I agree with you about deep discharge. I bring the pack down to about 5 or 10v, and then a full grid charge. I only need to do this about once every 2 years to keep the pack running normally. Don't have any detailed metrics as you mentioned.

 

What discharge rate/load do you use?

The reason I ask is because it took me a long time of experimentation to see, to somewhat understand, that there's worthwhile gains doing very low current, very prolonged, very deep - "ultra"-deep - discharge. For example, looking at some graphs yesterday, I saw that my old, merely 'super deep' methodology considered something like 200mA down to 0.2V cell-level as sufficient. I was doing cells with a hobby-type discharger that would start discharging at say 1A down to 0.2V, but would then reduce current, holding 0.2V constant, until current reached 200mA. But later I shifted to 'ultra deep' - basically something like a 33Ω resistor at cell-level for as long as it'd take to not have voltage rebounding above about 0.9V max over a 12 hour period after the resistor was removed. 19.5 amp discharge graphs after each of these types of treatments show that the latter treatment produced much better results...

Which brings me to my main point. The main type of "gain" from this ultra deep discharge is obvious (in graphs) only if you're looking at a high rate discharge and the voltage. Capacity alone tells you little to nothing. In other words, looking at, for example, the graphs I mention above, the cells/sticks put out the same capacity both times, after each treatment. BUT, the curve of the second graph, after the ultra deep, is much loftier over the second half of the discharge [edit: actually it's loftier over the whole curve, but especially the second half. Compare first inflection point, after discharge begins, we see about 2.4V for the 'super deep' treatment vs. about 2.45V for the 'ultra-deep']. The cells also track better.

In a nut shell, the ultra-deep discharge can improve the power output of the cells (in addition to capacity - if they're capacity-stunted as well)... I think this is important when it comes to how the pack performs in the car, but it's often/always overlooked: If your cells can't maintain voltage under around the 50% charge state, your pack is quickly going to trigger recals. Etc., etc...

I guess I should post those graphs; this is just one example of what I've seen in other cases... These are 19.5 amp discharges on a stick, with voltage monitored on pairs of cells. Note how the roughly mid-point voltages for the lower pane are about 2.40V to 2.42V, whereas they're only about 2.33V to 2.36V for the top pane...

 

This is what's problematic with stuff you see/read at IC: no one looks closely enough at their pack performance to really know how they're actually performing. Most people are like, 'it doesn't neg recal' or 'there's no IMA light' - 'my pack is working great!' No, a great working pack has to hit certain metrics, certain benchmarks, in order to qualify as working great...

IMO the data is not readily accessible. I've tried to get more info.. My ECU scanner can access this information but at only a few messages per second, it's not really possible to get great data. Does one of the member diagnostic tools log enough data to do data logging of enough metrics (current demanded, current supplied, etc etc) to create a bunch of data that can be mined for trends? Or are we looking at reading data lines to get commands sent from the ECU to BCM, and reading voltages and currents to see the result of those commands?

Also, has anyone with any significant mileage been able to keep their original battery alive with grid charging and/or discharging, or are most folks on replacement batteries?

 

Does one of the member diagnostic tools log enough data to do data logging of enough metrics (current demanded, current supplied, etc etc) to create a bunch of data that can be mined for trends? Or are we looking at reading data lines to get commands sent from the ECU to BCM, and reading voltages and currents to see the result of those commands?

Not sure I understand the second part of your response. But yeah, the OBDII&C is the tool to use to get this kind of info/data. You can log 8 parameters of your choice, such as amps, volts, state of charge, pack temp, whatever, yet I don't think you really need to log to read the health of your pack. You just need to take some quick peeks at the digital readout of amps and volts when you're subjecting the pack to, say, 20 amps of assist... Hit a slight incline, have it in 4th gear, press the throttle moderately, enough to invoke assist, and hold it there - it usually pans-out to about 20 amp assist that's easy to hold. What does the voltage readout say? You'd also be reading pack temp - cooler temps you'll get lower voltages, so you factor that into the interpretation, for instance. You'd look at state of charge (Soc) - as I mentioned, you really want to be able to be under 50% yet still get the full assist values - the more assist, the lower the SoC the better. Etc etc...

