Leaf range after battery module replacement

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nlspace said:
You have an incorrect assumption--that the BMS balancer pulls current from one cell to charge another.

The bleed resistors (430 ohms) on the LBC board can only burn off excess energy of a higher cell to bring it down to the level of the lower cells. The ASIC chips have internal transistors that provide the switch path for the balancing control of each individual cell in the 4-cell groups that each chip monitors and controls.

There is no shuttling of charge around the board from high cells to low cells.
Click to expand...

Yes, if that's how it works, I misunderstood for sure. If it's bleeing the charge off, the best case scenario is a high level SOC (higher voltage = higher bleed at the same resistance) for a long period of time.

If you want to try to balance it with the BMS, charge the car to 80%, leave it running in the garage at minimum power draw (with no heat/AC, etc) for hours until it gets to about 40%, charge via L1, and repeat until balanced. May take many cycles.

Again, I recommend that gary take the car back to the dealer and have it serviced properly.



Edit: Some quick math: 430 ohms at 3.7v = 0.032W power draw. Given a rated capacity of 56 AH, and assuming that the battery is 30% overcharged beyond the other cells (based on the range drop), that's a total of 16.8 extra AH in the battery. At a voltage of 3.7V, that's 62.16 WH in the cell. At .032W balancing draw, the car should fix itself after 1942 hours of operation--80 days nonstop.

Feel free to correct my math. If it's correct, I wouldn't want to rely on the BMS to balance those cells. Take the car to the dealer and have them fix it correctly. :)
 
Looks like a piss poor job of matching cells to the existing pack. Give it time, they will eventually self balance. Will likely take at least a month though.
 
Edit: Some quick math: 430 ohms at 3.7v = 0.032W power draw. Given a rated capacity of 56 AH, and assuming that the battery is 30% overcharged beyond the other cells (based on the range drop), that's a total of 16.8 extra AH in the battery. At a voltage of 3.7V, that's 62.16 WH in the cell. At .032W balancing draw, the car should fix itself after 1942 hours of operation--80 days nonstop.

Feel free to correct my math. If it's correct, I wouldn't want to rely on the BMS to balance those cells. Take the car to the dealer and have them fix it correctly.
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This gibes with what has been stated elsewhere: that the BMS can only manage balancing when there isn't a huge difference in cell voltages. I hadn't realized that this was one of those cases. It would be interesting to see if it would happen eventually with this Leaf, but the best course of action for the OP seems to be to take it back - and warn them not to "fix" it by keeping the car for months of joyrides and L-2 charges.
 
DaveinOlyWA said:
Looks like a piss poor job of matching cells to the existing pack. Give it time, they will eventually self balance. Will likely take at least a month though.
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Yes, but as per my math in an earlier statement, it'll be 80 days of operation (charging or discharging). With typical usage, this could be 2-4 years.
 
LeftieBiker said:
This gibes with what has been stated elsewhere: that the BMS can only manage balancing when there isn't a huge difference in cell voltages. I hadn't realized that this was one of those cases.
Click to expand...

This is the "problem" of lithium batteries. Unlike alkaline, they have almost a flat discharge curve before they fall off quickly. A small voltage difference seems like nothing at all--in reality, it can be quite a bit of capacity.

That said, you're also right. While the owner noticed a 30% reduction in range, that should have been 200mv of delta, not 60mv[1]. It's possible the cells are bad too. Either way, take it back.

[1] https://pushevs.com/2018/01/29/2018-nissan-leaf-battery-real-specs/
 
OP @gary , found some info in the 2012 factory service manual that may be related to your issue. i can send you a 2-page .pdf file with this info if you want it.

In the FSM there is a procedure to adjust the voltage of a new module before installation using a special tool called a "module charge balancer" for that purpose.

5FGCxuV.png


The procedure involves measuring the Max cell voltage of the pack to determine an adjustment value (AV) for the new module.
Then measure the new module voltage and discharge it below this AV.
Set the AV target value in the tool and start the adjustment.
At the end measure the voltage of the module and it should be equal to the AV target +/-10 mV.
Install the module and measure the difference between the installed module and the Max cell voltage, it should be within +/- 33 mV.

i don't have the 2018 FSM to compare, but it is likely the same sort of procedure. Unfortunately to repeat this would require opening the sealed pack cover.
 
