The 62kWh Battery Topic

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DaveinOlyWA said:
I have one cell that strays from the pack and has from day one. It is a bit "different" as the delta is greater at higher SOC and not noticeable in the mid SOC range.

All of mine, the difference was always at the bottom end, as it got closer to the 0% SOC, the gap of those cells would widen and widen until finally they were the ones close to hitting 2.5V while all the others were still in the +3.2 range, which depending how much capacity was left, it could in theory bypass the turtle mode and just go straight to shutdown. My wife's 2018 did exactly that in the first gentle deep discharge I did on her pack, caught me by surprise since the pack was suppose to have at least 1.7 kWh remaining, no turtle mode, straight to pack shutdown. :shock:
 
knightmb said:
Learjet said:
another drop and that pesky cell keeps dropping :(
Yeah, I had the same issue on mine when I bought it, but it was cell #3, doing the same thing, always way off in voltage from the others. It took about 2 gentle deep cycle discharges to finally get it in line. My wife's 40 kWh Leaf had the same issue with a lot of random cells, took 3 gentle deep cycle discharges to finally get her cells into shape.
What was the max mv delta after your ministrations ?
 
SageBrush said:
knightmb said:
Learjet said:
another drop and that pesky cell keeps dropping :(
Yeah, I had the same issue on mine when I bought it, but it was cell #3, doing the same thing, always way off in voltage from the others. It took about 2 gentle deep cycle discharges to finally get it in line. My wife's 40 kWh Leaf had the same issue with a lot of random cells, took 3 gentle deep cycle discharges to finally get her cells into shape.
What was the max mv delta after your ministrations ?

Mine is half-way down, middle of that page here: https://mynissanleaf.com/viewtopic.php?f=9&t=30585&start=910
I think it was 12 mv last time I did a quick check for that update.
Before I did anything, Cell #3 was always about 150 to 200 mv off from the rest of the pack.

My wife, her Leaf is on this page. https://mynissanleaf.com/viewtopic.php?f=9&t=25773&start=1210
Near the top of the page, her battery was doing nice at 4 mv
My wife, her battery had 4 or 5 different cells, don't remember the exact numbers, they would be off by 250 mv or more, quite all over the place really.
 
Well, the SV+ had its battery update (now 2 1/2 years old) and down another .63%. It's now 90.73% SoH. While my last double 100% charge to leave on this last trip the day before adjustment likely didn't help, It's curious to see the divergence vs. The S+.

Not related, here is the battery temp for 3 of the 5 legs of my last trip. Interesting that over the 2 hours from Lafayette to Bloomington, the battery only lost 4.2F on the top end (even with dropping temps). The bottom dropped faster. It will be interesting to compare to my S+ when we do the Kansas run. (Middle of the chart).

https://drive.google.com/file/d/18M-bv4UevOKDmyCR9COS6kK6A_NnpJpJ/view?usp=drivesdk
 
DougWantsALeaf said:
Well, the SV+ had its battery update (now 2 1/2 years old) and down another .63%. It's now 90.73% SoH. While my last double 100% charge to leave on this last trip the day before adjustment likely didn't help, It's curious to see the divergence vs. The S+.

Not related, here is the battery temp for 3 of the 5 legs of my last trip. Interesting that over the 2 hours from Lafayette to Bloomington, the battery only lost 4.2F on the top end (even with dropping temps). The bottom dropped faster. It will be interesting to compare to my S+ when we do the Kansas run. (Middle of the chart).

https://drive.google.com/file/d/18M-bv4UevOKDmyCR9COS6kK6A_NnpJpJ/view?usp=drivesdk

Pack is probably getting flabby from lack of exercise. I have often wondered where my pack would be right now had I stayed at my previous job? I would be over 60,000 miles by now. My 2016 S30 was at 100% SOH when she murdered just short of 30,000 miles in 14 months...

I wouldn't sweat it if I were you. Its my guess you will be within 1-2% of everyone else 2 years from now.
 
It is time to post results from my latest discharge test:
LEAF 2019 Battery Information 5.jpg

The car was parked at the airport from 10/13 through 10/30 so the 90-day update happened while it was parked. It lost 1.06 AHr while parked. It was a cool morning during the drive to the airport and ambient temperature was higher when I returned so the battery was cooler when parked (after 25 miles mostly freeway driving) than after sitting for over two weeks. The difference between 465 and 450 Gids indicates that about 1.2 kWh was used by the car while parked so it could be parked for a long time without significantly discharging the traction battery.
AHr 161.55 160.49
SOH 91.58% 90.98%
Hx 92.21% 92.21%
V 363.71 364.82
QC 12
L1/L2 254
Miles 37,998
Gids 465 450
Battery 69.6F 78.1F
Temps 71.1F 77.7F
71.2F 77.9F
Date 10/13 10/30
Time 0457 2304

Even though it lost 1.06 AHr and 0.6% SOH while parked, the energy storage capability of the battery was almost the same on 11/5 as 8/7.
 