But, I don't think the OBDIIC&C is absolutely necessary to get a much better read on pack health. I think just looking at total pack voltage with a multimeter while you're driving would work. Maybe bring the BAT (charge state) bars down, well, at least off the top few bars, hit a slight incline in 4th, invoke assist at modest throttle, and it's almost always around 20 amps or so - 18 amps, 27 amps - whatever, somewhere around there. Look at your voltmeter readout and it should be holding fairly steady above about 140V. Ideally it'd be higher, but 140V is probably a good ballpark, cutoff-type value. Even just noting the change is good - voltage shouldn't drop precipitously; it should be holding fairly steady with only a little bit of gradual decline, as you hold assist as constant as you can...

To get even less technical but not so less useful, you can simply watch voltage a bit when you're holding whatever assist level as steady as you can: voltage should hold fairly steady. If voltage drops like 1 volt, 1 volt, 2 volts and lower still, that's a sure sign your pack needs attention. Good packs hold voltage fairly steady, just a little drop, gradually, and even down to quite low charge state levels... Bad packs - voltage drops obviously, never seems to stabilize. You'll hit say 147V at first few seconds of modest assist, but shortly thereafter it's just drop, drop, drop...

And the thing is, this can all happen - "this" being the drop, drop, drop, etc. - and there really isn't anything the car, the BCM, the gauges, the trouble lights - will do to tell you your pack is in bad shape. That is, until it's really bad...

Also, has anyone with any significant mileage been able to keep their original battery alive with grid charging and/or discharging, or are most folks on replacement batteries?

I don't know. I have an original battery that 'threw codes' at one point, that's when I picked it up from someone. I've done my things to it and it has, for the most part, been kind of blowing my mind. I've been at this for quite a long time now, and until this particular pack and 'these treatments' I've simply been unaware of the high performance capability of used Insight packs. I mean, I was kind of just throwing this pack together - I had been using a couple of the sticks as a 12V battery for months, for instance, and was thinking I'd be using some sticks from another pack. But then I just decided to keep it all original, despite having what seemed to be a few weak sticks plus the dubious reuse of those 12V sticks along with the others that had no such different usage. Etc. Well, after some treatment, monitoring, etc., this original pack is doing full-blown full assist at like 40% state of charge, for instance, at not very high temps (you can only get true full assist above something like 77F, so I've seen say 90 amps at 77F+, and some lower amount at lower temps, but still high values)... So, I don't know, considering that the pack was failing when i got it, just like so many other people's packs have failed and are failing, I don't see why other people's failing packs can't be reconditioned to perform like mine is... I guess that's partly why I'm bothering to write anything here at all, it makes me kind of sad to see so many people complain about their packs when I'm like going full throttle with a 60 degree F pack at 40% SoC and the pack's not batting an eye...

 

Personally, I'm a proponent of 'ultra deep discharge' - very low current, prolonged, as disaggregated as possible (i.e. less than whole pack) discharging, followed by a grid charge. With this strategy I don't think it matters whether you grid charge first or not, as the load used is so small and you're preferably only dealing with at most 12 cells in series rather than 120, that cell reversal isn't an issue... Here's a link to some theory underlying this 'ultra-deep discharging' process: https://www.insightcentral.net/foru...m-1st-gen-discussion/81778-tinkering-non-working-ima-battery-8.html#post1206666

I agree with you about deep discharge. I bring the pack down to about 5 or 10v, and then a full grid charge. I only need to do this about once every 2 years to keep the pack running normally. Don't have any detailed metrics as you mentioned.

You agree with him, but you do it anyway? Likely that a single low current discharge to 96V (.8V/cell) will get you just as much good with far less risk.

IMO the data is not readily accessible. I've tried to get more info.. My ECU scanner can access this information but at only a few messages per second, it's not really possible to get great data. Does one of the member diagnostic tools log enough data to do data logging of enough metrics (current demanded, current supplied, etc etc) to create a bunch of data that can be mined for trends? Or are we looking at reading data lines to get commands sent from the ECU to BCM, and reading voltages and currents to see the result of those commands?

Also, has anyone with any significant mileage been able to keep their original battery alive with grid charging and/or discharging, or are most folks on replacement batteries?

Peter's OBDIIC&C permits logging to excel. SoC, pack voltage, current in and out, net Ah, etc.

