Honda Insight Forum banner

1 - 9 of 9 Posts

·
Registered
Joined
·
6,157 Posts
Discussion Starter #1
It's been about a year and a half since I installed what I said would be the last Insight NiMH pack I'd work on/with, having gotten tired of it all. But, this original pack in its reconditioned state has been working awfully well and has been producing some surprising results. It works in ways that I never thought possible with Insight NiMH. That's mainly why I'm here, one particular aspect, that makes we wonder about the car's stock management and the way the pack - a good pack - should actually perform...

It's all kind of complicated so I'll try to stay as focused as possible on only the 'main thing'. That main thing is this: I can use the pack at what seems like an historically low state of charge, get full assist, and have voltage remain high and stable despite that low state of charge, cool temps, and relatively high assist discharge... This, plus what I've seemingly done to achieve this, plus what appears to be improvement over time/usage, makes me seriously question whether the stock pack management has a major flaw, a flaw that causes deterioration...

In a nut shell, I finagle pack management with the OBDIIC&C and calpod clutch switch, basically forcing usage of the pack in a relatively low charge state. This has allowed me to get a better read on what happens 'down there'. You gotta do this 'finagling' most of the time, otherwise, the car will background charge and such and keep the pack at a higher charge state.

The thing is, if you do this, the pack - my pack, at least - will fairly quickly... 'acclimate' at the lower charge state and it will start looking and performing just as it does at the higher charge state... I'm mainly talking about voltage. If you start at a high-ish charge state and discharge (use assist) for a long stretch, pack voltage will drop and stay pretty low, say around 152V instead of around 161V. The car will background charge. But, if you purposely try to use the pack in that low charge state, doing assist and regen around say 40% state of charge, the voltage will fairly quickly come back up - it will gravitate toward about 161V, not that lower 152V level that it started at...

Say you discharge from 70% to 45%. Pack starts at 164V at rest and ends at 152V at rest. The car tries to background charge but you hit your calpod switch instead, preventing it. You purposely use the pack at around 40% to 50% for a few up-down cycles. Soon, pack voltage will pop back up to around 161V - at that 45% charge state - not the 152V you started at...

Now this, I think, is the crux of the potential stock mismanagement. It appears that background charging at least sometimes responds to voltage, most likely tap voltage. The problem with this, it seems, is that there's too much 'hysteresis' in the voltage behavior... It seems pretty clear that if I force pack usage at progressively lower charge states, letting voltage 'acclimate'/adjust or whatever each time, background charging won't kick in as soon and/or as often as it otherwise would. It really looks like the car is using tap voltage at least in part to decide when to background charge: on the first cycle down, say to 45%, voltage will drop low, the car tries to background charge, I stop it with the calpod. I use the pack around the 40% level and voltage pops up. After voltage pops back up, the car doesn't try to background charge as often... But that wouldn't happen if I didn't manually, purposely manipulate the car with the calpod, turning off the background charge and using the pack at a low charge state. Rather, the car would see the first low-ish voltage, the low-ish voltage on the first cycle down, and immediately start to background charge, charging until say 70% nominal. And it will keep doing this over and over, never letting the pack get used in even modestly low charge states...

The stock management appears to charge too much, too often, keeping charge state too high too much. I think this ends up 'crudding up' the lower charge states, makes them even less usable - higher resistance, voltage depression, whatever you want to call it.

I'm seeing something like 144-145V at about 20-25 amp discharge, at 62F, at around 40% state of charge. I can also invoke full assist and get it - somewhere around 70-80 amps at 125V, with these conditions... I used to think the BCM charged the pack to around 70-75% because the pack could only perform well, like put out full assist, when the pack was charged above say 60%. I don't see it that way at all, now... Being able to use the pack like the numbers above describe, to me used to be unheard of, it was impossible.