GerryAZ

During my SV+ drive to Bloomington IN and back (a bit over 500 miles), I left just as an adjustment was taking place. I had plugged back in a couple times at 100% thinking it was giving me a couple additional gids before leaving. What I noticed was that the first handful of gid disappeared in the first partial mile. Similar to your note below, this suggests that the bms is really adjusting the SoH/Ahr to the real usable capacity and not managing a buffer as is sometimes speculated.

What we can't account for is how a significant SoH increase could happen. For a couple board members 2%...unless the bms can understood hard on a previous cycle (cold battery?).

Thanks for the update.
 
A BMS with a self preservation slant makes sense in some circumstances. The charging to 100% has a huge variance in how the pack reacts ranging from very bad to very good. Part of it could be rationalized with heavy use requiring more full charges but the time at high SOC being minimal because of the heavy use.

Gerry's case (with a handful of others) is interesting due to his extreme climate. Previous packs wilted quickly in lesser extremes but his has not strayed from the pack. Now we do have our one exception; the guy in Palm Springs who lost his first bar at roughly 1/3rd the miles of anyone else but then again, I feel (like many others) that he isn't telling the whole story.

Another thought that has crossed my mind is Nissan instrumentation itself. Beginning to wonder how good it is and whether readings would be consistent across different vehicles of same trim, year, pack, etc?
 
Dave

One other curiosity is that post the long trip, the car seemed to be mildly more efficienct to drive. It is certainly anecdotal, but curious if Hx is connected to pack efficiency at all.
 
I still believe Hx is inversely related to internal resistance. Since temperatures have cooled a bit, I have less regeneration available immediately after full overnight charge than I did when the car was newer. It is not an issue, just an observation that there is slightly less regeneration near full charge. As I have stated before, most of my charge cycles are from a low SOC to 100%. I try not to leave the car at full charge for more than a few hours, but it may sit as much as 6 to 8 hours if something happens to prevent me from driving first thing in the morning.
 
GerryAZ said:
I still believe Hx is inversely related to internal resistance. Since temperatures have cooled a bit, I have less regeneration available immediately after full overnight charge than I did when the car was newer. It is not an issue, just an observation that there is slightly less regeneration near full charge. As I have stated before, most of my charge cycles are from a low SOC to 100%. I try not to leave the car at full charge for more than a few hours, but it may sit as much as 6 to 8 hours if something happens to prevent me from driving first thing in the morning.

Which is the case for Leaf gen 1, i.e. Hx is battery conductance which deceases as the battery ages. The battery becomes less efficient with age.
Leaf gen 1 data indicate that SOH and Hx are positively correlated.
 
GerryAZ said:
I still believe Hx is inversely related to internal resistance. Since temperatures have cooled a bit, I have less regeneration available immediately after full overnight charge than I did when the car was newer. It is not an issue, just an observation that there is slightly less regeneration near full charge. As I have stated before, most of my charge cycles are from a low SOC to 100%. I try not to leave the car at full charge for more than a few hours, but it may sit as much as 6 to 8 hours if something happens to prevent me from driving first thing in the morning.

To add to that; I charged to 97% in anticipation of a trip to make but the time was pushed back a few hours so ended up getting some town errands done. I was down to 88% SOC before I showed full regen capability. I have yet to view the logs to see if the difference is significant but most of the charge I did was on DC so pack was "warm" in the mid 80's so was expecting full regen back by the low 90's. My initial thought was the change was due to degradation since I am about 4-5% lower SOC than during my previous measurements.

The other thing is short stints on DC and AC is not enough to warm the pack so pack temps are now spending most of their time in the 60's which has greatly slowed the daily .01% drop from 2-3 times a week to slightly less than once a week.
 
DaveinOlyWA said:
Another thought that has crossed my mind is Nissan instrumentation itself. Beginning to wonder how good it is and whether readings would be consistent across different vehicles of same trim, year, pack, etc?