Lothsahn said:
LeftieBiker said:
This gibes with what has been stated elsewhere: that the BMS can only manage balancing when there isn't a huge difference in cell voltages. I hadn't realized that this was one of those cases.
Click to expand...

This is the "problem" of lithium batteries. Unlike alkaline, they have almost a flat discharge curve before they fall off quickly. A small voltage difference seems like nothing at all--in reality, it can be quite a bit of capacity.

That said, you're also right. While the owner noticed a 30% reduction in range, that should have been 200mv of delta, not 60mv[1]. It's possible the cells are bad too. Either way, take it back.

[1] https://pushevs.com/2018/01/29/2018-nissan-leaf-battery-real-specs/
Click to expand...

I see balancing in my cells nearly all the time including mid range SOC's when delta top to bottom is 10 mv or less and at lower SOC (below 15%) when deltas are in the mid 150's
 
DaveinOlyWA said:
I see balancing in my cells nearly all the time including mid range SOC's when delta top to bottom is 10 mv or less and at lower SOC (below 15%) when deltas are in the mid 150's
Click to expand...

Yes, that's normal behavior. At high SOC's, small deltas in voltage indicate large capacity differences. At low SOC's, small deltas in voltage indicate small capacity differences. See the voltage curve of the Leaf cells I linked in an earlier post.

However, the user reported a 30% loss in capacity (based on range). The delta shown was 60mv at 78% SOC. Based on the voltage graph, that should be a 200mv delta for a 30% difference in capacity. That said, 60mv at 78% SOC is a large difference and the cells were either not balanced properly or defective or both.
 
Lothsahn said:
This is the "problem" of lithium batteries. Unlike alkaline, they have almost a flat discharge curve before they fall off quickly.
Click to expand...
It's LFP (LiFePO4) that has the really flat V vs SOC curve, actually two very flat regions with a small transition between them, which together cover well over half of the SOC range.

The Nissan cells do have more slope at higher SOC, in fact about 3 times (ignoring the knee at very low SOCs, which should be avoided anyway). But it's far from flat (as in horizontal) at any point. So it seems to me that SOC estimation is not terribly hard, given a decent voltage measurement.

At high SOC's, small deltas in voltage indicate large capacity differences. At low SOC's, small deltas in voltage indicate small capacity differences.
Click to expand...
Um, at high SOC, a fixed delta in voltage indicates a small change in SOC (delta y fixed, high slope, small delta x). Are you saying that this small change in SOC somehow translates to a large change in capacity? Or did you just switch around the "small" and "large" adjectives by mistake?
 
coulomb said:
Um, at high SOC, a fixed delta in voltage indicates a small change in SOC (delta y fixed, high slope, small delta x). Are you saying that this small change in SOC somehow translates to a large change in capacity? Or did you just switch around the "small" and "large" adjectives by mistake?
Click to expand...

By high, I meant 75% (as shown in the picture). The slope of the curve is rather flat there--especially compared to the bottom 10% of the battery.

And I didn't say a small change in SOC translates to a large change in capacity. I said a small change in voltage at high SOC's (50-90%) translates to a large change in capacity. SOC drops linearly as charge is drawn from the battery, as it accounts for the voltage curves of the cells in the battery.

The curve is shown here:
https://pushevs.com/2018/01/29/2018-nissan-leaf-battery-real-specs/

Between 10 and 50 Ah, the voltage changes .3V, but that covers 72% of the capacity of the battery. Between 50 and 55Ah, the voltage changes .9V, despite only covering 9% of the capacity of the battery.
 
Lothsahn said:
By high, I meant 75% (as shown in the picture). The slope of the curve is rather flat there--especially compared to the bottom 10% of the battery.
Click to expand...
Ah. The last 10% is "off the cliff", which I assume we (and Nissan) are staying away from.

