Here's a graph that illustrates what I'm proposing; I've posted it elsewhere before:
Nearly every point falls along a line that corresponds to 65mAh per percentage-point of capacity/state of charge. The ones that don't fall on the line are either instances when the data logged was insufficient (too small a change for the calculation) or related to the 72% positive recal hanging point, when most of the time it takes more than 65 mAh per percentage-point to move from 72% to 75% SOC.
I'm pretty sure it calculates state of charge most of time just as I explained it: a fixed capacity of 6500mAh and keeping track of amps-in and amps-out. I would describe it as having additional routines or algorithms to deal with the times that the straight forward calculations don't 'add up'...
I would tend to agree with you on the "standard" battery capacity of 6500mAh as well.
Observing the actions of the SOC after an over-night trickle charge, and then also watching the real-time battery voltage while driving, tends to support this theory, at least with my current battery pack, and being only about 1/2 "full" capacity.
About one year ago, when my battery was in better health, the SOC would pretty reliably track the true battery voltage very closely, until the voltage got to about 142ish or so.
I'm not sure to what extent or in what manner voltage plays in state of charge. It's not "no role" as some people say, but it's not linear, one-to-one. For instance, after a grid charge when I more or less know the battery is 100% full, and after just a little discharge, voltage can drop below the level that the IMA typically establishes as the '75%' level. Basically, a resting voltage of 165V, for example, is not always the same state of charge. Changes in voltage do seem to be a bit different, though, after grid charge versus normal circumstances.
Part of what I see could be the result of a weak battery though; a weak battery's voltage simply doesn't behave like a new battery, dropping more, rising more, for instance, under various loads. This probably complicates the IMA's interpretation of state of charge. Just yesterday I again saw something I've never seen before: a positive recal to 75% at an unusual state of charge (something like 66.6%). This was not after a negative recal. This is partially related to my grid charging, partially related to me resetting SOC from 95% to 75% a few days ago. I think it might have to do with higher voltages in a weak pack compared to a normal pack; voltage does play a role in the BCM's state of charge decision, and when it sees higher voltages due to say high internal resistance, it might think erroneously that the pack is fuller than it actually is, as so positively recal from say 66.6% to 75%...
Everything battery management related behaves just a bit differently after a grid charge to 100%. The last time I grid charged like this, the IMA (BCM or whatever) drained about 5% capacity the first couple days or so at the positive recal point (72%): it normally takes 195mAh to move 3 percentage points of SOC, from say 74% to 77%. And then, it normally takes about 300-500mAh to positively recal from 72% to 75%. After this grid charge, it took almost nothing to positively recal from 72% to 75%, effectively wiping out 3% of state of charge. In fact, it positively recal-ed from 70.2% to 75% one time.
After my last grid charge I let the car drain-off about 5% state of charge on it's own before I reset the state of charge with the OBDIIC&C. When I hit the positive recal point at 72% it did NOT take nothing to move from 72 to 75; it actually took a little more than you'd expect for the move of 3 percentage points, about 250 mAh each of a handful of recal events. But, yesterday it seemed to be charging much more than I would've expected given what was probably still a high true state of charge - and then after I dropped the state of charge down pretty low (55% or so) and started to charge back up, it positively recal-ed at about 66.6%. And yet, by the end of my journey, after all this charging, draining, positive recals and such, the net amps left me just about where I started; I started at about 75% state of charge, and after about 6000mAh of discharge and 6000mAh of charge, positive recals, etc. I was back at about 75% state of charge.
So, point is, at one leg of the journey it was overcharging, and then after another leg it under charged, and the end result was just about where it should have been, that is, based on amp-hour counting alone.
