62kw battery balancing

[Dave]

Hey, I got my second leaf, first one was a 2013 many years ago that I only had for a year, finally got another one, a 2020 sl plus
Had it about a month, still had leafspy pro from the first leaf.
Apparently the battery in this 2020 leaf had a few cells replaced under warranty 6 months ago before I owned it. I don't have any documentation for this.
Car gets great range, 95% soh, but a large chunk of cells are 70mv different.
Any ideas how to get this balanced?
I've read all the threads, left the car at 100% plugged in all night, no difference.
Thanks, Dave
Leafspy screenshot below....
https://ibb.co/NS4MTmS

 

[Learjet]

Had a module replaced and mine are set to balance at the lower SOC levels perfectly...my understanding is lower balance is more important to prevent early shutdown from a cell reaching the min. voltage before the rest of the pack...at a full charge my pack looks like this right now:

Click For Full-Size Image.


At lower levels:

Click For Full-Size Image.

 

[Dave]

Thanks, that makes sense, I haven't checked while it's been low. I'll try that!

 

[Learjet]

Thanks, that makes sense, I haven't checked while it's been low. I'll try that!

let us know...I'm curious to compare at lower levels

 

[Dave]

Will do. It will be a few days! I post an update.

 

[cwerdna]

You mean 62 kWh?

 

[Dave]

You mean 62 kWh?

Whatever....

 

[cwerdna]

You mean 62 kWh?

Whatever....

kW and kWh are totally different metrics. See https://mynissanleaf.com/viewtopic.php?p=450508#p450508.

https://www.mynissanleaf.com/viewtopic.php?p=564743#p564743 is a pointer to a cluster@$%$% that happens when someone doesn't know the difference. Back then, it was rumored the Model 3 would have an <60 kWh pack. And, Tesla was introducing per minute charging in places where they couldn't bill by kWh. They charged one price per minute for <60 kW charging and another one for >60 kW.

Just because a car has an <60 kWh pack doesn't mean it is limited to <60 kW charging but that guy reeler couldn't use the right units and get things straight, making discussion impossible.

Perhaps watching the video at https://electricrevs.com/2018/07/17/watch-a-bolt-ev-at-a-chargepoint-express-250-charge-at-up-to-55-kw/ would give you more context. Or maybe skip to 6:38 of https://insideevs.com/news/495913/nissan-leaf-dc-fast-charging-curve/, watching power level (in kW) vs. energy dispensed in the upper right (kWh).

 

[Stanton]

Had a module replaced and mine are set to balance at the lower SOC levels perfectly...my understanding is lower balance is more important to prevent early shutdown from a cell reaching the min. voltage before the rest of the pack...at a full charge my pack looks like this right now:

Unfortunately, the replacement cells were installed at a lower value than the rest of the pack, so you can "cook" the rest of your pack all you want...but you won't ever get that new module to match. I have similar situation (although only ~80mV difference), but I installed the replacement cells at a higher value; it's been a very slow path to balancing for me.
Having said all that, you still look OK at the bottom end, which will keep you from an unexpected shutdown...but you will probably never be able to get "full capacity" from your pack. At least (in my case), I can live without those extra few miles.

 

[Dave]

So it makes sense, the cells that have been in the vehicle for 3 years have a lower capacity now than the new cells. If they were all balanced at low voltage the older cells will reach full voltage first. The balancing circuit will never keep up with the difference in capacity, so there will always be an imbalance somewhere....

 

[Learjet]

Had a module replaced and mine are set to balance at the lower SOC levels perfectly...my understanding is lower balance is more important to prevent early shutdown from a cell reaching the min. voltage before the rest of the pack...at a full charge my pack looks like this right now:

Unfortunately, the replacement cells were installed at a lower value than the rest of the pack, so you can "cook" the rest of your pack all you want...but you won't ever get that new module to match. I have similar situation (although only ~80mV difference), but I installed the replacement cells at a higher value; it's been a very slow path to balancing for me.
Having said all that, you still look OK at the bottom end, which will keep you from an unexpected shutdown...but you will probably never be able to get "full capacity" from your pack. At least (in my case), I can live without those extra few miles.

Did a full charge and long trip this weekend...loss of max range is minimal...maybe ~10 miles since new...still trying to estimate the loss over several long trips.

 

[Dave]

Update,
Got the leaf down to 28% and the pack was at 18mv difference https://ibb.co/Lhk62Jt
Took a reading at 68% and it was 60mv difference https://ibb.co/s5YTQms

So I can only assume the pack will be balanced when the Soc is 15% or so.
Makes sense considering the new cells are effectively a larger capacity that the 3 year old cells.

 

[johnlocke]

OK, I've got an oddity here. Ever since I bought the car, I've had one low cell. At full charge it's 72-74mv lower then the other cells which are within 10mv of each other. As the battery discharges the discrepancy shrinks to maybe 24mv at 15% charge. I've discharged down to 8% several times and I've also tried to charge the battery several times in row to try and improve the balance with no luck. Doesn't really seem to any effect on range but it drives me a little nuts when I see just the one cell low. Does anyone else have a similar problem? I know that this isn't something I can complain to Nissan about but I'm curious if it's unique or unusual.

 

[Dave]

OK, I've got an oddity here. Ever since I bought the car, I've had one low cell. At full charge it's 72-74mv lower then the other cells which are within 10mv of each other. As the battery discharges the discrepancy shrinks to maybe 24mv at 15% charge. I've discharged down to 8% several times and I've also tried to charge the battery several times in row to try and improve the balance with no luck. Doesn't really seem to any effect on range but it drives me a little nuts when I see just the one cell low. Does anyone else have a similar problem? I know that this isn't something I can complain to Nissan about but I'm curious if it's unique or unusual.

Seems like your kinda in the same situation im in. One of your cells, many of mine, are of a higher capacity than the other cells in the battery.
The cells have an effective voltage from about 2.9 - 4.2volts, and the capacity is determined by the physical size, chemisty and age of the cell.
In my case, most of the cells are 3 years old and have lost some capacity, the cells that were replaced have the original new capacity. Since the balance circuitry in the leaf can only dissipate small amounts of power relative to the cell capacity, the pack can only be balanced at one voltage.
My pack, while charging, would always have to bleed current from the new cells because the older, lower capacity cells will be at full charge sooner. The balance circuit would have to bleed way more power that it is capable of turning it to heat, which is not good.
So, if the pack is balanced at some voltage, high or low state of charge, there is no problem if your range etc is good.

 

[Stanton]

OK, I've got an oddity here. Ever since I bought the car, I've had one low cell. At full charge it's 72-74mv lower then the other cells which are within 10mv of each other. As the battery discharges the discrepancy shrinks to maybe 24mv at 15% charge. I've discharged down to 8% several times and I've also tried to charge the battery several times in row to try and improve the balance with no luck. Doesn't really seem to any effect on range but it drives me a little nuts when I see just the one cell low. Does anyone else have a similar problem? I know that this isn't something I can complain to Nissan about but I'm curious if it's unique or unusual.

Short answer: you are on the way to having a bad cell/module that will eventually limit your range.
Long answer: that's the same way I started out. I had a weak cell that was consistently ~70mV lower at full charge...then 100mV...then 140mv (over a period of weeks). Luckily it was only one cell/module, so I "bit the bullet" and replaced it. You can search for my posts in other threads, but long story short it's not something Nissan wants to do (I basically did it on my own)...and not cheap (finding a good replacement module is only half the problem). But I'm very glad I did it.
Don't shoot the messenger.