If you've ever seen discharge curves (voltage vs. time or capacity) for Insight NiMH cells, good ones are really quite flat over most of the discharge, while bad ones, mainly ones that have whatever kind of voltage depression/memory effect, crud, whatever, will crater early on, typically well before the mid point. It's this area of the capacity - the area between the mid point and the end - that, over time, gets used less and less in the Insight. And I think it's a negative feedback loop, too: the less this area gets used, the more deteriorated it becomes - and the less it will be used on the next iteration, and so on. But, I think, if you force usage at low charge states, I think it might keep the 'curve' high, keep it from cratering early. And then, the car allows usage of that area on its own more and more. To a point, at least (I think there's hard-coded behaviors, like fixed charge state percentages, that trigger stuff. For instance, at about 38% nominal, I don't think you get as much assist, regardless of voltage)...
 

·
Administrator
Joined
·
10,773 Posts
Your forcing your well balanced pack into the lower soc area which reactivates dormant material.

That's why deep discharging with lightbulbs etc works as well. It's basically the same thing but because of the low currents can be used with poorly balanced packs with a smaller risk of damage..

In the UK cvt rally car the stock battery always performed very well when given a real hammering and used until it was empty and then charged with tickover regen until full.

Exercising the pack over the full range is definitely beneficial.. Same for humans.. :)
 

·
Registered
Joined
·
6,157 Posts
Discussion Starter #3
Your forcing your well balanced pack into the lower soc area which reactivates dormant material. That's why deep discharging with lightbulbs etc works as well. It's basically the same thing but because of the low currents can be used with poorly balanced packs with a smaller risk of damage.
hmm, I don't think it's the same process/mechanism as low current deep discharge, though it could be similar and/or analogous in ways... The problems each method addresses - low current deep discharge and what I'm describing, just forcing usage of relatively lower charge state areas - seem different. What I'm describing seems to address 'damage' or 'dysfunction' or simply normal operation that's not carefully dealt with by the BCM. Deep discharge addresses longer term, deeper seated deterioration...

I'm suggesting that usage of even normally functional Insight NiMH cells includes 'hysteresis' that the BCM doesn't adequately handle or consider. Either that or some form of deterioration sets in very very quickly - that the BCM can't deal with appropriately... I'd guess it's a combination of the two. (Or, I guess it could be that my pack is old and newer packs don't behave like this - which I don't know since I've never had a new pack - and Honda just figured packs don't need to last forever)...

Over time, the "deeper seated" deterioration sets in - and that's when low current, I would say ultra deep discharge, is needed. The electro-chemistry that happens with that isn't the same as what would happen with simply using the pack at normal charge and discharge rates at merely somewhat lower charge states than the car usually sticks to. I mean, around 40% charge state isn't that low; it's simply lower than what the car normally pushes toward... But, it IS in a range - roughly below 50% - that seems to get 'eaten up' quickly in normal day to day operation. I've discharged sticks/cells after various forms of partial usage (i.e. not full cycles) and it seems par for the course that discharge curves will get depressed (voltage sag over the second half of the curve, mid point voltage happening earlier and earlier in the discharge)...

I'm not actually sure whether using the pack at lower charge states will preserve a normal, flatter, loftier discharge curve. I get the curve normal through ultra deep discharge; I'm thinking using the pack at lower than normal charge states will help keep it normal. I've been keeping it low for about half a year or so at this point, but it wasn't until now that I realized just how far I could take it, or rather, how much farther I could take it than I had been (I'm still not sure how low I can go; 40% seems about the limit, as 38% seems to have those 'hard-coded' nominal triggers)...