Between 10 and 50 Ah, the voltage changes .3V, but that covers 72% of the capacity of the battery.
Click to expand...
Actually, I read 0.5V (2.5 divisions of 0.2V each). That's about 0.5/3.65*100% = 14% of nominal voltage. I would not call that "flat". I agree that is it flat relative to the cliff, but I assume that the cliff is off-limits. Am I wrong assuming that the cliff is off-limits?
 
coulomb said:
Lothsahn said:
By high, I meant 75% (as shown in the picture). The slope of the curve is rather flat there--especially compared to the bottom 10% of the battery.
Click to expand...
Ah. The last 10% is "off the cliff", which I assume we (and Nissan) are staying away from.

Between 10 and 50 Ah, the voltage changes .3V, but that covers 72% of the capacity of the battery.
Click to expand...
Actually, I read 0.5V (2.5 divisions of 0.2V each). That's about 0.5/3.65*100% = 14% of nominal voltage. I would not call that "flat". I agree that is it flat relative to the cliff, but I assume that the cliff is off-limits. Am I wrong assuming that the cliff is off-limits?
Click to expand...

Ah crud. I misread 3.9 as 3.7. You are right. .5V.

That said, you and I are saying the same thing with different terms. :) What I call flat, you're calling not flat. I think the primary reason is I was trying to illustrate that when at VLBW/Turtle in a Leaf, the voltage differences are huge (because you are off the cliff), whereas when it's charged, they're not. On the other hand, your experience is with other chemistries and potentially power regulators (where a .5V difference is significant). In short: Large = off cliff, Small=the normal section of the curve between cliff and 4.1V.

The assumption that Nissan is staying away from "off the cliff" is a good one, but unfortunately, not correct. To maximize range, Nissan does in fact allow cells to go quite low--here's a few posts on turtle voltage, seeing 3.2V and potentially even lower:
https://www.mynissanleaf.com/viewtopic.php?t=14143#p321871

Keep in mind that those posts are about the 24kWh Leaf, which has a different voltage curve than the one we've been looking at for the 40 kWh cells:
https://qnovo.com/wp-content/uploads/2015/07/v-charge2.gif
(you can see the cliff starts at 3.4-3.6V, depending on current draw)

This is why it's critical to immediately charge the leaf if you ever get to VLBW or Turtle--you've already started down the cliff, and it's not good to leave the cells at that low SOC for long.
 
Lothsahn said:
That said, you and I are saying the same thing with different terms. :)
Click to expand...
Ok, I think we understand and agree with each other now (other than the meaning of "flat", but flatness is a relative thing). Thanks for your patience with me.
 
On my old 30KWH battery you could indeed "drive off the cliff" going below 340 volts (about 18% charge remaining) to about 317 VDC at 3% remaining. I haven't tested the new battery to see if there were any changes.
 
I really appreciate all the advice and discussion on this issue. I took the car back to the dealership to have them take a look. They did not see any problem and did not see any problem with cell imbalance. It's not clear how they checked the balancing. The advisor explained that if there was a significant imbalance it would throw a diagnostic code, as the car did when the battery leak happened originally. So I fear that they just relied upon diagnostic codes and didn't do any more in depth measurement. I asked what could be causing the range loss if its not due to cell imbalance. No good answer, but the advisor did say the next step would be for me to report the issue to Nissan's regional support.

I'm going to drive the car until a low SOC and then do a L1 or L2 charge back up to 100%. Based on the discussion in this thread it doesn't sound like that will balance the cells much, but it will enable me to (1) Get an updated cell voltage read out from LeafSpy at different SOC levels to aid my understanding of the concepts discussed in this thread, and (2) Allow me to log the miles driven, KWh used, battery percentage and remaining range reported through a whole discharge cycle. I think this will be important data to make my case to Nissan, along with LeafSpy cell voltage read out from LeafSpy if Nissan would consider looking at that information.

Thanks again - I'll keep this thread updated.
 
