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Discussion Starter #1
With all of the recent hubbub about the battery investigation, and us suspecting it could be due to increased resistance in failing cells, it could be interesting for those who have TorquePro to post their cell voltages and voltage spread.

This could give us an idea of at least trends in the voltage variation / spread vs. manufacturing year, location, chemistry, etc.

2017 Bolt (~20,000 mi):
  • SoC raw: 89.8%
  • Max (cell 9): 4.082 V
  • Min (cell 66): 4.060 V
  • Spread: 0.02213 V
  • Average: 4.071 V
  • Standard deviation: 0.003425 V
31639



2020 Bolt (~2,000 mi):
  • SoC raw: 63.1%
  • Max (cell 29): 3.783 V
  • Min (cell 65): 3.777 V
  • Spread: 0.005747 V
  • Average: 3.781 V
  • Standard deviation: 0.001148 V
31644


Some notes on my methods:
  • Car was parked after a ~15 minute drive to work. Since it takes some time for TorquePro to read all the values, what I'm showing is average values for each cell over several (~10 or so) timepoints.

Any other suggestions for data to log / calculate?
 

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With all of the recent hubbub about the battery investigation, and us suspecting it could be due to increased resistance in failing cells, it could be interesting for those who have TorquePro to post their cell voltages and voltage spread.
If I knew enough about IT to log and post this stuff, I probably wouldn't have retired. :unsure: But from just looking at the cell voltages, as I have them arranged in numerical order, our 12/16 build looks very similar to yours. Highest and lowest cells in the same groups, and to similar extent. Although, my spread has always been about 0.025 volts, so a bit worst than yours, at least in that snapshot.
 

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Discussion Starter #4
Before and after charging on 11/14, according to Juice Net 10.89 Kwh
Your pattern looks similar to my 2017, where the module containing cells 9 - 16 is the highest and the module containing 65 - 72 is the lowest. What year is your Bolt?
 

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How are you getting these nice graphs. I have Torque Pro and I've added displays for all 96 cells. I looked yesterday at about 56% charge and they were all in the 3.70 to 3.72 range. Is there a way to get these graphs from Torque Pro?

Mike
 

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I'll ask a Great Question™

What's the best workflow for logging this data to a spreadsheet or whatever? And by workflow, I mean, which software packages and what steps, flow chart style, do we execute (not a click by click)

Are there any better packages than Torque to do this?
 

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Your pattern looks similar to my 2017, where the module containing cells 9 - 16 is the highest and the module containing 65 - 72 is the lowest. What year is your Bolt?
Two years ago, when we got Torque Pro, I noticed this pattern. I got all excited, thinking it was module related. I went back through Professor Kelly's video to find which cells are in which modules. There are ten modules, permanently attached into five sections. Eight modules have ten "cells" each, and two have eight "cells" each. Sadly, none of these patterns is totally contained within single modules, or single sections This tells me the problem is in the pouch cells themselves, or in the process of spot welding three of them into a "cell."

Module #1, Section #1, cells 1-10
Module #2, Section #2, cells 11-20
Module #3, Section #3, cells 21-30
Module #4, Section #4, cells 31-40
Module #5, Section #5, cells 41-48
Module #6, Section #5, cells 49-58
Module #7, Section #4, cells 59-66
Module #8, Section #3, cells 67-76
Module #9, Section #2, cells 77-86
Module #10 Section #1, cells 87-96
 

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I've been envisioning the scenario in my head and I don't know if this is right or I'm totally off base but... LG makes the cells regardless of whether the pack was manufactured in Korea or Michigan so my suspicion from the beginning has been that either: (a) the cells were manufactured in Korea and the pack assembled there too - the recalls, or (b) the cells are still manufactured in Korea and then shipped to Michigan where they are put into the packs and the pack assembled - no recall yet. If this is the case, then there should be no difference in the actual cells and it would point to a problem in the manufacture of the pack: as you say, potentially some spot welding joint(s), maybe how the BMS wiring is connected inside, or something else in the way the cells are actually put into the pack and connected/secured.

