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Here are the cell voltages for my 2019 EVLT:

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They don't seem to have the pattern others are describing here. My SOC is approx 85%. Two things that may be a bit abnormal about my situation: No DCFC option, and I usually charge to 85-90% using the OEM Level 1 EVSE.

I'm editing this post the day after posting, to add more info in response to questions in subsequent posts. Added info below:

I did get the recall notice for my 2019 LT.
The door pillar sticker says car's Build Date is 5/19. Model 981FB48.
The battery sticker says "57kWh VISTA2.0 Cell Module Assembly B2.0.0" LiMM-C.F.
I don't see an obvious date of manufacture on the battery sticker.
There is a yellow and a green dot on the battery sticker.

Another "odd" point is that I'm not using TorquePro to extract the battery info, as most people seem to do. I recently installed the app "Car Scanner ELM" on my IPhone, and used it to extract all data for about 60-seconds, while the car was sitting in my driveway in Alabama after being charged to 85% several days earlier on the OEM L1 charger. I got 8 samples of each cell voltage during the recording session, which I then averaged for each cell to get the values shown in my graph.

When I imported the CSV file exported by the CarScanner app into Excel, I found that the columns containing the battery voltage data had been imported/sorted in alphabetical order rather than numerical order, i.e. the data headings are "BatteryCellVoltage #1", "BatteryCellVoltage #2", etc. But the columns were ordered 1, 11, 12, 13, ... 2, 20, 21, 22, etc. So I had to do some "post-processing" to extract the number field from each heading and convert the # field to a numeric value, then sort the columns by numeric value to make the graph. In the end I believe I got it correct, and I did check against the original CSV file to verify that the "low" voltage values are as shown in the bar graph. I think I got it right, but there's always a chance I got it wrong. Or maybe a bug in the way the app extracts the voltages?
 

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Yes, because you don't use float voltage on lithium, I was trying to use a common term to explain applying a continued current to lithium batteries after they've reached their peak voltage. The concern is, if the BMS is trying to balance cells, is it allowing certain cells to continue receiving power even after they've reached their peak voltage.
The last portion of the charge cycle is at a constant voltage. The charger voltage is held constant and the current gradually decreases to a minimum value as the cell stabilizes at that voltage. If a cell is low, the voltage on the other cells will tend rise a bit higher and be clamped by the BMS. This will allow the low cell to be charged a bit more by allowing it to go higher.

The BMS is designed only to handle a small amount of power to balance out small differences. If something goes awry and this power gets too high, certainly the BMS could overheat. This could potentially start a fire in the battery pack.

Now, Professor Kelly mentioned that the BMS is the same part number that was used in the Volt. This is good since it is a proven entity but the Volt pack is much lower capacity. Could this allow the BMS to overheat in the Bolt due to some "corner condition" that can occur? Major conjecture here! Of course this might be fixed with a software patch.

This whole system was undoubtedly studied very thoroughly during the design so what ever is going on would seem like some very odd corner case.
 

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Discussion Starter #103
Here are the cell voltages for my 2019 EVLT:

View attachment 31722

They don't seem to have the pattern others are describing here. My SOC is approx 85%. Two things that may be a bit abnormal about my situation: No DCFC option, and I usually charge to 85-90% using the OEM Level 1 EVSE.
Interesting. Roughly the same spread as earlier packs but not the same pattern.
 

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Here are the cell voltages for my 2019 EVLT:

31722
That's interesting, especially because it seems as though you have a Korean made pack, even with your late build date. Did you take a pic of your battery sticker?
 

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In these cases, you also have to account for a number of performance factors, including linguistic barriers, training, workplace culture, etc. Production line employees don't always do exactly what they're told, and if they find that plugging 1, 3, 5, 7 is faster than plugging 1, 2, 3, 4, they might do the former, especially if they aren't aware of the ramifications.

Keep in mind, it looks like Hyundai was subject to some of the same LG QC issues after GM had already corrected those issues with their own LG partnership.

