Chevy Bolt Recall

[GXMnow]

I know I am not the only person using Chevy Bolt battery modules. There have been three Chevy Bolt battery fires and they are now recalling the cars to investigate what is going on. In all 3 cases, the battery was at nearly full charge. Their short term fix is limiting the car to only charge to 90% capacity. Here is one article about what is going on.

GM Expands Major Chevy Bolt EV Recall, Adds Bolt EUV, over Battery Fire Risk

General Motors says all 2019–2022 model year Bolt EV and EUV vehicles are now being recalled because of one and, in some cases, two defects in the battery cells that could lead to fire.

www.caranddriver.com

In my system, I was charging to 57.8 volts. 58.8 volts would be a full charge of 4.2 per cell. I figured that was just over 90%. To play it safe, I backed it down to just 57 volts even. That works out to 4.071 volts per cell. Well short of the 4.2 volt full charge. In 3 months of cycling every day, no cell has even gotten warm to the touch. My currents have not been exceeding 40 amps with 2 banks in parallel. I am not at all concerned about the battery bank being a fire hazard, but I am making sure to follow any reports to see what they do find. Keeping the cell voltage a little lower is just being prudent. The charge and discharge currents that they are using in the cars is many times higher than we run using them for solar storage. If this turns out to be like the Samsung phone batteries or the Sony laptop cells, I don't think we have a worry with our use case. Those were cases where the rapid manufacture was leaving rough edges and debris inside the cells. Motion, shock, and high current cycling was cutting through the insulator and causing internal shorts. Sitting still in my garage, while charging and discharging at slow rates should not push a cell to this kind of failure mode. Sitting on or dropping a fast charged cell phone, or dropping your laptop is far more stress, let alone a DC fast charge cycle and hitting a curb in an EV. We should get a definitive answer fairly soon as they inspect the recalled vehicle packs.

I am hoping they find something stupid that is not directly related to the cells, but I will always keep a close eye on my pack. Maybe they will find the cars that caught fire had an stray bolt clamped under a battery module?? If it ever does start to get hot, I can have it unplugged and rolled out of my garage in under a minute. I did inspect my modules pretty close. The outside had no serious damage. Only one small dent in one of the aluminum plates and a bent buss bar. Nothing close to intruding on the pouch cells. But I did not separate the cells to see if anything may have been caught between cells.

This news does not make me fear these cells. But keeping the full charge voltage a little lower until they fond the real cause of the fires is just being prudent. I will always monitor them pretty close and treat them gently. I suggest anyone else using the LG Chem Chevy Bolt packs to also lower the full charge voltage to less than 90% until we know more. I found some good graphs talking specifically about NMC cells and their rather odd SOC to voltage curve. They are pretty flat from 20% up to 55% charge, only climbing from 3.51 volts to 3.67 volts. The voltage then starts to climb a bit faster. At 90%, where Chevy is telling us to stop, the voltage is up to 4.11 volts. That works out to 57.54 volts for a 14S pack like mine. I was running up to 57.8 volts. Dropping it to just 57 flat should be more than enough margin for calibration error. Based on this graph, that puts me at 85% charge. The lowest I have been running my pack is down to about 50 volts even. That is 3.57 volts per cell during discharge at 30 amps. That is right about the 40% SOC point on this graph. A bit lower than I was expecting. Most days stay above that. In the data logs from the Schneider XW-Pro, I can clearly see the curve where the voltage change slows down. I typically just dip below that. That curve appears to happen at about 55% charge.

As always, be safe.

 

[Ozark Tinkering]

I've been following the Bolt battery recall because back in Oct. of 2020 we decided to go full PHEV and we sold our 2014 Volt (very happy with that car) and took a 3 year lease on a new Bolt. That has kept us out of gas stations during the pandemic. The Bolt is a really fun little car to drive but the seats are the worst I've ever experienced. Even so I figured it would make a good place holder until '23-'24 models came out when we would have a lot more choices. The Bolt makes very efficient use of its battery and I regularly squeeze 4.3mi/kw from its battery while they base their range on 3.9mi/kw. Now with the recall that 259mile rated battery is only good for about 150miles after you discount the 70miles they want you to leave in reserve and the 50miles they want you to leave off the top. Winter is worse. I could have bought a used Leaf instead as a place holder.
What I think is a real shame is that I don't think any of the 141,000/60-66kw battery packs being replaced will be available to the DIY market to be able to do what you are doing. That's about 9 gigawatts of capacity just ground up and recycled leaving a carbon print we'll never offset.
So now I look at the Bolt in my driveway (well away from the house or shop) with a certain sadness, knowing that when they do finally notify me to come get the battery replaced, nobody will ever make use of that very gently used battery again, even though there probably isn't a thing wrong with it. It doesn't instill a lot of confidence when they tell you to park 50' away from all other cars at the grocery store. Heck they never told me to do that with me old '56 Chevy Nomad that would shoot flames out the carb when it backfired?

We don't drive much anymore so after having the Bolt for over 16 months we still have under 6,000 miles on it. I'm pretty sure that even if GM doesn't replace the battery before our 3year 36,000mile lease is done it will have had less than 12,000 miles of use. I would love to be able to take that 66kw battery off their hands and I think that with just over a dozen fires in 141,000 cars, makes chances of encountering the 2 identified flaws lining up on 1 cell pretty remote and by your description, should be easy to spot upon inspection. That's what GM wants to avoid is inspecting every cell of 141,000 battery packs already installed in cars. There simply aren't enough qualified "inspectors" out there in dealerships where the work will be performed. What they have instead are "installers" that can do a swap.

 

[GXMnow]

My brother and his wife still keep driving their two Chevy Bolts and they love them. I don't think they have their battery inspection/replacement dates yet. They set the 90% charge limit, and have not done any long trips in a while, so they get topped up at home without dropping below 8 or 100 miles remaining.

I totally agree, it will be a shame if the batteries are destroyed and not sold off to some second use site like Battery Hookup. My 36 kilowatt hours of Bolt batteries are working perfectly. According to the Schneider XW logs, I have cycled 3.6 megawatt hours in and back out of my Bolt packs in just under 1.5 years. It will be a bit higher in the next full year, since the second bank of batteries went online in the middle of last year, allowing me to cycle a bit more. I am just running them up to 85% and down to 60%. And the maximum current to the whole bank is just 60 amps. One cell could take that all day long, but I have 12 cells in parallel now. That makes my maximum discharge rate below 0.09C on 3C rated cells.