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Discussion Starter #1
I didn't want to do a deep discharge on an unknown battery from the advice given here previously, so I did 2 shallow cycles down to 100V including a pre-charge using a Genesis One. These are the results. Seems pretty good compared to other batteries I've done. Should I do a third cycle like I usually do?

 

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Hmmm... discharge time INCREASED. Capacity gains result in a shorter discharge time as more capacity is burned at higher voltage, so you also get more current per minute. Your results are not indicative of substantial improvement.

Assuming you're using Mike's work lamp discharger, I would make a very crude estimate of 1.25A average. That's putting you at about 4.4Ah for the first and 5.1Ah for the second, but that would include capacity below 1V/cell, which is considered unusable.

Assuming you don't have cell or self-discharge issues, nothing stands out as negative.

Probably worth a 3rd. If you can time it, check taps at 144, 132 and 120V.
 

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Hmmm... discharge time INCREASED. Capacity gains result in a shorter discharge time as more capacity is burned at higher voltage, so you also get more current per minute. Your results are not indicative of substantial improvement.
If @atikovi is starting from the same higher voltage and ending at the same lower voltage for both rounds, and the load resistance is constant, and the source resistance is negligible compare to the load resistance, then the current at any particular voltage is constant on both cycles, and a longer discharge time can only mean a higher capacity...

V = IR
P = V*V/R

(and @atikovi, it sounds like you could continue doing cycles until you see the improvement between cycles flatten out - assuming there isn't something detrimental going on like a cell repeatedly reversing...)
 

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Discussion Starter #4
If I remember correctly, longer discharge time is better because it indicates greater capacity. More mAH and WtH charged indicate the pack can hold more power. That's my understanding from Mike's explanations but could be wrong. I do know the the packs I had with half those numbers, I needed to replace.
 

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You are missing a few things:

1) Input at 350mA isn't an indicator of capacity. It's how long the charger pushes current. I've pushed 25% more capacity into packs than the cycles you posted, and they yielded what they yielded independent of input (provided input exceeded what came out). The Genesis One has more advanced termination criteria, but I wouldn't regard it as an absolute.

2) Voltage depression (VD). It reduces capacity. Cycling eliminates this by consuming the capacity at the VD levels - below 1V/cell or 120V at the pack level. This is the purpose of grid charging and pack level discharging.

2a) You have X mAh of capacity at > 1.0V/cell and you have Y mAh of capacity at < 1.0V/cell (VD capacity). You improve X capacity by consuming X and Y capacities where X2 = X1 + Y (roughly).

3) Load resistance isn't constant. R is a variable. Light bulb V to I ratio is not linear.

4) Given #1, Y capacity is consumed at lower voltage and thus lower current, e.g., 1000mAh of capacity consumed at > 120V is at higher current and thus takes less time than capacity consumed at < 120V.

As an exaggerated example, using a HA automatic discharger that steps down the current at various levels (like swapping light bulbs), a severely voltage depressed pack may take 12 hours to discharge to 0.8V/cell. Subsequent discharges take 4-6 hours since the bulk of the capacity is extracted at higher voltage/current. All cycles extract similar capacities.

I don't know what the Genesis One logs, but time to 120V would be a very useful measure. If D1 to 120V takes 3 hours and D2 to 120V takes 3.6 hours, that's direct evidence of improvement. When you lump >1.0V capacity and <1.0V capacity as a single discharge time, the evidence for improvement is less conclusive.

As I indicated, nothing jumped out as negative. The data indicate that the pack did not experience a substantial improvement in capacity (about 16%), which is low for a pack with a lot of VD.

Maybe it will help for me to add that the battery may not be in a state where it will benefit from reconditioning, which may be good or bad. :)
 

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Discussion Starter #6
I don't know what the Genesis One logs, but time to 120V would be a very useful measure. If D1 to 120V takes 3 hours and D2 to 120V takes 3.6 hours, that's direct evidence of improvement.
Well, I do have time to 100V. From 175.6V it took 3.5 hours the first time and from 177.8V the second time it took 4 hours.
 

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Discussion Starter #8
Read it, maybe didn't understand it correctly. Assumed time to discharge to 100V would be almost as meaningful as to 120V with the other parameters being equal. Anyway, if nothing negative stands out, that's all that counts. Thanks for the analysis.
 