*Edit: And frankly (I'm sure I'm not the only one here who feels this way), I do find your post disrespectful. Anyone who's followed Professor Kelly's channel knows how assiduous, meticulous, and knowledgeable he is. To assume that assembly line employees have the same knowledge, skills, and attitudes as an industry expert, master mechanic with decades of hands on experience is a bit insulting.
OK, wow. You either read into or misread my comment about Kelly. It was in no way disrespectful and if anything was complementing him for his knowing the fine details. He did it all, so it seems by reading the factory manual. You are telling me that Koreans on the assembly line don't understand Korean? Do you know anything about quality control or QC? I am to believe by you that no one is looking over the shoulders of these production line workers and possibly 68,000 Bolts were produced by plugging in wires 1,3,5,7 instead of 1,2,3,4. I have had many products where inspectors initials or some mark was indicated. Sorry, your story doesn't fly. I think you are so invested in being correct you can't see the forest through the trees. I said "I find it hard to believe Weber caught on to this easily in making his video but the largest EV maker....." How you see this as disrespect when in fact it was a complement and appreciation is hard to fathom.
 

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Here are the cell voltages for my 2019 EVLT:
Interesting indeed. I think this is the first we have seen that doesn't have the low and high cells clumped together in the same spots. It's crazy how we all have a .02V spread though, regardless of which cells we are talking about. That leads me to believe that the cell balancing has a cutoff of .02V, meaning that during balancing, whenever it gets all cells within .02V variance, it stops trying to balance. The thing that intrigued me before is why almost all of us see the same high/low cells... but this latest one looks pretty random instead. I might try charging mine next time with the 120V charger to see if it makes any difference. I don't see how it could, but might as well see.

Mike
 

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Respectfully, I find it hard to believe that Weber caught on to this easily in making his video but the largest manufacturer of EV batteries in the world with a revenue of 21 billion dollars could not instruct the assembly plant to hook up the wires in the correct order. So are you saying it is every car or just a few? All they need to do is drop the batteries and re-arrange a few wires? Sorry, does not compute on my end. There are defective cells, plain and simple. Maybe the BMS is defective in that it can't safely dissipate heat for the period of time it needs to just gets a short in it and catches on fire. I am incredulous to believe the BMS does not have an abort function. If it does not then we may as well call it Willy Wonka's Chocolate Factory.
Professor Kelly read this installation procedure from the Chevy service manual. He did not discover this or make it up. The procedure is the same as the Volt.

The ramifications of making an error here are unknown to us. About all we might take away is that possibly the BCM is defective in some way if the procedure was not followed. How this might relate to the operation of the car is unknown. Hopefully any damage results in a fault during testing of the system.
 

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Interesting indeed. I think this is the first we have seen that doesn't have the low and high cells clumped together in the same spots. It's crazy how we all have a .02V spread though, regardless of which cells we are talking about. That leads me to believe that the cell balancing has a cutoff of .02V, meaning that during balancing, whenever it gets all cells within .02V variance, it stops trying to balance. The thing that intrigued me before is why almost all of us see the same high/low cells... but this latest one looks pretty random instead. I might try charging mine next time with the 120V charger to see if it makes any difference. I don't see how it could, but might as well see.

Mike
My early 2019 does not show that grouping characteristic but I mostly use 120V charging and I almost never charge to 100%. My car is subject to the recall.

I'll have to log the voltages more carefully since so far I have just been looking at them manually. I have been rather amazed at how close the voltage balance is even at random states of charge.
 

