstanding, of the research...
 
#16 ·
Hi,thanks for the hope, and sorry for generalizing based on one accident .
The pack is looking good so far , it went back to 176.3 volts, after 20-25 hr recharge where before the "discharge" it stopped charging at 172.5 volts. Will drive with it today. I wanted to go to~120v as it was the first discharge, and eventually to go down to 80v - below the 0.78v described in the excerpt eq1 provided in the other thread on the deep discharge.
There the memory effect was described as shifting capacity under 0.78v with time. So the charge of an affected cell does not disappear it just remains hidden and unusable for the consumer at the second "Platoe " 0.78v .


I mentioned here because such a deep discharge resembles leaving the sticks aside for long time and the deep discharge that happens in those cases.
I had a pack that I assembled from old sticks after cycling them. 3-4 times each and the the pack sat for many months with the sticks disconnected. When I finally put I together it was at 118v. A full charge brought it up to 176.9 v . However I cannot see much how it performs as it is in my wife's cvt.
 
#17 · (Edited)
I mentioned here because such a deep discharge resembles leaving the sticks aside for long time and the deep discharge that happens in those cases.
Well, yes and no....
When the sticks self discharge on their own, they do that at very low current over a long time. The current used for most "active" means is much higher. I don't know that there is a difference, but it is perhaps worth noting.
I had a pack that I assembled from old sticks after cycling them. 3-4 times each and the the pack sat for many months with the sticks disconnected. When I finally put I together it was at 118v. A full charge brought it up to 176.9 v . However I cannot see much how it performs as it is in my wife's cvt.
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. The rest voltage, after some hours off the grid charger, may not be as clean an indicator.

As eq1 says, there is considerable lack of statistical rigor in all of this. We have multiple people, trying multiple techniques, on sticks of unknown multiple conditions. It is beginning to look like deep discharge really does improve things, as Mike has found out with his Genesis automated routines, but it doesn't seem to me that the exact mechanisms are yet know.

I have a kind of prejudice against doing it at the pack level, because I have a reluctance to "abuse" the good sticks within the pack, but perhaps time will show that this "threat" shouldn't really be a concern. I still do everything at the stick level, one factor being plenty of time on my hands;)
 
#22 ·
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.
 
#23 ·
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
 
#24 ·
Can't disagree! But 2.5 years is an awful long time to wait for your sticks to balance themselves... :D
 
#26 ·
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.
 
#27 ·
....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...
 
#29 ·
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 :)
 
#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.
 
#30 ·
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.
 
#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;)
 
#33 ·
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.
 
#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 :(
 
#35 ·
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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