 

The moron at the back of the class

I have waded through all the threads I have found so far. It’s a bit like reading a foreign language I barely speak. But I’m learning a lot, about large and small Chrystal’s and their relative surface areas available for the electro chemical reactions that make electrons flow and their relationship to battery function, memory, flaking off at the positive electrode etc. etc. etc. you guys are doing the
Deep digging to figure out finally how to effectively keep these batteries alive. And you have been doing it for years the earliest threads start, what five, four years back. You use diagnostic tools I would need training to learn how to use.
I don’t think I am unusual in that I will not go to that extent to maintain my battery or modify my car. But I can read directions and plans. Your threads tell me you right now have it mostly figured out and if I may:
It’s this: the way the car manages the battery doesn’t exercise the battery through its full range of levels of charge from high to low. This results in the electrolytes chrystalysing in ways that limit the batterie’s range of effective operation to a narrow range of charge, say just for example from 50% to 80%
Resulting in only 30-40% of its potential power out put. But the car continues to operate like it expects 70-80% output. This stresses what’s left of the battery and in the end wears it out prematurely. Again I’m a moron when it comes to this. But I don’t think I’m alone. The take away tho, is that at this point you have come to the conclusion that a slow very deep discharge and then a complete charge afterward, done from time to time erases these chemical “memory” effects” to a great degree. Allowing the battery to last a much longer time and perform much better. What I think I see though I don’t begin to see it
In the detail some of you do. Is that you recently brought it into sharper focus than at any time before. What I think, is it might be time to creat a new up dated recipe for battery maintainance for the rest of us. An idiots guide as it were. Something simple, maybe not perfect but attainable and adequate.

 

a-hem, I think we're a long ways off from ever figuring out much. I don't think any of 'us' do much deep digging any longer, I know I don't - plus, there's only so deep you can go until you bump into having to know a whole field of study, chemistry, and within that some nuances, weird stuff, that no one has ever spent much time working to figure out... And then this doesn't even include all the stuff you need to know, all the stuff you'd need to do, to figure out what the car electronics and computers are really doing. Etc etc... But, having said that, I do think the ideas at the thread I linked to earlier go the farthest in explaining most of the deterioration phenomena our cells/packs see - and these explanations are based on what I gather are fairly straight forward, common concepts among chemistry people.

The point here is that you probably shouldn't take whatever I write too seriously...

Your threads tell me you right now have it mostly figured out and if I may, it’s this: the way the car manages the battery doesn’t exercise the battery through its full range of levels of charge from high to low. This results in the electrolytes chrystalysing in ways that limit the batterie’s range of effective operation to a narrow range of charge, say just for example from 50% to 80%, resulting in only 30-40% of its potential power output....

I don't really know what's going on, but I have some semi-educated hunches. The car doesn't use the full range, but I don't think that's the problem, exactly. If anything, it's that the car uses a very narrow range - nothing even close to full - and that range of use is concentrated sort of toward the top, call it 65% to 80%. It might be higher, like 75% to 90% actual, but nominally it's around 65 to 75 or 80. I don't know exactly what the link is between this kind of usage and the deterioration we experience, but it's probably more or less due to what I quote below, regarding 'large crystals'.

In general though, it just seems to me, based on the tidbits of stuff about NiMH that I've read and what I've seen experimenting with charging and discharging sticks, packs and cells, that this chemistry screams for more balanced usage. To my eye, the cells need to be used in the middle of the charge state range most of the time, and occasionally stretched out to the ends - to top and bottom. It does seem to me that, once you can start using a lower and lower charge state range, the more you use it the better. But that could simply be an artifact, a repercussion, of having the cells used in the upper charge state range their whole life. It could be that, if the cells had been used in the middle from the get-go, they wouldn't benefit from concentrated use at the bottom...

Anyway, it's not the electrolyte that crystalizes. sser2 in that linked thread mentions that, among the three or so causes of deterioration he suggests, larger crystal formation is one of them. Here's exactly what he writes about it:

"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."

So, the car concentrates usage in the upper charge state range, whatever parts of the cells correspond to that range get used more, while other parts get used less. Larger and larger crystals form in these unused portions, they support lower and lower currents, which means power output decreases in those lower charge states. This also means that capacity (amp-hour capacity) effectively shrinks - because the car's lower cutoff is in part based on voltage and voltage is now sagging more and more, earlier and earlier, in that lower range. So the car starts charging the pack earlier, more often, and usage gets even more concentrated in the upper charge state range. And the cycle keeps repeating...

I'm not sure this is the big kahuna of failure modes, but it's a big one. Somewhere in the process I think uneven cell usage has to come into play, where some cells perhaps get hotter and wear differently - because imbalance seems to be the more common problem... I think I'd say this is the most glaring problem with the car's management and probably spawns all the other problems that rear their heads along the way to neg recals and IMA lights...

