30kWh minimum cell voltage

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tomhanman

Active member
Joined
Apr 20, 2020
Messages
38
Hi, this is boring, but I'd appreciate any educated points of view.

I am the proud owner of an December 2015 30kWh with 100,000kms on the clock. Hey, I can hear you inhaling through your teeth with a pained expression on your face!

I've got the usual range anxiety, and a degraded battery, and the BMS "update" or as I like to refer to it the "get Nissan out of jail free card" was done years ago.

This is a picture of getting back to my workshop the other day having just triggered 🐢 mode.

That screengrab is reading 10% battery capacity remaining (yes gross capacity not useable but still) while I don't have a single cell above 3V. And have a third of the pack (center of rear stack per chance?) At 2.5V.

Is any of that normal? Any ideas greatly appreciated 👍

uc
 
That's a pretty high amount of unbalance between the cells from what I've seen. I'd say normal at 10% SOC would be something under 100mV although the unbalance usually gets worse at lower SOC % and your battery is somewhat degraded at 75% SOH.

Turtle mode is triggered by the lowest single cell since the BMS must protect any cell from going too high or low on its individual voltage to prevent damage or worse.

How do you normally charge? The BMS supposedly continuously tries to balance the cells and it may the case that your battery is just degraded far enough that the BMS can't keep the cells balanced but maybe several long slow charges to 100% SOC will help balance the cells.
 
tomhanman said:
Oh, so sharing from Google photos doesn't work then?

Yeah, Google photos isn't easy to share from although I think I've read somewhere that you can do some HTML level stuff to get it to work. Most people just use imgur or something similar.
 
Oh so the pic did work?
Wow, I couldn't see it so I changed the hosting... Still can't see it! Is it still there?

Thank you very much for getting back to me.

I usually charge at 4kW from my solar, and usually keep it between 20 and 80% but I use every damn percentage when I need to... They don't go very far! And I take it to 100% fully balanced at least once a month.

I agree there is a wide spread, But at such a low voltage I just don't see where the 10% is hiding, and I don't see why turtle didn't step in earlier. I thought that turtle mode showed up as the first cell reached 3V, not once they had all gone past it!

I mean 10% is 15km - nearly 10 miles. Well they've got to be having a laugh, 😂.
 
What I'm getting at, I suppose, is that it would be very handy for Nissan to be able to say there is still 10% in there because, as you say, that would mean I have the 75% capacity battery reported by the bms... Whilst if I actually had a 65% battery plus a software con (sorry, update) well then they would owe me a new one... I've got until December assuming the warranty is still valid without any service stamps.
 
AFAIK, All Nissan cares about is the number of bars on the dash and whether the BMS firmware update has been done. Having the big cell imbalance does reduce the usability of the car but unless it gets bad enough to throw a trouble code Nissan won't care.

I could see the picture by opening it in a new window. It didn't show up embedded in the post though.
 
Thanks Goldbrick. I believe I have now resolved the picture visibility thanks for SageBrush.

The battery always returns to being fully balanced by the time it is fully charged, so I guess it is not beyond the BMS yet and hence not in the realm of fault codes.

I'd like to hear from any other 30kWh owners about their cell voltages at low charge / turtle. And what percentage leafspy gives at that time.

If there are any brave 30kWh owners still out there?
 
Finally managed to get the picture to show up thanks to SageBrush's Tuto in another post. Not complicated at all!
 
Remember: it's all just a BMS programming error. That's what Nissan said, and what just about everyone was telling me, right up until Nissan started replacing lots of packs. There was even a shop someplace like New Zealand that proved it, with graphs and everything! :p
 
Hi Leftie,

Yes I remember the New Zealand pages. I think they did a great job, five years ago. But unfortunately it seems nobody continued their monitoring and indeed graphing! Then of course all those Leafs got sold on to maybe less militant owners.

Who knows the truth, maybe Ghosn, I'm sure he'd share!

But it seems from this statistically insignificant analysis that they have removed all cell protection buffer from the bottom end... Which would of course improve available capacity in the short term, and then lead to exaggerated cell degradation.
 
I would imagine that if it were just the BMS set too low, then there would be quite a few conservative, range anxiety-averse 30kwh Leaf drivers who still had great packs. Maybe it's no one factor, but several.
 
I currently own 2 30kWh Leafs. On both the BMS firmware update made a huge difference and I'm convinced there was a problem with the original firmware that was fixed by the update.

That said, the 30kWh packs do seem to be a weak spot for Nissan and I imagine as many of them approach 8 years old they will qualify for a warranty replacement.