Mike
 

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Further... my mind keeps wandering back to the Prof. Kelly video where he was showing the BMS and he stated in no uncertain terms that you must get the connectors right and not connect/disconnect them in the wrong order because if you don't have a good connection at the BMS connectors, the BMS will keep trying to balance something that is impossible to balance and it could cause the BMS to overheat and have "internal damage". Maybe even a fire (not his words - my own extrapolation of his words). Given how he stressed this, I can imagine bad spot welds, wiring routes, or something similar causing the BMS to "lose its mind" trying to balance cells and either overheat itself, or overheat some cells in the process. Perhaps this is the manufacturing defect, and why it only seems to happen on fully charged cars (where balancing is done)?

Mike
 

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Discussion Starter #11
How are you getting these nice graphs. I have Torque Pro and I've added displays for all 96 cells. I looked yesterday at about 56% charge and they were all in the 3.70 to 3.72 range. Is there a way to get these graphs from Torque Pro?

Mike
I had TorquePro export the data that it's displaying to a log file, which is a .csv file that I opened with excel, then averaged the voltages for each cell and created a graph.

Two years ago, when we got Torque Pro, I noticed this pattern. I got all excited, thinking it was module related. I went back through Professor Kelly's video to find which cells are in which modules. There are ten modules, permanently attached into five sections. Eight modules have ten "cells" each, and two have eight "cells" each. Sadly, none of these patterns is totally contained within single modules, or single sections This tells me the problem is in the pouch cells themselves, or in the process of spot welding three of them into a "cell."

Module #1, Section #1, cells 1-10
Module #2, Section #2, cells 11-20
Module #3, Section #3, cells 21-30
Module #4, Section #4, cells 31-40
Module #5, Section #5, cells 41-48
Module #6, Section #5, cells 49-58
Module #7, Section #4, cells 59-66
Module #8, Section #3, cells 67-76
Module #9, Section #2, cells 77-86
Module #10 Section #1, cells 87-96
Thanks! I wasn't sure what cells were in what modules, but I knew that you would have that info!
 

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I had TorquePro export the data that it's displaying to a log file, which is a .csv file that I opened with excel, then averaged the voltages for each cell and created a graph.
I have tried going into the settings on the Torque Pro screen, and selected start logging, and stop logging. When I send this file to email, it is all about speed, distance, location...nothing about PID data. Where do I go to select PID data?
 

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The battery consists of 96 "cells" in series. But each "cell" has multiple "pouches" in parallel. Do I remember it correctly?

-TL

PS. Found it on Wikipedia. 96 "cell groups", generally called cells. 288 "cells", or pouches. So 3 pouches in parallel in each cell.

It is interesting to see max and min cell voltages seem to happen in same modules across different cars. They don't seem random, do they?

Putting cells in parallel is tricky business. Hard to control currents through each cell.
 

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Discussion Starter #14 (Edited)
I have tried going into the settings on the Torque Pro screen, and selected start logging, and stop logging. When I send this file to email, it is all about speed, distance, location...nothing about PID data. Where do I go to select PID data?
I'm definitely not an expert in Torque Pro, but here's the options I have selected. BTW I don't have email logging, I just grab the log file directly from my Android device and transfer it to my PC.
  • Synchronous logging
  • Log when Torque is started
  • Rotate logfiles
  • Discard trips < 0.5 mi
Now that I think of it, I kind of remember an issue I had where it wouldn't log any data values that I wasn't showing on the display screens. So I was constantly going back and forth between the displays until all the cell values refreshed multiple times. Perhaps there's an easier way, but that's the way I got it to work and I haven't spent the time looking for a more efficient way.
 

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With all of the recent hubbub about the battery investigation, and us suspecting it could be due to increased resistance in failing cells, it could be interesting for those who have TorquePro to post their cell voltages and voltage spread.

<snip>

Any other suggestions for data to log / calculate?
I would love to participate in this effort, but am not yet equipped.
Does something like a cookbook for getting started with OBD2 and TorquePro on a Bolt EV exist anywhere on this site?
The OBD2 adapter and TorquePro software are easily tracked down. Are there plug-ins that users would recommend, or can TorquePro handle all the relevant data collection/logging?
Someone in another post asked about PID's. Are these documented on this site?