....it might be time to create a new updated recipe for battery maintainance for the rest of us. An idiots guide as it were. Something simple, maybe not perfect but attainable and adequate.

I might add some material that explains my 'tap-UDD' process, ultra-deep discharge at the voltage tap level. I've thrown some of it out here and there already. I think it's probably the easiest, safest (from a cell-damage perspective), most effective way to recondition. Not much labor input, simple to do, should/seems to achieve what needs to be achieved. It does take a relatively long time though, like a couple weeks of one driving in IMA bypass mode...

 

Well Mike invested considerable effort in trying to understand NiMH batteries.... You have said that you don't always understand what is happening. Most folks who have tried to understand the "art," if it can be called such, have walked off shaking their heads - plus, OPINIONS have changed over time. No need to throw away everything that has been written.

Yeah, I don't think I'd argue with what you say here. I guess I'm trying to some degree to focus on the few things I mention in the first post rather than rehashing all the trivia, all the circumstances, etc., loosely related to 'Insight packs' and 'NiMH'... Let me see if I can summarize - really pull-out the crux of the matter...

The three things I mention in the first post:

1) limits of grid charging-only,
2) how a healthy pack should actually perform, and
3) the function of deep discharging.

In my view these things tend to get lost (or have never actually gelled) in the advice usually provided and the discussion that may follow when people come to IC asking 'What should I do with my IMA?'.

I've been at this for 6 years now, early-on quite concerted efforts to figure out what's going on, and then later just kind of hodge-podge following through as best I can with whatever aspect regarding reconditioning pops up in my life. Based on the last couple years or so of experimentation with ultra deep discharge and the results, I'm becoming more confident in the idea that ultra-deep discharge can make a significant - and perhaps crucial - difference in the outcome of reconditioning efforts. I want to say that the extent to which grid charge-discharge types of reconditioning fail or don't last probably has at least a lot to do with the extent to which the grid charge-discharge process has been carried out to its fullest. Pack management and pack performance in the car hinge seemingly delicately on the balance of cells - they need to perform as closely as possible. To me it looks like one of the only ways to achieve maximum balance is to do ultra-deep discharges. Deep, super deep, sort of deep - they inevitably end up treating cells differently, cells still end up being too different, and the pack will fail sooner rather than later...

A lot of my early efforts with whole pack deep discharge didn't quite meet the mark, and then, when more people started to try whole pack deep discharge, we saw that some people's packs ended up failing (likely too-deep reversals at too high a current for too long). Then the kind of standard approach became suggestions like 'just grid charge, that should be enough,' or the 3 cycle grid charge-discharge approach with not-so-deep end voltages... I don't think I'd argue that these don't help or can't help or aren't the right thing to do in some cases. I'm questioning whether these approaches are really just a part of what seems like the real-deal process and perhaps whether it'd be better to do something else most of the time, like a tap-level ultra deep discharge...

Part of the problem is that the bar is set too low in what constitutes a reconditioned pack, a healthy pack, a pack that now works yet didn't before. Take what Peterboat writes above as a case in point:

"Before Christmas I was having IMA light problems, I did a grid charge and then last week did another. The results has been the gauge is staying much higher, no recals, and the battery is defo performing better. I have plans to do a deep discharge, Peter [Perkins] says take it down to 100 volts then grid charge up, and then discharge it to 75 volts and grid charge it up again. So in the near future I will be doing just that, however for the moment the battery pack is doing just fine."

Here the metrics used to determine pack health are the gauge staying much higher, no recals, a butt-dyno sense that the battery is performing better. Peterboat thinks his pack is "doing just fine." But is it really? One thing I'm saying is that we should use better metrics to measure pack health - and that it's not that hard to do. I mentioned some criteria earlier.

I think this is really important, maybe even the most important. Because a pack can seem to work just fine very easily yet still be seriously under-performing. It took me a long time to see that, to figure it out, and that's me being into it and really looking for it... I don't think I'm concerned so much about performance for performance's sake, but rather, I'm concerned most about the effectiveness, the longevity, of the reconditioning process.

I kind of think that, if one's reconditioning process can't get the pack to put out about 80 amps at 40% charge state, then the reconditioning process won't last long and/or simply wasn't good enough. My hunch is that few packs reconditioned according to the 'standard' approach can probably put out 80 amps at 40% charge state. My hunch is that few packs reconditioned according to the standard approach could even get state of charge down to 40% without having a neg recal... And it's not that this performance is so crucial or wonderful - it's that it means the pack will be performing better, longer in the normal day-to-day type operational circumstances. It will stay balanced better and longer. It will have less self-discharge. It will run cooler. Etc etc...