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OK, wow. You either read into or misread my comment about Kelly. It was in no way disrespectful and if anything was complementing him for his knowing the fine details. He did it all, so it seems by reading the factory manual. You are telling me that Koreans on the assembly line don't understand Korean? Do you know anything about quality control or QC? I am to believe by you that no one is looking over the shoulders of these production line workers and possibly 68,000 Bolts were produced by plugging in wires 1,3,5,7 instead of 1,2,3,4. I have had many products where inspectors initials or some mark was indicated. Sorry, your story doesn't fly. I think you are so invested in being correct you can't see the forest through the trees. I said "I find it hard to believe Weber caught on to this easily in making his video but the largest EV maker....." How you see this as disrespect when in fact it was a complement and appreciation is hard to fathom.
I might know a bit more about QC than you seem to think, especially when it comes to gap analyses and performance management. Assuming that factory workers will follow procedures to a T (i.e., doing what is correct over doing what is easy) is a big stretch, and assuming that QC can actually catch the types of issues that aren't necessarily apparent or possibly even tracked is an even bigger stretch. This is especially the case of a company and facilities that have already proven to be lacking in the QC department. Ultimately, what is measured gets done. If these type of procedural operations weren't tracked, there'd be no reason for them to trigger any sort of finding.

Now sure, we don't know that what Professor Kelly noted about the order is what happened, but the consequences of incorrect connection order do align with what we've seen. To me, regardless of the cause, the voltage spreads we're seeing from these early Bolt EVs are clearly unacceptable; otherwise, why would GM make it a point to correct them. And if not a QC issue, why would GM note that their Michigan-built EVs weren't subject to the same recall, despite using identical or interchangeable components?

As for being invested in being correct, not at all. However, I will push back on people using "Black Hat" thinking that seeks to dismiss other people's theories without any evidence or proof of their own.
 

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We are all just speculating at this point but prof. Kelly's quote was that connecting cables in the wrong order could cause "internal damage" to the BMS. So in my mind, it is entirely possible that if things were connected in the wrong order, the system (BMS) might pass initial inspection but the damage is done: it may cause the BMS to partially fail later down the road which could potentially cause a lot more than the .02V variance most of us see. Possible? I think so. Likely? No way for us mortals to know.

Mike
 

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Here are the cell voltages for my 2019 EVLT:

View attachment 31722

They don't seem to have the pattern others are describing here. My SOC is approx 85%. Two things that may be a bit abnormal about my situation: No DCFC option, and I usually charge to 85-90% using the OEM Level 1 EVSE.
First pack we’ve seen on this thread that has different clusters of awry cells, as others have pointed out. Was your Bolt subject to the recall? Interesting points as well on the L1 charging. Will look into that as well.
 

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First pack we’ve seen on this thread that has different clusters of awry cells, as others have pointed out. Was your Bolt subject to the recall? Interesting points as well on the L1 charging. Will look into that as well.
Also interesting is the fact that this one that is different still has about the same number of cells that are notably lower than the average and about a half dozen that are higher: they just aren't in "clumps" like most of the other batteries. But they are similar in that about a half dozen cells show about .01V lower than the average and about a half dozen show .01V higher than the average (or median if you like).

Mike
 

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Also interesting is the fact that this one that is different still has about the same number of cells that are notably lower than the average and about a half dozen that are higher: they just aren't in "clumps" like most of the other batteries. But they are similar in that about a half dozen cells show about .01V lower than the average and about a half dozen show .01V higher than the average (or median if you like).

Mike
Yep. Makes me wonder whether Eric’s theory on how the packs were assembled has more to it, actually.
 

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Yep. Makes me wonder whether Eric’s theory on how the packs were assembled has more to it, actually.
Yeah, just a theory. The alternative is, though, that LG's quality control at that point was just so poor that cells coming off the same assembly line couldn't be balanced. I don't see how that's plausible, though, as that would likely require an issue with the chemistry itself. Given that GM can add newer modules to older packs and still align their voltages makes me think that's not right.

Maybe another interesting bit of data to gather... Do we have voltage spreads for Bolt EV owners whose batteries were replaced under recall? Both the entire battery and/or individual modules (for the second round).
 

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I will add a bit more data about my "outlier" battery. I will go back and edit my original post to add this info as well.