Either that or it's simply an interesting test: if one uses the pack around the 40% level day to day, rather than around 70%, without problems, without recals, etc., it's like you know your pack is good - because you can always let it charge up to 75% and - boom - you have another 35% of capacity to burn. You can purposely make the car use that low range, knowing you're on the edge, and it's easier to spot when or if failure starts to happen, too... In other words, I'm fairly sure that normal operation means a discharge curve that sags more and more, day by day. The BCM will force usage at higher and higher charge states - and that makes the problem even worse. If you can continue to use the pack around 40% day to day, you know your pack isn't suffering the degradation that heretofore has been par for the course - because if it were, you wouldn't be operating at 40%, you'd be getting neg recals. Or, you'd simply see voltage getting lower and lower, background charge kicking in incessantly, lower discharge currents, etc. etc...
 

·
Registered
Joined
·
630 Posts
Do you have any ideas on how to do such deep high rate discharging in a way that doesn't eventually blow a pack by inadvertently and repeatedly reversing a cell that turns out to be weak?
 

·
Registered
Joined
·
6,157 Posts
Discussion Starter #5
Do you have any ideas on how to do such deep high rate discharging in a way that doesn't eventually blow a pack by inadvertently and repeatedly reversing a cell that turns out to be weak?
Not sure what "deep high rate discharging" you're referring to. The only deep discharging mentioned has been low rate. And what I'm talking about isn't deep discharging...
 

·
Registered
Joined
·
6,157 Posts
Discussion Starter #6
I mentioned earlier that I wasn't sure just how low I could take charge state while still being able to bring voltage back up to the levels it was at at high charge states, due to 'hard-coded' stuff. I experimented more with that and it looks like around 36% or so, at least with my 305 BCM, is the limit. I could still get voltage back up to normal high levels (around 158 to 163V or so, down around 29% to 39%), but despite that, background charge wouldn't go away on its own, and more importantly, assist was throttled.

Basically, at around 36% it's very difficult to invoke assist - it takes much more throttle, so ICE is coming into play way more, plus the assist you get is feeble. I couldn't get full blown full assist - about 50 amps was the highest, at full throttle, despite a high voltage. Partial throttle assist would kick in at around 10-15 amps only, rather than around 20+ amps (it's very easy to invoke assist in 4th gear and hold a constant 20 amp discharge or so, with even very light throttle, while pack voltage hovers around 144V, so I'm very familiar with what usually happens)...

I recall it's been mentioned that different BCMs behave differently at this low end; I recall Eli at Bumblebee mentioning that something like the older BCMs don't throttle assist much if at all at the bottom. I'm tempted to install my really old BCM, I think it's an 010 with a really low serial number (that secondary number/code that the OBDIIC&C reads)...

One other thing I didn't mention that I'm wondering about, that I haven't really verified - is whether 'the top end' will actually fill-up normally after a lot of use at the low end. Earlier I said that if you're operating at the low end you always know you've got all that top end at your disposal - 'just charge back up and - boom - you've got another 35%' of capacity. But truthfully, when I go to charge up I could get 'premature pos recal' - a pos recal to 75% well before the true 75% mark.

In my head I'm envisioning that usage at the low end is preserving the flatness of the discharge curve, the loft in the mid point to lower part of the curve. When you charge ultra deep discharged cells (or deeply self discharged cells), voltage always goes high almost from the start and stays high. If you charge a cell or stick that's been used to some degree, voltage stays pretty low when you charge from empty and only gradually gets high. I've always wondered what that's all about. Seems like something closer to the 'charge after ultra deep discharge' pattern would be, better.

That's one thing I've seen during my low end experimentation, too: the more I've done this, the easier voltage seems to pop back up to the chemistry's equilibrium voltage (something like 1.318V per cell, so 158.16V for the pack)... Rather than seeing a somewhat unusual response to normal cells, it does seem like I could be seeing a somewhat unusual response to cells that are undergoing some kind of reconditioning... It just seems odd that it'd take this kind of use, after a year and a half of more or less normal use and some reconditioning stuff, to actually see a difference. I guess the main question will be whether it actually sticks; I've seen similar behavior before - not as clear cut and extreme, but similar nevertheless - but it has always been more or less transient. You drive, you use the pack, it warms up, cells 'get primed', they perform better. The next day you'd have to go through this whole usage scenario again to see the higher-level performance. Here/now I'm thinking the higher-level performance at such low charge states might actually stick around. What's more, I've seen higher performance at higher charge states as well - voltage stays higher longer, and more stable... Instead of seeing, say 145V at 20-25 amps at 70 degrees F, I might see 152V under the same conditions... Or even higher.