 

Before Christmas I was having IMA light problems, I did a grid charge over Christmas [IMA gauge only on one bar!] and then last week did another grid charge in a warm garage. The results has been the gauge is staying much higher, no recals, and the battery is defo performing better.
Now I have plans to do a deep discharge, Peter says take it down to 100 volts then grid charge up, and then discharge it to 75 volts and grid charge it up again. So in the near future I will be doing just that, however for the moment the battery pack is doing just fine...............fingers crossed

 

Not much to add.

But I have just left a pack deep discharging on my bench while i'm away for ten days..

Basically I cycled it as per my original thoughts, and now when it is discharged to around 144v nominal I have attached a fixed 3.2k 10w resistor too it to continue until empty at <50ma rate and decreasing quickly as the voltage dwindles.

The low current and long period i hope will minimise any damaging cell reversal.
It's almost like an exacerbated/faster self discharge..

I'll report on the on/off load pack voltage when I get back.

 

I have just left a pack deep discharging on my bench while i'm away for ten days. Basically I cycled it as per my original thoughts, and now when it is discharged to around 144v nominal I have attached a fixed 3.2k 10w resistor to it to continue until empty at <50ma rate and decreasing quickly as the voltage dwindles....

I'll report on the on/off load pack voltage when I get back.

Any updates on this? What was the final discharge voltage after your ~10 day discharge? Did you happen to check the rebound voltage, after removing the load - like what was the voltage when you put the grid charger on and how long had it sat between load removal and grid charge?

 

That sounds about right... When I was working with cells, I found that about a 20mA rate at about 0.7V was enough to 'cut through the fat' in a reasonable time, but not too much to blow right through it. At 3.2k, you'd be looking at about a 26mA rate at 84V... As far as I can tell, once voltage gets really low (discharging a string), voltage on 'stubborn' cells will rise, such as out of slight reversal, and those cells 'burn' again, until they all even out. Cells sort of oscillate up and down in voltage until they peter-out in the low double-digit mV level...

 

In my case I am lucky to have Peter Perkins on the doorstep to help, also my pack has only done 51k [december 2005 car imported from Japan] so it seems to have responded to grid charging.
I will be following Peters instructions using a low wattage bulb to see if that helps, however over the last couple of days I have done 700 miles and the IMA light has remained off.
I will plug my diagnostics into it today and interrogate it to see if the IMA fault is still present.
I have to say that this forum is the reason I bought this car as it provides the help to run what is a very rare car with specific needs that move it out of mainstream motoring.
On another point we are thinking of buying a CZR however I am thinking of either an 2010 one or going later for a 2013 model year with the lithium battery pack, what do the experts think?

 

In my case I am lucky to have Peter Perkins on the doorstep to help, also my pack has only done 51k so it seems to have responded to grid charging....

You have an original pack with only 51k? If that's the case I wouldn't think it'd need much to be reconditioned into being a top performer... Do you have an OBDIIC&C? If so, you should do some testing - pull the state of charge down (preferably below 50%), hit it with full assist: What's the voltage? Is it fairly steady or does it drop rather fast?

 

Thinking I should post sser2's chemistry explanations of why ultra-deep discharge works directly in this thread. This was from the end of 2015, originally posted here: https://www.insightcentral.net/foru...um-1st-gen-discussion/81778-tinkering-non-working-ima-battery-6.html#post912394

Lightly edited, highlighted:

"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 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 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 crystalizes 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 a 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 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."

* * *

All of these explanations are pretty consistent with what I've read in other places. For example, Huggins discusses γ-NiOOH formation. Mike D. used to come across dried-out, patchy separators when he opened-up cells, which led him to believe that electrolyte loss was one of the main failure modes. That's consistent with what sser2 says about γ-NiOOH, electrolyte sequestration, major increases in volumetric expansion and contraction, and cracking and flaking. I've seen the 'cracking and flaking' idea suggested as one among few major failure modes in NiMH posed in research papers... etc etc...

Of course, at the 'street-level', a lot of the interest in 'deep discharge' stems from what stick putzers have seen after dealing with deeply self-discharged sticks: charge them up and they're usually miraculously healed. In the old days, I used to cycle sticks 3-5 times at about a 1C rate - that was the program (everybody was doin' it). The cycles didn't go lower than about 5.4V - the 0.9V per cell cutoff. You can do that all day yet never see the gains you get simply from charging a deeply self-discharged stick. Again, it's like there's a full process, from start to finish, of which these types of cycles are merely a part...

