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Discussion Starter #1
Searched for a thread and didn't find this so here goes... I've had my 2019 for almost 3 months and when I first got it, I set my max charge level (equivalent to hilltop reserve in older models but you can set the percentage) to 80%. I typically drive 30 miles round trip but sometimes go as far as 120 round trip so I figured I'd leave it at 80% max charge to cover any situation. Until Friday, I had only taken 30 mile trips and plugged it back in: in those instances it had always charged to 83%. I wondered why it charged to 83% each time even though I set it at 80% but figured maybe it was battery balancing at the end.

Friday I took a 75 mile trip and plugged in with maybe 60% battery left: the lowest I had drained it so far. When I plugged it in, it charged normally but this time it stopped at 86% for the first time instead of 83%. I'm using a 32A level 2 charger.

Does anyone know the reason why it doesn't stop exactly at the specified max charge setting?

Thanks,
Mike
 

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For us older Bolts, hill top reserve is nominally 90%, but I typically see 87% or 88%. It just seems to not be that accurate at hitting the mark.

Keith
 

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Does anyone know the reason why it doesn't stop exactly at the specified max charge setting?
Our 2017 is normally charged to hilltop level. This varies usually between 87% and 89%...sometimes more. Think of a battery as balloon, not a tank. The capacity at the start can actually be different than the capacity at the end of charging, so hitting an exact percentage is not likely to happen.
 

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Discussion Starter #4
Our 2017 is normally charged to hilltop level. This varies usually between 87% and 89%...sometimes more. Think of a battery as balloon, not a tank. The capacity at the start can actually be different than the capacity at the end of charging, so hitting an exact percentage is not likely to happen.
Not sure I understand the analogy. If I was blowing up a balloon and I had a meter that showed me percentage as I go, I could stop when the meter read 80%. When you have the target set at 80%, it charges past 80%, 81, 82, and stops at 83%. Why couldn't it just stop at 80%?

Mike
 

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I see a similar result with my 2019 Bolt when using the MyChevrolet app to check the charge status. I use time of departure charging and only check it a few hours after i finished - never just after it finishes.

Also as the temperature changes during the day (no driving), inside the garage, I may also see the percent charge change a few points. I often see it rise as the temperature increases. I have no idea why as it is not like a tire where the air expands.
 

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Not sure I understand the analogy. If I was blowing up a balloon and I had a meter that showed me percentage as I go, I could stop when the meter read 80%. When you have the target set at 80%, it charges past 80%, 81, 82, and stops at 83%. Why couldn't it just stop at 80%?

Mike
Because while you are adding air, the pressure is higher. You have to take the measurement when you stop pumping. Real life case, I have a air pump that can stop at set mark. Had it set for 38 psi and it stops when the reading hits 38 psi but then drops to 36 psi. So, I had to set it to 40 psi to get the 38psi for my Bolt.
 

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Not sure I understand the analogy. If I was blowing up a balloon and I had a meter that showed me percentage as I go, I could stop when the meter read 80%. When you have the target set at 80%, it charges past 80%, 81, 82, and stops at 83%. Why couldn't it just stop at 80%?

Mike
My assumption is that the algorithm for capacity, which the percent charge is based on, is constantly being updated. There are lots of things involved. One of those is battery temperature. I sometimes watch it on Torque Pro. I have seen it stop at 88%, and 15 minutes later it says 89%, with the charger not running, but the battery temperature has changed.
 

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Discussion Starter #8
OK. Thanks. Those things I can understand; I do the same thing with my air pump. I can see how it might not have an exact SOC while the charger is still running.

Mike
 

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I have a '19 and have also see discrepancies between the target charge level vs. what it ends up per the My Chevrolet app (e.g. set to "90%" per the graph, might stop at 87%). Batteries never have any sort of output that says "this is my % state of charge". The BMS needs to make some estimate. There are outputs such as the voltage and temperature but that's about it. Hopefully a battery engineer can better chime in on this.

Perhaps the complexities in determining % SoC might be why GM left it out of the car's UI? '11 and '12 Leaf didn't one one either. It only had the 12 fuel bars (we have 20) and guess-o-meter. There were many pleas for % SoC display and Nissan finally added it to model year '13.

If you put no numbers on it and have what look like 5% increments in the dash and the large LCD, then any slight discrepancies in the estimation algorithm/"mysterious moves" aren't noticeable to the user.

I was at a meeting w/the Leaf Chief Vehicle Engineer (Kadota-san) in Dec 2011. Some folks tried to summarize what he said (which I couldn't hear well). There were no videos (I think not allowed and press weren't invited) and I don't recall if photography of the slides was prohibited or discouraged.

See https://www.mynissanleaf.com/viewtopic.php?p=339977#p339977. As I mentioned at https://www.mynissanleaf.com/viewtopic.php?p=239817#p239817, the "mysterious moves" slide the CVE had up said "Nissan strictly confidential" on it, so I didn't want to take a pic of that.
 

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Discussion Starter #11
That video made me forget about battery percentage. Now I have a new question: why did he cut off the top of his steering wheel? ;)

Mike
 
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