The/A question is, what's determining the positive recals, which is synonymous with the criteria that the IMA uses to establish a 75% state of charge level? There's not one state of charge threshold, such as 72%, where the car moves into its calibration routine; it happens in at least a few places, if not anywhere depending on wholly other parameters. It could be pack or sub-pack pair voltages under load - which would probably be higher in weak packs/sticks and thus in weak packs you'd get positive recals sooner than you should. It could be an ongoing accounting of net amps. Could it be individual thermistor-related - 1 of the 4 thermistors registers a change in temperature above and beyond the others? Time could, or likely, plays a role. Etc etc. I think it's a combination, mainly the net amps accounting, either sub-pack pair or pack voltages under load, and time...
As far as 6500mAh capacity is concerned, that's like the theory of evolution for me: it's virtually a fact. I have to think about that it terms of what you'd expect from a higher capacity pack, like the MaxIMA, and see if the results wash. In other words, if the BCM is operating as if the total pack capacity is 6500mAh, and you put in an 8000mAh pack, how would it behave, how would it treat the pack? Voltages, voltages under loads, should be the same. The only difference is that extra 1500mAh. Off the top of my head, it seems like the amp-hour counting/accounting will result in the 8000mAh pack not being at the state of charge that the car thinks it's at; "75%" won't be 75%; it might be 80%...
We know that the BCM is capable of using more than 60% of 6.5Ah because of the parallel packs and such. The BCM hangs at 28%(3 bars) while it waits for a voltage tap to become empty just like it hangs at 72% while it waits for a voltage tap to become full. But that may be inconsequential to what you're talking about, since you're still basically using the whole range of dash SoC gauge. Though even with a healthy stock battery, the BCM SoC will hang at 28% for a bit. But yes, it does seem the dash SoC is basically hard coded to represent 60% of 6.5Ah, or 3.9Ah(65mAh * 60).
When I did the original MaxIMA test, I got 60% of 8Ah out of the pack, or 4.8Ah.
I believe Peter has mentioned the upper limit seems to be about 10Ah based on his lithium system testing, which is why the BCM Fooler etc was needed.
There really is no question about where negative and positive recals come from:
It's true that voltage isn't a good determination of SoC, except at the upper and lower ends. We know the maximum voltage the BCM allows is 192V and the minimum it allows is 120V, which is 1.6V and 1.0V/cell respectively. These are standard NiMH voltage cutoffs under high loads.
I've noticed that you've mentioned ~180V as the upper limit a few times, which is incorrect. It is likely you have a subpack pair that is bouncing off the 19.2V limit with the whole pack at only 180V.
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My Insight has been having this same problem over the past few weeks. I noticed that the SoC gauge was showing all 20 bars lit , something that has only happened about three times before during 3 years of ownership. I was curious when the SoC did not drop below this level despite three short journeys to work so i connected up the OBD gauge on a slightly longer trip and was astonished to see the SoC climb to 99.6%. I had not been aware of this glitch but concluded it was somehow connected to outside temperature -the colder it is the higher the SoC will climb. Unfortunately the forum has been logging me off only a short time after logging on for months now so i could not post about it . By coincidence i was searching the forum again tonight for any previous posts about this problem when this thread appeared ; i am very relieved that this is not unique to my Insight . If it is of any help to diagnosing what the problem is the only change to the car made this year was having a Better Battery fitted about 8 months ago. This battery has not shown any signs of problems since it was fitted .
...I've noticed that you've mentioned ~180V as the upper limit a few times, which is incorrect. It is likely you have a subpack pair that is bouncing off the 19.2V limit with the whole pack at only 180V.
Not intentionally. It's just hard to keep everything straight, write about 'larger, sweeping' concepts without getting bogged down in the details... 180V seems to be the upper 'throttled' limit in my car. The IMA throttles back current to keep it at, or just around, 180V. That's the same as 120V for the bottom. But I've seen as low as 109V at the bottom, as I've seen as high as 191V at the top. These are very short-lived... But yeah, maybe I do have a sub-pack pair that's bouncing off the limit and it just makes it look like 180V is the throttled limit...