In fact, that is why I bought the second Leaf. It was at 6 bars before the BMS firmware update so I took a chance that it would qualify for a warranty replacement. After the firmware update, it is now at 75% SOH. I don't know if it will reach the warranty threshold or not at this point so I may sell it immediately rather than risk having it drop the 4th bar just after the warranty expires.

On the second Leaf, before the BMS firmware update, the SOC% on the dash dropped very quickly to about 25% then just leveled out. By the time it hit 20% SOC or so, it was close to 'right' again but compared to my first Leaf (same year/model) the SOC% was whacko. After the BMS update it operates normally (about 1 mile per % SOC for my usual driving). This is not the GOM but the actual SOC% on the dash. I've put 30k+ miles on my original Leaf so I know how it should behave.

I'm convinced the original BMS firmware was buggy but I have no idea about the details of what changed.
 
Well Goldbrick, I too noticed an improvement in range 45,000kms ago! Now, in good weather, driving at anything up to 50mph I can manage about 90 miles on whatever is left in the battery, so a little less than you... But hills, etc will all play a part in that.

If by chance you should stumble upon turtle mode, try and send a leafspy screenshot so I can compare voltages.

That is what is really in my mind. I have never seen another EV showing 2.5V on cells and still driving!

Cheers.
 
I did run my Leaf down to 0 a few months ago. It died about 20 feet from my driveway and I had to push it in to get it close enough to reach the EVSE cord. I had LeafSpy running at the time since the dash was all --- but I can't remember the details except that it said I had about 1% SOC left when it quit.

I'll try to run it down to turtle again and get a screenshot, but it may be a week or two until I find time. I'm 99% certain my imbalance is not as bad as yours but I don't know the exact numbers.
 
It could be bad sensors or something that could be calibrated in the field to improve the performance but from the press releases and after getting it done twice, I think it was just a re-flash of the program that made the capacity calculations better. But I've never seen anything that actually specifies what changed or why it fixed the problem(s).

IMO, there's nothing evil in that since with the exception of Intel's floating point bug most companies never release details about firmware issues and/or their solutions to the public. And of course, that was not really firmware but it is quite similar.
 
It died about 20 feet from my driveway

That is impressive. If you'd got back without it stopping you'd never have known just how close you'd come.

it said I had about 1% SOC left when it quit.

That is interesting and makes perfect sense. Except that the story has always been that Leafspy shows total battery capacity whilst the dash shows useable. And It has always been a given that there is a difference, as with any self respecting EV allowing protection for the battery, top and bottom. 1% of a 75% capacity (I'm guessing at that as I don't know which you were in) is about 225Wh... That is, well, minimalist! Maybe I should have tried to set off home again to use the last 9%, but I can't see how without reducing the cells to double Alkaline voltages.

I'll try to run it down to turtle again and get a screenshot

That would be great, thank you. But at the same time, no rush, and really don't go out of your way. I was hoping there'd be loads of people out there with existing grabs from hairy moments in the past. It seems not so far.

I also don't think there's any evil in them not telling us what's inside the update, but since Dieselgate, I am rudely awakened to the idea that very large companies might be willing to make poor moral judgements in order to protect bottom lines. Especially considering what happened to VW after those poor moral decisions (basically nothing, no loss of market share or badge desirability) so why not!? Messed up.
 
Yeah, it was funny how close I was. I was literally next to my house but couldn't make the final corner into my driveway. I have to admit it is pretty embarrassing to have to push an EV home since it was dead, though. Sort of like the 'walk of shame' when you can't fix a flat tire on your bike for whatever reason.

Also, I knew I was in trouble for quite a while so I took the back roads home so in case something happened I wouldn't be in the middle of the highway. I thought that going slower might help although I think it was probably a wash due to snow, etc on the back roads compared to smooth pavement on the main route.

I'm curious myself now so I'll see if I can run it down this weekend. I don't know if I'll get all the way to turtle but I can certainly get down to under 5% SOC and I'll see what it looks like there.
 
Here is a LeafSpy shot of my car at turtle. The dash was at --- but LeafSpy shows the SOC at 9.3% even though the Ahr was at 8 GIDs or 2.2%. I think the Ahr reading is more accurate since the last time I got this low and got stuck it didn't last long after this point. In fact, this was a somewhat hair-raising experience since it went to --- at about 6% SOC on the dash so I had to scramble to find a charging station. The first 2 I found were dead (and the outdoor plug I found on an office building too - I was getting desperate....) but finally I found an active station that had 2 ports. There was a Tesla parked at one (unplugged) but the other was open. It was a vendor I never used before but there were instructions on the station and after I logged into the system with my phone I was able to charge for 30 minutes to get home.


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