I did get the recall notice for my 2019 LT.
The door pillar sticker says car's Build Date is 5/19. Model 981FB48.
The battery sticker says "57kWh VISTA2.0 Cell Module Assembly B2.0.0" LiMM-C.F.
I don't see an obvious date of manufacture on the battery sticker.
There is a yellow and a green dot on the battery sticker.

Another "odd" point is that I'm not using TorquePro to extract the battery info, as most people seem to do. I recently installed the app "Car Scanner ELM" on my IPhone, and used it to extract all data for about 60-seconds, while the car was sitting in my driveway in Alabama after being charged to 85% several days earlier on the OEM L1 charger. I got 8 samples of each cell voltage during the recording session, which I then averaged for each cell to get the values shown in my graph.

When I imported the CSV file exported by the CarScanner app into Excel, I found that the columns containing the battery voltage data had been imported/sorted in alphabetical order rather than numerical order, i.e. the data headings are "BatteryCellVoltage #1", "BatteryCellVoltage #2", etc. But the columns were ordered 1, 11, 12, 13, ... 2, 20, 21, 22, etc. So I had to do some "post-processing" to extract the number field from each heading and convert the # field to a numeric value, then sort the columns by numeric value to make the graph. In the end I believe I got it correct, and I did check against the original CSV file to verify that the "low" voltage values are as shown in the bar graph. I think I got it right, but there's always a chance I got it wrong. Or maybe a bug in the way the app extracts the voltages?
 

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I will add a bit more data about my "outlier" battery. I will go back and edit my original post to add this info as well.

I did get the recall notice for my 2019 LT.
The door pillar sticker says car's Build Date is 5/19. Model 981FB48.
The battery sticker says "57kWh VISTA2.0 Cell Module Assembly B2.0.0" LiMM-C.F.
I don't see an obvious date of manufacture on the battery sticker.
There is a yellow and a green dot on the battery sticker.

Another "odd" point is that I'm not using TorquePro to extract the battery info, as most people seem to do. I recently installed the app "Car Scanner ELM" on my IPhone, and used it to extract all data for about 60-seconds, while the car was sitting in my driveway in Alabama after being charged to 85% several days earlier on the OEM L1 charger. I got 8 samples of each cell voltage during the recording session, which I then averaged for each cell to get the values shown in my graph.

When I imported the CSV file exported by the CarScanner app into Excel, I found that the columns containing the battery voltage data had been imported/sorted in alphabetical order rather than numerical order, i.e. the data headings are "BatteryCellVoltage #1", "BatteryCellVoltage #2", etc. But the columns were ordered 1, 11, 12, 13, ... 2, 20, 21, 22, etc. So I had to do some "post-processing" to extract the number field from each heading and convert the # field to a numeric value, then sort the columns by numeric value to make the graph. In the end I believe I got it correct, and I did check against the original CSV file to verify that the "low" voltage values are as shown in the bar graph. I think I got it right, but there's always a chance I got it wrong. Or maybe a bug in the way the app extracts the voltages?
Ahhh okay so this might explain the variance if you’re using a different tool. You may be right in terms of how the app extracts or handles the data.
 

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It just hit me after reading the above. We are all assuming Torque Pro is exactly right. What if, all along, this is nothing but a bug in Torque Pro? Having done some OBDII programming in the past, I know all these voltages are sent in digital form. For example, the voltage may be a 16 bit value in the range 0-65535 and then you have to take that value and convert it to floating point (using whatever data format they are using) to get the actual voltage. It's kinda "funny" that the two clumps in question start at around cell 8 and cell 64 which happen to be boundaries between 3-4 bits and 6-7 bits when encoding the cell number. I'm not saying that has any bearing (I doubt it) but it does get me wondering.