We'll have to talk about the MaxIMA and larger capacity packs later. I was saying, off the top of my head, that if the BCM is programmed to a pack capacity of 6500mAh, which I'm about 99.5% sure that it is, an 8000mAh pack showing 75% state of charge might actually be at 80% SOC - because 25% of 6500 is 1625mAh, whereas 1625mAh is only 20% of 8000.
If you grid charged an 8000mAh pack up to 100% with the key on, how much would the IMA let it drain? -- assuming that with a 6500mAh pack it would drain down to about 75%, like it does when I take it up to 81% with in-car charging. I did grid charge the stock pack up to 100% the other day with key on and the IMA does indeed drain it down, though I stopped it after only 5% drain. I presume it might go down all the way to about 75% if I let it...
Anyway, overall I'm not questioning whether the car would or would not let the user take advantage of the extra capacity. I haven't thought enough about it yet...
A simple test to see how the car treats a larger capacity pack would be this: get the state of charge up to a nominal 78%, reset the amps counter, discharge it down to 73%, write down the net amps, divide net amps by 5. My 'theory' says the result will be about 65, which would suggest that battery management is going on as if the pack were 6500 rather than 8000... Again, that's not to say that other management strategies wouldn't allow the user to take advantage of the extra capacity; just that the ongoing accounting and the displayed SOC is likely to be off...
Yeah, I would agree with that overall assessment. Fortunately, Honda seems to have left open the ability for seamless upgrades without significant software changes. The BCM seems to be very adaptive and definitely seems to know there is a very healthy pack under the hood quite literally the instant it is put in. I am pretty sure the MCM interprets the condition of the battery on the fly based on it's voltage fluctuations and this is what the SoC gauge is based off of. There's probably also some "fuzzy logic" in there to vary the time intervals etc. But it seems the MCM needs no "experience" with a battery to know that it is good. The SoC gauge behaves like it does with a new battery immediately upon installation of the new battery.
An interesting experiment would be to drive on an old pack, then insert a new pack without resetting the computers and see how it behaves.
I also believe that the BCM keeps track of battery cycles and has routines based on these cycles. I've seen evidence that the BCM will charge the battery to different SoC levels at different times as well.
It even states in the manual, regarding this original BCM cold weather bug, that occasional overcharging is good (for NiMH cells), but too much wears them out prematurely.
So to characterize the BCM as some simple, stupid computer that can barely manage a pack is a pretty bad characterization. There is no way that a battery would last 10-12 years if this was the case. There is far, far more going on in the background than we've even begun to realize, I'm afraid.
I'm going to set out on the task of logging a years worth of IMA data to a 16gb SD card soon.
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Another odd episode this morning: I had an IMA light. I had assist/regen and lean burn that worked as it usually does. I also had a P1444 code showing on the OBDII C&C. Before I left to come back home, I unplugged my grid charger (unplugged the connection to the harness) and all the codes/lights were gone when I started the car. When I got back home, I plugged the charger back in and the code/light didn't return.
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Warm air mod
EPS fuse removed
FAS/fuel injector interrupt circuit
OBDII C&C gauge
...It's true that voltage isn't a good determination of SoC, except at the upper and lower ends. We know the maximum voltage the BCM allows is 192V and the minimum it allows is 120V, which is 1.6V and 1.0V/cell respectively.....It is likely you have a subpack pair that is bouncing off the 19.2V limit with the whole pack at only 180V.
According to that diagram up there and what you say, the BCM fills up the pack until at least 1 sub-pack pair reaches the voltage limit - you say 19.2V. But how does that correspond to a 75% state of charge, and not a 100% state of charge (or thereabouts)? If all the cells are just about balanced, then theoretically the sticks should all be reaching that upper voltage limit at about the same time. How would that produce the 75% state of charge level?
You (Eli) often say that the BCM waits for a sub-pack pair (voltage tap) to fill up at the 72% hanging threshold, after which the state of charge is recalibrated to 75% (or whatever, sometimes 80% with some BCM versions). But what does a full sub-pack pair have to do with 75% state of charge?
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