The basic question/scenario here has to do with that voltage hysteresis and whether different usage and reconditioning can produce a more favorable...voltage response. For instance, instead of voltage sagging and staying low after a relatively long assist event, voltage might stay higher longer and pop back up faster when it does drop low under load... I've described the way Insight NiMH works as being like a moving window - the usable capacity window moves around depending on where the NiOOH/NiOH2 interface is positioned in the cell, and its shape changes depending on - something, perhaps the 'cleanness' of the ionic pathways, the amount of electrolyte in the vicinity, et al. I wonder whether different usage can grow this window - make it bigger, make it stick around longer. It kind of seems like something like that must be happening when I'm seeing voltage stay higher longer but at lower charge states, and when I'm seeing higher voltages under load at higher charge states...

I'm pretty much a believer in what I'll call the 'mowing lawn theory of Insight NiMH', kind of what Peter described above. If you leave an area of your lawn un-mowed, it ends up growing in ways way different from the rest that you did mow. You gotta mow the whole thing if you want it to look the same. It's kind of the same way with Insight NiMH: if you want the cell to perform similarly over the whole charge state range, you gotta use the whole cell. Otherwise, areas of it will grow in different ways and end up performing differently... And this gets us back to why the stock battery management might be seriously flawed: one flaw might be that it concentrates usage in a very small charge state area (roughly a 10% window around, well, nominally 65% to 75%, but I think that tends to shift higher with time and degradation, so it ends up being around 75% to 85%. On the other hand, '75%' and '85%' - these values lose almost all meaning the way the stock management works, the way usage under this management slowly shrinks total capacity and concentrates usage higher and higher)...

To this there's just one bit I'll add: after this kind of degradation, the more serious problem might become uneven self discharge, at which point usage will be concentrated lower and lower, not higher. The higher charge states will languish/degrade because they're never used. Total capacity shrinks because you've got at least one cell that drains faster and hits the low voltage cutoff first and early, and then the other cells don't charge up as much because the high charge state degradation means high resistance, higher voltage, and hitting the upper voltage cutoff too soon...
 

·
Administrator
Joined
·
10,773 Posts
hmm, I don't think it's the same process/mechanism as low current deep discharge, though it could be similar and/or analogous in ways... The problems each method addresses - low current deep discharge and what I'm describing, just forcing usage of relatively lower charge state areas - seem different.
I think your method is just reaping the results of reactivating material and reducing depression etc.
Your exercising the pack and using power from low down soc and keeping awake material that would otherwise start to become lazy and depressed in the cars normal narrow soc window..

The normal way of doing it with low current discharge etc reduces the chance of reversal damage, and reaches deeper into the inactive material / depression to provide even more improvement in most cases..

I'm not saying don't do it if it produces results and is easy to do, but it may not be optimal.

As we know individual cell voltage measurement, and charge/discharge capability would be the ideal but it's impracticable.. :(
Then we would really know what is going on.. :)
Keep tinkering though..
 

·
Registered
Joined
·
6,157 Posts
Discussion Starter #8 (Edited)
^ Nah, I don't think you're understanding what I'm doing, what I'm describing. I don't blame you. I've already worked with this pack 'reconditioning'. I've seen what each stick does on the bench, I've examined each cell, etc...

[Later...] I think the most important aspect here is that, regardless of what reconditioning I've done, the pack is performing at a higher level only after I've circumvented the car's stock pack management. This is positive behavior/results that I would otherwise not be seeing.

The take away for lay folk is that they should probably be trying to use the pack at lower charge states, rather than letting the car keep charging the pack over and over again to high charge states and keeping usage within a narrow, high charge state window.