The advisor explained that if there was a significant imbalance it would throw a diagnostic code, as the car did when the battery leak happened originally. So I fear that they just relied upon diagnostic codes and didn't do any more in depth measurement.
Click to expand...


This is the equivalent of saying "Your car isn't running hot - the red light doesn't come on!" Diagnostic codes are like idiot lights, just available in greater numbers. LeafSpy (especially the Pro version) is more like a gauge cluster on the dashboard.
 
gary65536 said:
I really appreciate all the advice and discussion on this issue. I took the car back to the dealership to have them take a look. They did not see any problem and did not see any problem with cell imbalance. It's not clear how they checked the balancing. The advisor explained that if there was a significant imbalance it would throw a diagnostic code, as the car did when the battery leak happened originally. So I fear that they just relied upon diagnostic codes and didn't do any more in depth measurement. I asked what could be causing the range loss if its not due to cell imbalance. No good answer, but the advisor did say the next step would be for me to report the issue to Nissan's regional support.

I'm going to drive the car until a low SOC and then do a L1 or L2 charge back up to 100%. Based on the discussion in this thread it doesn't sound like that will balance the cells much, but it will enable me to (1) Get an updated cell voltage read out from LeafSpy at different SOC levels to aid my understanding of the concepts discussed in this thread, and (2) Allow me to log the miles driven, KWh used, battery percentage and remaining range reported through a whole discharge cycle. I think this will be important data to make my case to Nissan, along with LeafSpy cell voltage read out from LeafSpy if Nissan would consider looking at that information.

Thanks again - I'll keep this thread updated.
Click to expand...

About what I expected from them. On your drive, I would make sure you have a charger near by when you get below 25% SOC. Those low cells will be quite unpredictable and may trigger Turtle. If that happens and you are not within a mile of a charger, then power down immediately and wait maybe 20 mins or so. This will equalize cells. You may have to disconnect 12 volt battery to remove Turtle alert. If you have LEAF Spy "Pro", clearing codes should do it as well.
 
How has the max-min difference progressed? Has it gotten smaller or larger after several days of driving and charging up to full? The leafspy is your best tool to track whether or not it is balancing itself back closer together.
 
gary65536 said:
I really appreciate all the advice and discussion on this issue. I took the car back to the dealership to have them take a look. They did not see any problem and did not see any problem with cell imbalance. It's not clear how they checked the balancing. The advisor explained that if there was a significant imbalance it would throw a diagnostic code, as the car did when the battery leak happened originally. So I fear that they just relied upon diagnostic codes and didn't do any more in depth measurement. I asked what could be causing the range loss if its not due to cell imbalance. No good answer, but the advisor did say the next step would be for me to report the issue to Nissan's regional support.

I'm going to drive the car until a low SOC and then do a L1 or L2 charge back up to 100%. Based on the discussion in this thread it doesn't sound like that will balance the cells much, but it will enable me to (1) Get an updated cell voltage read out from LeafSpy at different SOC levels to aid my understanding of the concepts discussed in this thread, and (2) Allow me to log the miles driven, KWh used, battery percentage and remaining range reported through a whole discharge cycle. I think this will be important data to make my case to Nissan, along with LeafSpy cell voltage read out from LeafSpy if Nissan would consider looking at that information.

Thanks again - I'll keep this thread updated.
Click to expand...

Did they do the cell imbalance check at the VLBW (---) on the dash or did they just check it at the current battery level? If not checked at VLBW, that's why it didn't throw codes. You may need to inform them on the proper procedure for how to, you know, do basic diagnostic stuff they should know.

<sarcasm>I'm SHOCKED that the dealership that didn't do the repair properly also doesn't know the procedures to detect if the repair was done wrong. </sarcasm>

I agree collecting more data is a good idea for you to do.

I will get the appropriate lines from the service manual tonight, although it'll be 2011, not your model year. Hopefully that will give you more ammunition. to deal with them.

It would also be useful to keep a video of the dash, in case your car goes to turtle prematurely. If you can show the dealership that your car goes to turtle when it shouldn't, that gives you an additional problem for the dealership to justify.
 

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