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Key takeaway is that the capacity below 120V isn't usable, and the amount extracted between 120 and 100V will vary depending on the amount of VD present.

Given that you're cycling to something around 0.8V/cell, you're probably not capturing a lot of the voltage depressed capacity, but you're minimizing potential for reversals, and 4.4-5.1Ah of capacity above 100V likely indicates a pack in a reasonable state of health.
 

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Read it, maybe didn't understand it correctly. Assumed time to discharge to 100V would be almost as meaningful as to 120V with the other parameters being equal. Anyway, if nothing negative stands out, that's all that counts. Thanks for the analysis.
These sound like good assumptions to me. :D

I think another 2-3 cycles down to 120V won't hurt as 5 cycles is apparently something used for conditioning (first link below).

Also, it would probably be best to allow the battery to rest after discharge until the voltage stabilizes before charging. Probably should wait the same amount of time after charging for a similar internal process to occur. It probably has a beneficial balancing effect. Reducing the charge/discharge current when you get near the end will probably have a similar beneficial effect. And cooling!

http://data.energizer.com/pdfs/nickelmetalhydride_appman.pdf
http://www.scarpaz.com/Attic/Documents/NiMH_technical.pdf
 

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@atikovi the more I think about it, the more I appreciate your starting this "shallow discharging results" thread.:D

I hope you do this three more times and also post the voltage at which you stop your recharge. :cool: I want to see how the capacity builds over several cycles!!!

For me, it spawned research on battery charging which, this time, came up with the two great links that helped me come to my own understanding of how these batteries work (past the mysterious "balancing" and "deep discharge" and the other generalities we use.)

I'm getting ready to finally build my grid charger/discharger and I think I'm going to grab me one of those 53 amp Meanwell devices and rig it up to run my car while I'm driving so that I can do several (relatively) uninterrupted cycles of discharge/recover/recharge/recover while closely monitoring with a 16 bit AD, and Arduino-controlled charging/discharging to slow or stop dis/charge at signs of reaching full charge or reversal of any one cell. I plan to try detect the first cell reaching max charge and reduce current to protect that cell; similar with discharging. Then let the battery "recover" which I hope is some kind of additional internal electrolyte/battery-chemistry balancing.

The idea: drive the car during the battery "recovery" cycles, using the 12V battery to start the car and the "no IMA battery" tricks plus Meanwell to keep the 12V battery charged while the IMA battery is disconnected and going through a "recovery" cycle.

Thanks, man!!! :cheers:
 

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These sound like good assumptions to me. :D

(1) I think another 2-3 cycles down to 120V won't hurt as 5 cycles is apparently something used for conditioning (first link below).

(2) Also, it would probably be best to allow the battery to rest after discharge until the voltage stabilizes before charging. Probably should wait the same amount of time after charging for a similar internal process to occur. It probably has a beneficial balancing effect. Reducing the charge/discharge current when you get near the end will probably have a similar beneficial effect. And cooling!

(3):
http://data.energizer.com/pdfs/nickelmetalhydride_appman.pdf
http://www.scarpaz.com/Attic/Documents/NiMH_technical.pdf
(1) Not worth the time. Key to recovering lost capacity is discharge BELOW 1.0V/cell.
(2) Not at all. There is absolutely no benefit to this "rest" whatsoever. Versions of the Genesis do taper current to 350mA at the end of the charge.
(3) These are basic primers and are worthwhile for CONSUMER grade cells. Their application is lacking when you start talking about cells that retain decent charge and can deliver 100A of current.

You really need to go to 99mpg.com and read everything about charging and discharging. Lotsa great graphs, stick and pack level work.

@atikovi the more I think about it, the more I appreciate your starting this "shallow discharging results" thread.:D

(1) I hope you do this three more times and also post the voltage at which you stop your recharge. :cool: I want to see how the capacity builds over several cycles!!!

For me, it spawned research on battery charging which, this time, came up with the two great links that helped me come to my own understanding of how these batteries work (past the mysterious "balancing" and "deep discharge" and the other generalities we use.)

I'm getting ready to finally build my grid charger/discharger and I think I'm going to grab me one of those 53 amp Meanwell devices and rig it up to run my car while I'm driving so that I can do several (relatively) uninterrupted cycles of discharge/recover/recharge/recover while closely monitoring with a 16 bit AD, and Arduino-controlled charging/discharging to slow or stop dis/charge at signs of (2) reaching full charge or reversal of any one cell. (3) I plan to try detect the first cell reaching max charge and reduce current to protect that cell; similar with discharging. Then let the battery "recover" which I hope (4) is some kind of additional internal electrolyte/battery-chemistry balancing.