At some point maybe a year ago or so, I experimented with ultra-deep discharge on already deeply self-discharged cells and sticks. I found that even ultra-deep discharging cells that were already deeply self-discharged would produce worthwhile gains... Typically, self-discharged cells end up at a voltage above about 0.5V, I have usually seen right around 0.68V. Perhaps any gains going even lower have to do with what sser2 suggests in point 3 above, where going below 0.25V can end up converting Ni to Ni(OH)2...

 

Wikipedia article re: discharge of NiMH

i am sure that Insight folks are familiar with this article, but thought i should mention it to hopefully get some feedback on it. When i searched Ni-metal hydride battery today the Wikipedia article said that it is best not to discharge below 1.0-1.1v per cell and that going lower can cause reversal in multi-cell packs. This would only bring the pack down to 120V. i am finally cycling my pack and am just starting the third discharge(i may not go too low). Any thoughts on this would be great. Blessings to you all.

 

i am sure that Insight folks are familiar with this article, but thought i should mention it to hopefully get some feedback on it. When i searched Ni-metal hydride battery today the Wikipedia article said that it is best not to discharge below 1.0-1.1v per cell and that going lower can cause reversal in multi-cell packs. This would only bring the pack down to 120V. i am finally cycling my pack and am just starting the third discharge(i may not go too low). Any thoughts on this would be great. Blessings to you all.

Beaten to death. Reversals have been demonstrated to occur and they are not automatically a bad thing. Energizer states that you can reverse a cell for up to 50% of its capacity before damage occurs, e.g., if your cell has 6500mAh of capacity, you can reverse it for 3250mAh of additional extraction before damage occurs. Lower current is better.

Mike D reversed a cell at 2A to -1.8V several times and cycled tested it. It performed as well as others that hadn't been reversed (link in sig).

Worried? Discharge to 96V (0.8V/cell). Either it will help a pack that will benefit from it, or it may damage a pack that is already on its way out.

 

A direct link on the article would be helpful for evaluation.

 

Ni-metal hydride Wikipedia article

Thank you Willie, Hoping to send the link to this article, but i am not too computer literate. https://en.wikipedia.org/wiki/Nickel%E2%80%93metal_hydride_batteryhttp://

 

Ni-metal hydride Wikipedia article

i will have to try that again, the link did not come through properly. https://en.wikipedia.org/wiki/Nickel–metal_hydride_battery

 

Deep discharge adventure

Sorry, just got back to a computer to be able to respond. I did take the pack down to 60 volts, but did not check the rebound voltage. I seem to remember it was rebounding very quickly after removing the 25 watt bulb. The car got parked but was started to move it in the yard about three to four times times -still hanging at 19-20 bars. Today i noticed the 20 bars displayed before were down to 4 bars so i put the charger on it again(it was down to 161 volts). I am thinking that i may have to cycle the pack again and go for a deeper discharge this time...

 

Sorry, just got back to a computer to be able to respond. I did take the pack down to 60 volts, but did not check the rebound voltage. I seem to remember it was rebounding very quickly after removing the 25 watt bulb....

I was asking about Peter's 10 day 3.2kΩ discharge... You might want to try a tap-level ultra deep discharge, here's a link to a post with a brief description of the process: https://www.insightcentral.net/foru...ical-issues/89298-quintessential-insight-nimh-voltage-thread-2.html#post1421333

 

I’m getting ready for my if it ain’t broke IMA idiots guide to battery health fix.My car drives great. I have no codes. My battery never reads more than two or three bars down and quickly recovers. Battery never replaced. 150K mi. I have: a grid charger, a light bulb discharge set up. Two 150w, two75w., two 25w, bulbs. A voltmeter. An idiots understanding of electrical theory. I have read the haystack of threads on the subject. Sometime in the next two months I want to do the right thing for my car. Will it take a couple days. Or More. One, two or three charge discharge cycles? Does it need to be 100%, 95%, or 90% perfect.
grid charge to what? 172 volts. Discharge 150w for ? Hours. 75w for ? Hours.
25w for ? Hours, ? Volts? Then grid charge again. And so forth. How many times? I Just want a practical plan of action.