My sense is that stock battery management should have been engineered to use the pack in the middle, with cycling dipping down and peaking up from the middle, not perpetually focused in the higher 65%+ range... I've done a lot to this pack (and others) and I've driven with it with various usage patterns. But I've never forced such extended low usage before - and I've never seen the degree of improvement I'm seeing. Is it a coincidence - use pack at low charge state > see unprecedented improvement? Possible, but I'm pretty sure it's not...

Granted, this low usage follows on the heals of a tap-level ultra deep discharge, but I've done that before and I didn't see the degree of improvement I'm seeing now... Maybe the ultra deep discharge plus forced low charge state usage are working together... I mean, they do to a certain extent, as the ultra deep discharge is partially what allows the pack to be used so low in the first place. But I imagine whatever conditioning is happening by forced low charge state usage would take place whether one's pack were ultra deep discharged or not. Maybe. Or the flip side, whatever 'conditioning' (i.e. degradation) is happening normally with the car forcing usage in the high charge state window should be undone with intentional pack usage in the low charge state... I'm really leaning toward this side. It's not so much adding a positive - some 'reconditioning' - but rather, it's undoing a negative - circumventing the concentrated high charge state usage that the BCM imposes...
 

·
Registered
Joined
·
6,157 Posts
Discussion Starter #9
I was skimming through an old Panasonic NiMH Technical Handbook and came across a rather matter-of-fact statement - something I've seen before yet never fully appreciated - that supports the notion, explained above, that Honda's battery management is most likely flawed, maybe seriously so. If true it would explain why my pack performance continues to shine - as long as I manually thwart OEM management and force low charge state usage...

Pretty sure most BCMs don't allow discharging below about 132 volts, or 1.1V per cell (13.2V tap level). Background charge/forced charging usually kicks-in well before that or, if assist is in play, assist throttling ends up maintaining about 13.2V. If you go full throttle assist you can drop voltage to 120V/12V, but in general, the level trying to be maintained is 132V/13.2V. The problem with this is that discharge voltage characteristics suffer - you end up with voltage sag - if cells aren't discharged low enough. Panasonic says they should be discharged to 1V... This is age-old stuff - it's 'memory effect' and 'voltage depression', but here it is, plain as day, in Panasonic's own words:

"Discharge characteristics
The discharge characteristics of Nickel-metal hydride batteries are affected by current, temperature, etc., and discharge voltage characteristics are flat at 1.2V, which is almost the same as Ni-Cd batteries. Discharge voltage and discharge efficiency decrease proportional to current rise or temperature drop. As with Ni-Cd batteries, repeated charge and discharge under high discharge cutoff voltage conditions (more than 1.1V per cell) causes a drop in the discharge voltage, which is sometimes accompanied by a simultaneous drop in capacity. Normal discharge characteristics can be restored by charge and discharge to a discharge end voltage down to 1.0V per cell."

Certainly over time and usage our packs degrade due to this: Packs usually only get discharged to the equivalent of 1.1V per cell, cells never see this 'Panasonic restoration voltage' of 1V. It'd actually be worse if you drove at night all the time, where background charge kicks-in at a high charge state, or if you don't use much assist. I also think it can happen very quickly, though, perhaps more so or only with older packs...

Again, the takeaway is that, if you want your pack to last and/or to work better, you should be trying to force low charge state usage. Initially this may require that you do some kind of deep discharge/grid charge, because if your pack is imbalanced or too crudded-up you won't be able to take it low in the first place. But after that, I think something like, at minimum, a weekly low charge state usage drive, is needed to maintain pack performance.

Here's a link to a post that nicely sums-up the more technical, electro-chemical explanations for all this: https://www.insightcentral.net/threads/tinkering-with-a-non-working-ima-battery.81778/page-11#post-912394
 
1 - 9 of 9 Posts
Top