[The OBD2 & TorqePro tools would be usable with the sail boat I'm converting from diesel to electric auxiliary propulsion, so I'd have two applications for them!]
[-tv]
 

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I would love to participate in this effort, but am not yet equipped.
 

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I've been envisioning the scenario in my head and I don't know if this is right or I'm totally off base but... LG makes the cells regardless of whether the pack was manufactured in Korea or Michigan so my suspicion from the beginning has been that either: (a) the cells were manufactured in Korea and the pack assembled there too - the recalls, or (b) the cells are still manufactured in Korea and then shipped to Michigan where they are put into the packs and the pack assembled - no recall yet. If this is the case, then there should be no difference in the actual cells and it would point to a problem in the manufacture of the pack: as you say, potentially some spot welding joint(s), maybe how the BMS wiring is connected inside, or something else in the way the cells are actually put into the pack and connected/secured.

Mike
Further... my mind keeps wandering back to the Prof. Kelly video where he was showing the BMS and he stated in no uncertain terms that you must get the connectors right and not connect/disconnect them in the wrong order because if you don't have a good connection at the BMS connectors, the BMS will keep trying to balance something that is impossible to balance and it could cause the BMS to overheat and have "internal damage". Maybe even a fire (not his words - my own extrapolation of his words). Given how he stressed this, I can imagine bad spot welds, wiring routes, or something similar causing the BMS to "lose its mind" trying to balance cells and either overheat itself, or overheat some cells in the process. Perhaps this is the manufacturing defect, and why it only seems to happen on fully charged cars (where balancing is done)?

Mike
Yes, this is along the same lines that I was thinking. It might be something about the pack construction process. The BMS sequencing is a good call. The other thing that keeps coming to my mind is initial top balancing of the cells.

Something to keep in mind in all this is that, while LG is a battery cell manufacturer, they are not necessarily a battery pack developer. The Bolt EV was one of LG's first, off the shelf battery packs, and this might be an illustration that their processes aren't all in order.
 

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Yes, this is along the same lines that I was thinking. It might be something about the pack construction process. The BMS sequencing is a good call. The other thing that keeps coming to my mind is initial top balancing of the cells.

Something to keep in mind in all this is that, while LG is a battery cell manufacturer, they are not necessarily a battery pack developer. The Bolt EV was one of LG's first, off the shelf battery packs, and this might be an illustration that their processes aren't all in order.
I am just an amateur and neophyte in this topic, so, it's with respect that I ask, Mikey & News, how is it that the kind of basic BMS design flaw you're discussing as a possible cause or contributor would not lead to many more failures than has been the case? BMS design has benefited from decades of development and is pretty well understood by the industry. Even those designed for amateur use (such as those from Orion and Dilithium Design) have safety features built in (utilizing constant voltage & temperature monitoring as well as balancing functions) that would manage the type of issue you're discussing.
Wouldn't it make more sense to presume that individual manufacturing defects are the root of the battery failures, and possibly fires (they don't necessarily have the same causes!), and that the failure is occurring at the cell level? Assuming that there are three cells in parallel in 96 groups [96S3P], and that monitoring and balancing is done at the group level, it might be possible for a single cell failure to result in reduced capacity of the entire pack without resulting in a fire if the cell failure was of a benign nature, such as, as News speculates, a spot weld failure. But if the failure was an internal cell short it could result in a runaway and fire in multiple cells.
Either of these scenarios seems a more plausible explanation for a failures with a relatively low incident rate that would likely result from a basic design flaw in the BMS.
The article I'd cited elsewhere on this discussion board appearing in InsideEVs would suggest a root cause that's pretty subtle: My Chevy Bolt Is On Third Battery Pack: Here's Why
Interestingly, I've read that Tesla (which uses cylindrical cells, or course, rather than the pouch cells used by several of the OEMs) is considering making a change in its China-manufactured cares to Lithium Iron Phosphate [LiFePO4] chemistry, mainly due to better availability in that country, but also due to advances made that enable that much safer chemistry to support the high rates of charging and draw required by consumer vehicles.
If consumers are reluctant to buy electric vehicles due to concerns about fires, then the OEMs will ultimately have to adopt safer chemistry and more refined manufacturing processes.
[-tv]
 
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