 

Grid charge for 10,400mAh input
Discharge to 144V w/2X 150W wattage bulbs IN SERIES
Discharge to 120V w/75W bulbs IN SERIES
Discharge to 96V w/25W bulbs IN SERIES
Grid charge for 10,400mAh input
Discharge to 144V w/2X 150W wattage bulbs IN SERIES
Discharge to 120V w/75W bulbs IN SERIES
Discharge to 60V w/25W bulbs IN SERIES
Grid charge for 10,400mAh input
Discharge to 144V w/2X 150W wattage bulbs IN SERIES
Discharge to 120V w/75W bulbs IN SERIES
Discharge to 60V w/25W bulbs IN SERIES
Grid charge for 10,400mAh input

If you can monitor the discharge current and record time, voltage, current periodically, you can calculate the capacity of your pack. If you do this, make sure you record 144V, 132V and 120V readings

 

What does grid charge for 10,400 mAh input mean? How do I measure for it??
What readings for 144v, 120v, 60v? Time to get there? Like I said, electrical idiot.
In series, I get.

 

10,400mAh

If your power supply is 350mA, you charge for 10,400/350 = 29.7 hr.
If 300mAh, 10,400/300 = 34.7 hr

 

S. Keith, thanks.

 

Just for a point of reference. Could you give me an estimate of times for discharge. At 40 degrees f.
From full charge.
150w bulbs to 140v. Time?
75w bulbs to 120 v. Time?
25w bulbs to 92v. Time?

And for the second and third discharge

25w bulbs to 60v. Time?

Again, hip shot estimates so I sort of know how to monitor things this first time around.

 

No. It varies from battery to battery, it's condition and how effective each discharge is in restoring capacity.

Each phase will change on each cycle.

Try to check it at least once per hour. If it's bed time, and it's over 120V, install the 25W and let it run overnight. Take what you get.

General:
Cycle 1:
high watt discharge goes pretty quick.
mid watt discharge takes awhile
low watt discharge takes a long time.
Cycle 2:
high watt discharge takes longer
mid watt discharge takes notably less time than the first time.
low watt discharge takes notably less time than the first time.
Overall will take less time than #1
Cycle 3:
Like cycle 2 but less pronounced a jump than what was experienced between cycles 1 and 2.
Overall will take a little less time than #2

It changes because you're "moving" the capacity you discharged at lower currents/voltages to higher currents/voltages.

 

Damn! Just when I thought I had a sweet simple plan: S Keiths. Then eq1 steps in.
So I re read the whole thread and side threads and links.
I have to say theres an elegance to eq1’s clip short method that is hard to ignore. That photo with the penny for scale. Paper clips, black tape. Too much!
Then the ceramic light sockets in series with different light bulbs. And S Keiths
Simplified chart. Also clean,
I sense that with all the discussion these two approaches — approach, the same,
What’s the word? Asymptote (sp?) IE get closer and closer without ever actually getting there. Which is enough.
So : paper clip : two plus weeks, very little oversight necessary.
I’d have to figure out how to disable IMA assist if I want to drive

Light bulb discharge, : less open battery pack time. More oversight. I’m guessing a week down time for the car. QUESTION? What if the car were driven a few miles between each of the discharge-charge cycles?
I know i’m Dithering here.

 

Asymptotic

The bottom line is that there has been no substantial progress in the practice since Mike D's pioneering efforts. HA's new automated discharger is pretty awesome, but it just does what lightbulbs do automatically... but it's still doing fundamentally the same thing.

One area that I will ALWAYS disagree with anyone on is proposing a discharge PRIOR to a balance charge. I don't care what the circumstances are, you always start with a topping grid charge. Always. Period.

If you opt to do eq1's process, I vigorously recommend a 10,400mAh input charge and the prescribed whole-pack discharges down to 120V. Then procede with the paper clips.

I personally don't think eq1's process does anything for you that traditional grid charge/discharge doesn't already get you... well... maybe the pack level stuff cleans off 95% of the "crud" and the brutally slow discharge gets another 4.99%, but that's not relevant from a practical purpose. While eq1 has presented "before" and "after" discharges, I can't see that he's done anything comparing the two results, i.e., a 19.5A discharge to 6V has a slightly lower voltage before the deep discharge vs. after, BUT has that been confirmed?

For example, had he just recharged and discharged the same stick instead of the deep discharge, would he have seen a comparable increase in discharge power via slightly higher voltage? Probably. I've personally seen it many many many times (thousands) following more "traditional" processing. His solution is novel and likely as effective as any "traditional" method, but I don't see any evidence that it does anything different or better, and it definitely won't resurrect a dead cell.