The idea: drive the car during the battery "recovery" cycles, using the 12V battery to start the car and the "no IMA battery" tricks plus Meanwell to keep the 12V battery charged while the IMA battery is disconnected and going through a "recovery" cycle.

Thanks, man!!! :cheers:
(1) Again, discharges to 1V/cell don't accomplish a lot unless you do it 8-12 times for packs with severe VD.

(2) Reversal will be hard to detect. Mike's site may provide some guidance if he posted his source code. That is an option on the Genesis One - terminate upon reversal detection. The idea that you can reduce current to a "protective" level is off UNLESS you're looking to drop the discharge current to something around 50mA, which is not realistic. If you read the Energizer paper, you know that reversals at low current are not harmful for amounts < 50% of capacity, e.g., A cell that will deliver 5000mAh will not sustain damage until it has delivered that 5000mAh AND had another 2500mAh pushed through it. Cell reversals are routine and common. For short durations and low currents on cells like these, they are a non-issue. I have personally reversed on the order of 25,000 cells at least once. If it's for short durations at low current, there is never an issue. If it is for longer durations that exceed numbers similar to the 50% value given by Energizer, the cell is severely damaged, low current or not.

(3) Detecting -dV signals on the order of .005V with a pack at 170V+ is pretty much impossible. Temperature is a better indicator as is the <0.1C charge approach. With cooling, NiMH can tolerate extended periods of over charging at 0.1C or less. With most grid chargers peaking at <350mA, it's never a concern.

(4) Nope. The act of charging itself is what restores the terminals to the proper phase following discharges that consume voltage depressed capacity.

You seem pretty resistant to the information I'm presenting. To give you perspective, I have reconditioned well over 200 NiMH packs. I am giving you data based on experience, not theory.
 

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(1) Not worth the time. Key to recovering lost capacity is discharge BELOW 1.0V/cell.
The curves in the Energizer paper do suggest 0.8V gets you another few percent of discharge.

Speaking at the single cell level (not the pack level) what's the target discharge voltage to recondition a single cell?

(2) Not at all. There is absolutely no benefit to this "rest" whatsoever. Versions of the Genesis do taper current to 350mA at the end of the charge.
What's going on in the battery electrochemistry or mechanically that causes the recovery?

(3) These are basic primers and are worthwhile for CONSUMER grade cells. Their application is lacking when you start talking about cells that retain decent charge and can deliver 100A of current.
What technical details are missing from these papers, and can you point to some quality technical papers that speak to those details at greater length?

You really need to go to 99mpg.com and read everything about charging and discharging. Lotsa great graphs, stick and pack level work.
I'm really tired of reading hundreds of posts from uninformed sources, or worse, misinformed, authoritative sounding sources. Do you have some specific, highly authoritiative links?

(1) Again, discharges to 1V/cell don't accomplish a lot unless you do it 8-12 times for packs with severe VD.
Sure, I can see that, because the one or two or 5 dead cells are going to get lost in the pack.

(2) Reversal will be hard to detect. Mike's site may provide some guidance if he posted his source code. That is an option on the Genesis One - terminate upon reversal detection. The idea that you can reduce current to a "protective" level is off UNLESS you're looking to drop the discharge current to something around 50mA, which is not realistic. If you read the Energizer paper, you know that reversals at low current are not harmful for amounts < 50% of capacity, e.g., A cell that will deliver 5000mAh will not sustain damage until it has delivered that 5000mAh AND had another 2500mAh pushed through it. Cell reversals are routine and common. For short durations and low currents on cells like these, they are a non-issue. I have personally reversed on the order of 25,000 cells at least once. If it's for short durations at low current, there is never an issue. If it is for longer durations that exceed numbers similar to the 50% value given by Energizer, the cell is severely damaged, low current or not.

(3) Detecting -dV signals on the order of .005V with a pack at 170V+ is pretty much impossible. Temperature is a better indicator as is the <0.1C charge approach. With cooling, NiMH can tolerate extended periods of over charging at 0.1C or less. With most grid chargers peaking at <350mA, it's never a concern.
I'm OK with 50 ma. That's maybe 0.01C and will take a WHILE, but it's at the end of a higher rate charge.