This article says the analog front end for the Gen 2 Leaf is a Maxim IC.
https://www.maximintegrated.com/en/aboutus/newsroom/2018/nissan-integrates-maxim-battery-monitoring-ic.html

Digging on their website shows 4 publicly advertised BMS chips. Depending on which is used, the rated accuracy would be +/- 10mV (MAX17823B) or +/- 6mV (MAX17843) or +/- 4.5mV (MAX17852 and MAX17853) per cell across voltage and temperature. Or it could be a custom part that's not advertised, but I'd still expect similar accuracy.

That's just the analog front end. We don't know what sort of fuel gauging algorithm is used. Even with a perfect voltage measurement, it's not a simple thing to calculate SoC. The only two points that are well known are the 100% when end of charge occurs and 0% when the empty detection occurs. Any other point is an estimate based on predicting when the system expects full and empty detection will occur.

At mid-range, SoC is most difficult to determine with accuracy since you're far from the known points (coulomb counting drift has accumulated) and there's a pretty small slope in voltage vs. charge state (voltage based estimates are less accurate). I've seen my end-of-drive efficiency summary vary quite a bit depending on what battery range I'm operating in. My guess is that the SoC calculation error is showing.

But regardless of the error of the BMS system, it will put the car in turtle mode when it thinks the battery is low. So long as the BMS estimate of empty is conservative, the BMS estimate of empty will occur before true empty detection (this seems to be true for the Leaf, so long as no cells are "bad"). Meaning that the BMS estimate of empty might as well be considered true empty because it will limit vehicle function.
 
Snargleblarg said:
DaveinOlyWA said:
Another thought that has crossed my mind is Nissan instrumentation itself. Beginning to wonder how good it is and whether readings would be consistent across different vehicles of same trim, year, pack, etc?

This article says the analog front end for the Gen 2 Leaf is a Maxim IC.
https://www.maximintegrated.com/en/aboutus/newsroom/2018/nissan-integrates-maxim-battery-monitoring-ic.html

Digging on their website shows 4 publicly advertised BMS chips. Depending on which is used, the rated accuracy would be +/- 10mV (MAX17823B) or +/- 6mV (MAX17843) or +/- 4.5mV (MAX17852 and MAX17853) per cell across voltage and temperature. Or it could be a custom part that's not advertised, but I'd still expect similar accuracy.

That's just the analog front end. We don't know what sort of fuel gauging algorithm is used. Even with a perfect voltage measurement, it's not a simple thing to calculate SoC. The only two points that are well known are the 100% when end of charge occurs and 0% when the empty detection occurs. Any other point is an estimate based on predicting when the system expects full and empty detection will occur.

At mid-range, SoC is most difficult to determine with accuracy since you're far from the known points (coulomb counting drift has accumulated) and there's a pretty small slope in voltage vs. charge state (voltage based estimates are less accurate). I've seen my end-of-drive efficiency summary vary quite a bit depending on what battery range I'm operating in. My guess is that the SoC calculation error is showing.

But regardless of the error of the BMS system, it will put the car in turtle mode when it thinks the battery is low. So long as the BMS estimate of empty is conservative, the BMS estimate of empty will occur before true empty detection (this seems to be true for the Leaf, so long as no cells are "bad"). Meaning that the BMS estimate of empty might as well be considered true empty because it will limit vehicle function.

Well, the LEAF uses two key metrics for low battery issues.

The ONE thing that has been all but perfect is the GID count verified probably thousands of times here and elsewhere in Electron land. It was 24 and 48...sometimes 49 on the 30's. Then larger capacity batteries came in and well, consistent but not the same super tight grouping of results. This can't be done using voltage.

The other is voltage. Low voltage processes only need a single cell to hit the parameter and you have Turtle or Shutdown. Interestingly enough, Turtle can be circumvented if you are smart about it which is code for not trying to make it the last 3 miles with an estimated ½ mile of range left.

The other thing is the capacity estimates. I am sure Nissan uses the a basic algorithm with changing SOC, voltage, current, etc. which over time can closely approximate the capacity of the pack. Its interesting to me that the reset process completely wipes the slate and even in extreme cases of packs with several lost capacity bars; can still take weeks or even months to get "close" again.
 
100% charge right before a lot of driving...still dropping...

BIpcZgbl.png


0KP3YaDl.png
 
DougWantsALeaf said:
At what size delta does it start to cause problems for the pack?

@100%, its not. Still managing to get 98.3% of available storage. What is it at 20% SOC is the problem. A low cell like that will likely prevent you from accessing the bottom of the pack effectively. Early Turtle, or worse a premature shutdown that will require time on the side of the road and a battery reset to "fix"
 
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