 

Do you guys disconnect the 12V battery while discharging or recharging? I have Peter´s built in charger and somehow my HV battery was not full after 48h of charging...

 

You don't disconnect the 12v battery.

 

I realise this is a VERY old thread, but I’ve found it really interesting to read, even if I don’t completely understand many of the theories.

So this is my first post after acquiring a 2001 CVT, which was originally a Japanese market vehicle (no rear wiper) that was imported into the UK many years ago.

I have wanted a Gen1 Insight for many years and viewed and test drove four other cars before purchasing this one. I went in, eyes wide open, expecting issues that I’m happy to address over time. Main requirements were that it must be original with no parts missing and be able to move under its own power so that it can be shuffled around in front of my house.

I’ve been dabbling and finally began looking into the condition of the IMA. As purchased the car came fitted with a grid charger, but no means of discharging. I’ve now got the IMA lid off and measured 169v after about an hours charging (prior to this the IMA light was on). Yesterday (19:00 hours) I connected a jury rigged discharging contraption using a 40w light bulb (all I had!) connected to the same pack connections that the grid charger is connected to. 15 hours have now elapsed, and I can see that the bulb is still glowing reasonably brightly. I am reluctant to disconnect the bulb to get a voltage reading, and my gut feeling is just leave it connected until
It’s no longer illuminated, and then take a finishing voltage and a bounce back voltage before plugging the grid charger back in.

So, my few questions at this stage are…

1. Am I doing the right thing?
2. Does anybody want to predict the outcome?

I’ve literally owned the car a week and am not an electronics expert, so please don’t burn me to the ground 🤣. Also, the car is not currently Road legal, so I am doing the grid charging as I work around other jobs like minor leaks (rear upper seam?) getting into the rear luggage area.

This is a great forum

Thanks
Bob

 

I realise this is a VERY old thread, but I’ve found it really interesting to read... I’ve been dabbling and finally began looking into the condition of the IMA. As purchased the car came fitted with a grid charger, but no means of discharging. I’ve now got the IMA lid off and measured 169v after about an hours charging (prior to this the IMA light was on)...

I’d assumed that the pack was at full charge prior to charging because it measured 169v DC.

I re-read most of what I've written here, I don't see anything too glaringly out of whack.

I'm not so bullish on "ultra-deep discharging" any longer, too many different bad pack scenarios to recommend a one-size fits all thing like that. Plus there's probably other possibilities as to why I've seen gains after ultra deep discharges in the past to say for certain that it helps. Et al. I think my recommendation now is simply very very low current discharges at cell-level down to about 0.5V, which is a time consuming thing to do, so in lieu of that it's do whatever you can to approximate this as closely as possible.

Another thing is I make no mention of self discharge. I think uneven self discharge is probably the most important and debilitating form of degradation. If a single cell gets faster self discharge - and it doesn't even have to be that much faster - it will cause dysfunction quickly, and it's not reversible. This is probably way more common than I've thought in the past. Not that I do much with sticks and cells these days (though I happen to be dallying with some sticks and cells over past few weeks), screening for fast self discharge cells is pretty much the most important and sort of only thing I look for now. The rest of any 'degradation' can be fixed or worked around...

troytempest, you should probably verify what kind of pack you have - Is it aftermarket or original? My understanding is that aftermarket packs, especially earlier ones, don't handle grid charge and particularly deep discharge well.

You mention that your pack was 169V after an hour of charging(?), and then later assumed it was full prior to charging because it was at 169V (resting voltage?)? Well, 169V on a grid charger is probably not full. You'd have to see a peak over 172V (probably around 174V-176V) at typical temps for it to suggest a full pack, though if a charger were to keep going for a while after that, it's possible voltage could fall as low as 169V and be full/overcharged...

169V resting? Probably not full, not chock-full for sure. That might be a typical voltage for a car-charged pack that's been charged to the top of its typical usable range. But not truly full. It could be way far from full, too, depending on the condition or whatever of your pack/cells... Basically, off the top of my head, truly full and decently conditioned cells should be able to reach a resting voltage of 1.44-1.45V (~174V pack). Anything lower suggests either not full or not very well conditioned. This would be at around 26 degrees C, adjust lower by ~0.3V (for pack) for each degree C above 26, and ~0.3V higher for each degree C below 26C, roughly... In practice measuring this kind of stuff is difficult, so really the best way to judge 'full' is to watch for peak voltage, plateau, and decline, and temp too if you have an infrared thermometer or maybe an OBDIIC&C.