Reversal detection sounds quite doable with a 16 bit A/D, proper EMI control, and monitoring each stick. I've been collecting harnesses for this kind of thing.

(4) Nope. The act of charging itself is what restores the terminals to the proper phase following discharges that consume voltage depressed capacity.
phase? it's dc

You seem pretty resistant to the information I'm presenting. To give you perspective, I have reconditioned well over 200 NiMH packs. I am giving you data based on experience, not theory.
I can understand why you might think I'm blowing off your advice, and I apologize. Let me explain. I have read enough posts of people losing batteries. This forum format is great for community but does not support the kind of curation needed to separate the wheat from the chaff. (A format like StackOverflow, which surfaces the best content, would be GREAT for this kind of Q/A!) I have seen this pattern regarding advice for other things on both this and other forums. Some of this advice has come from "authoritative" sources who turned out to be wrong. I was reminded of this just today in a different thread. I have also taken said advice and been bit on the butt by it more times than I want to admit.

So call me overly cautious and naive. Sigh... That's OK. I would prefer that and end up being informed and will hopefully admit my own mistakes along the way so that I can be freer to share them so that others might avoid them. I'm still pretty far from that, but it's a goal.

As for batteries, I want to know *why*. It's part of my DNA. If I don't understand why, I will keep asking. And, as far as experimenting, I have the skills to use microcontrollers to do a lot of my dirty work (monitoring and changing the charging profile based on what the battery is doing and generating data to baseline the cell for reference later). And I don't need it to happen tomorrow, because the Insight will run without the IMA battery. So I can wait for a process to finish.
 

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Many of your questions can be answered by searching the site for "Huggins."

For single cell, 0V target as there is a potential to gain additional voltage depressed capacity below 0.2V, and there is 0 concern with reversal.

"phase" refers to the constituents at the terminals.

50mA referred to the discharge current. There is no need to throttle charge below 0.1C, NiMH can handle it quite well. Since most use 350mA for charging, at least towards the end, no need at all. Read up on the operation of the Genesis One charger. And read Mike's 99mpg.com.

If you haven't encountered it, look for eq1's thread concerning using paper clips to short every other voltage tap. This activates the thermistors in the circuit, and they pull something around 50mA. It has the benefit of a very slow discharge with only 12 cells in a string, so the chances and severity of reversals are substantially reduced. The down side is it takes a very long time. IIRC, it's about a week to drain all 10 taps. He swears by the transformative nature of this process.
 

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Discussion Starter #15
(1) Not worth the time. Key to recovering lost capacity is discharge BELOW 1.0V/cell.
Isn't discharging to 100V just that? 120 cells/100V = .83V. Mike originally set the G1 to discharge down to only 135V. In the years after that he did further tests and determined deep discharging down to even 50V seemed safe. I got Mikes revised chip for the G1 which can automatically discharge to 100V, 75V and 50V over 3 cycles. The only reason I didn't do that this time is reading some of your posts saying the deep discharging may kill marginal packs. Would a third cycle down to 75V be beneficial or should I leave well enough alone if the data from the first two seem satisfactory?
 

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Isn't discharging to 100V just that? 120 cells/100V = .83V. Mike originally set the G1 to discharge down to only 135V. In the years after that he did further tests and determined deep discharging down to even 50V seemed safe. I got Mikes revised chip for the G1 which can automatically discharge to 100V, 75V and 50V over 3 cycles. The only reason I didn't do that this time is reading some of your posts saying the deep discharging may kill marginal packs. Would a third cycle down to 75V be beneficial or should I leave well enough alone if the data from the first two seem satisfactory?
Yes. He was recommending multiple cycles to 120V, not 100.

Given the estimated capacity, the battery doesn't look too bad. There might be more hiding out down below 100V, but it's up to you.
 

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As for batteries, I want to know *why*. It's part of my DNA. If I don't understand why, I will keep asking....
Here's a link to a post with a pdf attachment that includes what I've found to be the most powerful, comprehensive explanations for what goes wrong at the electro-chemical level and why deep discharge (really 'ultra' deep discharge) fixes stuff: https://www.insightcentral.net/forums/honda-insight-forum-1st-gen-discussion/81778-tinkering-non-working-ima-battery-8.html#post1206666

I originally posted the "Huggins" material Steve mentions - something I came across in a nice, big book way back when. That was the best explanation I found to that date of what Huggins calls "memory effect," which in his usage is synonymous with "voltage depression." But it really is a more narrow topic than what's needed to explain what goes wrong with Insight cells. Not to mention that the core of it is theoretical, not experimental... Huggins wasn't/isn't an expert on NiMH, either - I exchanged an email with him and that's what he said. He referred me to a couple others, with whom I exchanged a couple emails, too...