Let's just take one possible example. Perhaps due to the design of the BECM or the wiring, GM knew that there could be a small voltage offset in some cells in some regions (meaning the raw voltage reading my be off a little - high or low from the ACTUAL voltage). In order to get the most accurate readings possible, there might be a "raw" voltage reading and some sort of "calibration" that amounts to an offset that should be applied to that reading to get the most accurate voltage. This could work on a cell-by-cell basis: some sort of calibration is performed/stored (by more accurate diagnostic equipment when the battery is being manufactured), and the offsets store things like cell one has a .00134V offset, Cell 2 has a -.00166V offset (again based on the raw BECM reading), and so on down the line. If Torque Pro reads the raw voltage and doesn't apply the stored offsets, it could cause the problem we are seeing... while at the same time if the BECM does apply those corrections by cell, it would know the actual voltage which MAY be better than we think by looking at the Torque Pro figures.

Speculating even further down the line (I'm really grabbing at straws here), if something like that is the case, maybe that calibration is what was done wrong at the Korean plant.

Just something to ponder. I don't think we can assume Torque Pro is perfect any more than we can assume the BECM is perfect.

Mike
 

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Let's just take one possible example. Perhaps due to the design of the BECM or the wiring, GM knew that there could be a small voltage offset in some cells in some regions (meaning the raw voltage reading my be off a little - high or low from the ACTUAL voltage). In order to get the most accurate readings possible, there might be a "raw" voltage reading and some sort of "calibration" that amounts to an offset that should be applied to that reading to get the most accurate voltage.
I don't think that's too far fetched. We're dealing with very small voltages, there might be adjustments based on the monitoring wire's length back to the BMS. Longer wire = more resistance = adjustment possibly needed. I don't remember the pack layout good enough, so this may not be a reasonable guess. And I can't remember how the wiring was run when I watched Dr. Kelly's videos.
 

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I don't think that's too far fetched. We're dealing with very small voltages, there might be adjustments based on the monitoring wire's length back to the BMS. Longer wire = more resistance = adjustment possibly needed. I don't remember the pack layout good enough, so this may not be a reasonable guess. And I can't remember how the wiring was run when I watched Dr. Kelly's videos.
Yeah, I thought about that. I kinda shot that down in my head a bit because the affected groups of cells we are talking about are only some of the cells in 2 particular modules (not all cells in the module are affected). The cables/connectors looked like they ran per module so you'd expect an adjustment per module based on wire length, but it shouldn't affect individual cells within the module. Or at least not appreciably (you'd think). IF there is an adjustment/offset, it might have more to do with tolerance of the individual A/D converters. Then again, maybe I'm off base too. I also noticed that the "edge cells" in each module are repeated as far as the wiring: like 1-10 on one cable and the next has 10-19, and so on. Prof. Kelly said you need to do that as a reference, else voltage from module to module would be off. If you discount the edge cells, that leaves 8 cells in the middle (of all but the two back modules) and... we have about 8 cells high and 8 cells low in most people's graphs. Hmm.

I "think" too much (if you can call it that). :D

Mike
 

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Generally the BMS chip can measure and load each individual cell. There need not be any particular correspondence between the connectors or cells and the BMS logic. The BMS chip used in the Volt and likely the Bolt is apparently proprietary to LG so we really don't know much about the details. The photos do look like a fairly standard BMS design.

I did review some comments I found about the Volt and apparently each cell can be loaded by approximately 100ma (0.1A) by the BMS. The BMS logic sequences through all of the cells and slightly discharges the highest ones to obtain a better balance. It likely only loads a few of them at any one time.

So basically what you see are the 100ma loads sequencing on and off to achieve a better balance. The specific algorithm is much studied in an effort to arrive at optimal cell utilization.

This causes me to suspect that the groupings of high and low cells is simply some artifact of the cell balancing algorithm. This type of balancing could occur at any state of charge.

I would expect a faulty cell to regularly be at a much lower voltage than the rest. The most serious cell failure is shorting. This can be slowly progressive so it might be detected by careful monitoring. On the other hand, not having this happen is a primary goal of the cell design. It should be an almost non existent occurrence.

This is all fun to think about but who knows. Sabotage anyone? lol
 
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