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Discussion Starter #1
I had an interesting experience with by 2012 Volt this morning. Seems like it overcharged the battery by quite a bit.


OnStar had sent me a charge complete email at 7:28AM. I went to my garage at about 7:30AM and noticed the TMS fan/circulator were running and drawing power from the EVSE (heard the relays click when I unplugged). That's not too unusual in this hot weather right after a charge completes (80F in my garage this morning).


When I started the car and pulled out I noticed regen wasn't working (thought I had the car in D instead of L). I then looked at the guess-o-meter and it said 50 Miles, which I think is the max it will show in a Gen1. Mine normally says 43-48 miles. Regen kicked-in after about 6 miles driving, and the first battery bar lasted for 11 miles before it disappeared. After that the battery seemed to deplete at my normal rate, about 5 miles per bar.


My guess is that several of the cell/subpack units in the battery were overcharged and the BMS didn't have time to balance them since I left very shortly after the charge completed. But, I very commonly do that and this is the first time I've seen this. It's nice to get the extra range, but I'm a bit concerned that I'm going to have issues with the battery if this keeps happening. The car has 85000 miles on it, about 75% electric. Since it's early Gen1, the battery warranty ends at 100,000 miles.


Anyone ever have this happen?


Thanks!
 

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I am not familiar with that particular condition, but my feeling is that is just another example of the sophisticated ways the car has of protecting itself. As you suggested, you probably just interrupted a normal process and the car had to compensate.

Also remember that the battery is never fully charged, so being "overcharged" just means that it is a little less undercharged that one time. That will not damage the battery.
 

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I've had my 2012 for nearly 4 years now. I live at the top of a decent hill. If I am in L and I leave my foot off of the pedal completely the car maintains 25 mph down the hill. I usually precondition my car twice before leaving in the mornings. I have experienced the condition you described once in my daily commute. I left one morning in L and took my foot off of the pedal to go down the hill. I noticed that I quickly gained speed as if I was in D. It was quite surprising because it was so out of the norm and it is something that I do every day. That being said, I've only had it happen once, and I've been on the lookout for it since then. I'd be curious to know if you see it more often.
 

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I then looked at the guess-o-meter and it said 50 Miles, which I think is the max it will show in a Gen1. Mine normally says 43-48 miles. Regen kicked-in after about 6 miles driving, and the first battery bar lasted for 11 miles before it disappeared. After that the battery seemed to deplete at my normal rate, about 5 miles per bar.
I can't speak to the topic of over-charging but, 50 is not the max value on a GEN I. With conservative driving techniques, my wife and I often start with 50-55 on the meter in Spring and Fall down here - ~70* temps. Descending down Pikes Peak in 2013 from a reading of 3 produced a reading of 56 by the time we reached the Interstate in Colorado Springs.

Often, if we interrupt the charging at a particular phase, we'll travel 5-6 miles before the estimate changes at all, then back to a normal countdown. We chalk it up as normal recalculations.
 

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The condition you describe can indeed be a bit disconcerting. I never had it happen with any of my Volts, but the first time I charged my Model X to 100% (for a long trip that had no supercharging available), I was caught off guard by the lack of deceleration that regen provides. The Tesla has even more aggressive regen, so you hold off taking your foot off the pedal that much longer- with that much less reaction time available. I believe that car manufacturers should provide a warning: 'Regeneration Limited due to battery capacity. Prepare to brake earlier.' Think about it; for all intents and purposes, you experience something akin to a brake failure. Definitely not good from an end user standpoint.
 

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Seems normal to me that a full battery (as determined by GM battery rules) is not interested in regen juice. If you could use regen juice right away, you could shorten your charge time by 15 minutes....
 

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I can't speak to the topic of over-charging but, 50 is not the max value on a GEN I. With conservative driving techniques, my wife and I often start with 50-55 on the meter in Spring and Fall down here - ~70* temps.
50 is the max value for EV range shown on 2011-2012 Volts. I think 2013's increased to 60 with the added pack capacity, although I thought that was only in 2014. Admittedly, I've never seen over 50 on my 2013, but it looks like you have a 2013 and have seen it.
 

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Discussion Starter #9
50 is the max value for EV range shown on 2011-2012 Volts. I think 2013's increased to 60 with the added pack capacity, although I thought that was only in 2014. Admittedly, I've never seen over 50 on my 2013, but it looks like you have a 2013 and have seen it.


That makes sense. The guess-o-meter stayed at 50 miles for 5-6 miles (around when regen started working). That's why I assumed it was the max reading the meter would show.


Based on my normal summer drain rate of 5-5.5miles/kwh, one bar normally representing about 1kwh in early Gen1s, and my first bar taking about 11 miles to disappear this morning, it seems like the battery was overcharged by about 1kwh. That's not too bad, unless it was all concentrated in a small number of very overcharged cells.


I would guess that post-charge cell balancing would normally take care of this issue, but it's still not good to have wasted 1kwh of extra charging that the cell packs would then dissipate as heat during cell balancing. That's assuming my memory is correct and that the BMS does discharge overcharged cell-packs with a small resistive element.


I'll keep an eye out for any more issues and bring it to the dealer if need be. I assume they can pull some advanced logging on the individual cell pack charging to see if one or more of them have a problem.
 

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I too live at the top of a big hill, and after burping my 2012 Volt, I had it stop doing regen before the making it to the bottom of the hill. I figured I had maxed out the buffer, so I gave up on burping the battery. I rather be safe and not possibly stress the battery. I usually don't use the full charge around town anyway.
 

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Discussion Starter #12
Normal behaviors all

WOT

PS> You CANNOT overcharge a Volt

Thanks for chiming in WOT. I've been reading this forum for enough years to respect your input. Hopefully this was just a one-off. If it does keep this up, I hope it throws a code so I don't have the dealer looking at me like I'm crazy when I bring it in for having too much range!
 

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Hey CCIE, did you get more actual EV range from that charge? I've had this happen in my '13 a few times (in two directions--sometimes it thinks it "under-charged" and goes into PPR, but only if I interrupt the charge cycle--this will last a minute or two and then return to normal). Likewise, a couple times it appeared to "overcharge" (60 miles max on a '13) but in a few minutes it gradually returned to the expected range, and I didn't get any more than the typical EV miles out of that charge.

I've had both issues investigated--no codes. Likely an occasional "bug" in the system reading/estimating the actual SOC--a situation that quickly corrects itself after a few minutes given the advanced programming.

I would still get it checked out if it happens again.
 

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I do this often and on purpose, sometimes called
"Burping "
A volt , i get a couple hundred watt hours extra when I time it right.

Never noticed disabled regen
 
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