The pdf explanations are simply better - not as wonky and detailed, yet still detailed enough, and more comprehensive...
 

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For your convenience, I've posted below the content of the single post where sser2, the chemistry guy who started the thread I linked to, lays out his explanations for what goes wrong.* Note that I'm not just blindly adhering to what sser2 says, either. Most of what he describes is repeated in many other peer reviewed journal articles and books - and stuff - here and there, stuff I've read. It's just never been in such a user friendly, Insight specific context...

*https://www.insightcentral.net/forums/honda-insight-forum-1st-gen-discussion/81778-tinkering-non-working-ima-battery-6.html#post912394

12-23-2015, 07:27 AM #208, sser2
Although I didn't want to theorize, I cannot help doing it because the chemistry behind the deep discharge seems pretty straightforward. To my excuse, I was a chemistry geek at high school, and took extensive courses of inorganic and physical chemistry as part of my undergrad studies. I am a PhD in biochemistry, and chemistry is a significant part of my professional activities. So, in lay terms:

The negative (MH) electrode is of little concern from the point of view of cell's deteriorating capacity: it is purposely designed to have larger capacity than the positive (nickel) electrode. However, upon reversal down to -1.25 V, atomic oxygen will corrode it, causing reduction of its capacity. Atomic oxygen is a very potent oxidizer. Nothing can stand to it but noble metals like platinum.

Since the positive electrode is limiting to cell's capacity, its degradation is the key to the capacity loss. There are three major modes of degradation:

1. Large crystals of Ni (hydr)oxides with Ni oxidation states above 2. These large crystals form because the battery is never fully discharged in the car. Due to their low surface-to-volume ratio, they cannot support higher discharge currents, but can still support low discharge currents. At low discharge currents, these large crystals will be eventually converted into Ni(OH)2, and this way the larger crystals will be broken up into smaller entities, which, during the subsequent cycles, will be able to support higher currents. Another name for this phenomenon is memory effect.

2. Formation of γ-NiOOH. The normal isoform of the NiOOH in the cell is β, which is readily converted into the Ni(OH)2 during discharge. γ-NiOOH, which slowly accumulates as battery ages, is converted to Ni(OH)2 with more difficulty, and only after all the β isoform is gone. γ-NiOOH accumulates because the battery is never fully discharged in the car.

γ-NiOOH is bad in two more ways. It crystallizes with considerable amount of water, which sequesters water from the electrolyte, making the electrolyte less conductive. The consequence is increased internal resistance. When γ-NiOOH is eliminated following deep discharge, this sequestered water returns back to the electrolyte, and internal resistance decreases.

Sequestration of water in γ-NiOOH dramatically increases its volume. Whereas the β-NiOOH<=>Ni(OH)2 transition is associated with only 1-2% volumetric change, the γ-NiOOH<=>Ni(OH)2 transition alters the volume by whopping 40%. It is therefore much more destructive to the active layer of the electrode.

3. The active Ni (hydr)oxide layer of the positive electrode may lose contact with Ni foil support, or flake off, which takes it out of commission. The charge-discharge reactions on the positive electrode involve small, yet consistent volumetric expansion and contraction of the (hydr)oxide layer. This eventually causes material cracking and flaking, which in turn reduces the capacity of the electrode. γ-NiOOH exacerbates flaking of the active layer.

Ultra deep discharge remedies conditions 1 and 2 by eliminating the large crystals and γ-NiOOH. Interestingly, ultra deep discharge may also remedy the condition 3. As the cell gets below 0.25V, the nickel metal support of the positive electrode forms a galvanic pair with the negative electrode, and conversion of nickel into Ni(OH)2 begins:

Ni - 2e- = Ni2+
Ni2+ + 2OH- = Ni(OH)2

As Ni2+ ions are formed, they immediately react with OH- ions (from KOH) to form the insoluble Ni(OH)2, which is deposited at the electrode. Thus, the lost active layer of the positive electrode is replenished.
 
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