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Discussion Starter #1 (Edited by Moderator)
I've had my new 2017 Volt for several weeks now and I've run into a slight concern. I live at the top of a fairly sizable hill/mountain, which means that when I leave home, I start my trip with a good run of driving in L and/or with light to moderate use of the break pedal on the way down. (It's a windy drop, and slowing down is required most of the way.) Under current early fall weather conditions, that's been equating to about 8 km of range added to my EV meter by the time I reach the bottom. My concern lies in doing this with my car already at a full state of charge (and with a trend that's seems to have developed now that I've done it several times).

The first time that I did it, my car started at full charge, showing 85 km of range (as manufacturer specified), and gained 8 km more on the way down. (I understand that the Volt's battery operates with somewhat fuzzy min and max charge parameters, so this didn't initially concern me, and I was happy to see that the descent wasn't all just wasted energy.) The next time that I fully charged the car, however, the range that the car showed was now 92 km, and it once again gained another 8 km on the way down. On round three, the fully charge EV range showed 96 km, which topped out at 104 km of range by the time I reached the bottom of the hill. (I have since held off on letting my car fully charge at home. However, I have managed to fully charge it at work on a particularly long day, and it again showed 96 km at full charge. This seems to be the new full SOC number.)

So, am I potentially overcharging my battery by fully charging it and then driving down my hill; and, if so, are there any ways to mitigate the problem aside from fiddling with the charge timings so that it's never fully charged at home? (I know that if the battery actually does reach too full a charge, it could start affecting its longevity.) Or is this just a case of the Volt's math getting screwed up, and it only thinks the range/charge is going up that high (in which case, is there any way to reset things so that I have a more accurate estimation of it's actual EV range/charge)?

Any help/insight would be greatly appreciated! (I really don't want to degrade the battery on this thing. I plan on holding onto it for quite some time.)
 

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Simple answer is no. There is no way that you can overcharge your HV battery. The Volt engineers thought of that and your Volt has a way of bleeding off the extra incoming power so that it does not get to the battery.
 

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TSquare has it right. The Volt runs the two motors in opposition if necessary. No need to worry. The change in range you're seeing is all about the estimate. Also note that unless the drop is significant, the energy you use may be greater than the energy you get from the drop in elevation.
 

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Discussion Starter #4
...Er, so I wrote this, realized that I'd goofed and been making the break/brake typo error, corrected the errors (the subject title included), had a weird page timeout error, redid the post using a copy of the, I assure you, corrected text, posted it and... this older, uncorrected version somehow went up. So, yay gremlins???

P.S *brake...sigh
 

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It's more than likely that your Volt is not adding significant amounts of energy into the battery, rather the range estimate ("guess-o-meter") is updating according to current driving conditions. Normal range indication on my Volt is ~60 km however after a long decent on the Coquihalla highway it will display 90 km following the next charge. I still get the exact same 10.3 kWh of electricity that I've been getting for 4 years.
 

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Discussion Starter #6
@ TSquare, DonC & Rampage_Rick,

Hey. Thanks for the lightning-fast replies! ;)

It's good to get confirmation that this isn't an issue. I figured it wasn't something that the engineers would have overlooked, but as the trend continued, and having that little number hit 104 (22% over normal full SOC was starting to look pretty significant), it was beginning to make me a little uncomfortable

So, the EV km number is all just the car projecting some loosey-goosey-math estimate, then. Too bad there wasn't some way to check the battery's actual charge percentage (although, I suppose with some of it's fuzzy charge parameters, you'd probably get a fairly high rate of people misunderstanding things, or second-guessing the car's management routines).
 

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Too bad there wasn't some way to check the battery's actual charge percentage (although, I suppose with some of it's fuzzy charge parameters, you'd probably get a fairly high rate of people misunderstanding things, or second-guessing the car's management routines).
Actually, there is a way to look at the actual charge. Get yourself an OBII reader and an app for your phone to read it. I have Torque Pro and MyGreenVolt.
 

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Keep in mind that the "full charge" range estimate is based on the data the computer has gathered over time on your driving habits (using an algorithm to calculate full charge range as historical average electric mileage multiplied by the amount of full-charge usable power). Once you start driving, the Volt makes "on the fly" battery soc and mileage estimates, and then adjusts the estimated range for the current driving conditions. IOW, you didn’t necessarily add 8 km’s worth of regen to the existing battery supply by driving downhill, you just improved your "on the fly" electric mileage by the time you reached the bottom of the hill. The better mileage meant you could drive further on the available power. Even if you used a dab of power to drive downhill and thus had less power in the battery than you did at the top of the hill, the computer is projecting a range increase based on the assumption that you are going to keep driving downhill and getting that great downhill electric mileage. That estimate will decrease once you start driving again on level terrain.

The Volt will stop charging ("full charge") when a programmed battery state of charge level has been reached (~87% for my 2012 Volt). A small buffer above that retains the capacity to accept additional charging, so those in your situation who might immediately drive downhill on a full charge will be able to put some downhill regen into the battery, increasing the soc above the "full charge" point. My understanding is that there is a certain "maximum allowable soc" (perhaps in the low 90s%?), and under certain conditions when the downhill portion is long and/or steep, regen may continue until that extra upper buffer is full, at which point the car’s usual practice of recharging the battery via braking regen cannot continue (other threads are available to explain how the Volt deals with the "maximum allowable soc level reached" condition). The numbers on the usage screen should now transition out of Electric Mode. You’re not using grid power, and you’re not allowed to put any additional regen into the battery, so the distances driven in this condition cannot be counted as "Electric" km. For the remaining part of downhill descent (i.e., until you’re actually using power from the battery again), the distances driven will likely register as "Gas" km. If you’re still recording distances as "Electric" km as you reach the bottom of your hill, it suggests you haven’t completely filled that extra buffer, and the increased range estimate is likely a result of the improved mileage obtained by driving downhill.
 

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...Er, so I wrote this, realized that I'd goofed and been making the break/brake typo error, corrected the errors (the subject title included), had a weird page timeout error, redid the post using a copy of the, I assure you, corrected text, posted it and... this older, uncorrected version somehow went up. So, yay gremlins???

P.S *brake...sigh
Yep. Oxymoron is "regeneration" and "breaking" in juxtaposition. ;)

The advice here is correct. GM battery management is extremely good and very conservative.
 

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I wonder if the estimating software now has bugs in it if its ever increasing and say there is really no more room to save the extra down hill energy generated because it seems to be capturing and estimating what it thinks is increasing range. To me if the car is going down hill and it is NOT storing the energy because it can't they should NOT be increasing the estimated range. A system test issue!
 

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It won't hurt anything but why waste energy? Why don't you stop charging before the battery is fully charged and let the regen at the start of your trip finish charging up your battery?
 

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It is very unlikely that any energy is being wasted, even when you leave with a full charge.

The range estimate you are seeing is not just a function of how full the battery is, it is also a function of how efficiently you drive, and in what conditions. In other words, the km estimate factors in kWh left in the battery as well as the kWh/mile (or km) you are averaging.

The Volt has plenty of buffer in its battery to accommodate going down a hill for a little bit and recapturing some energy in the process. But if you really want to test it sometime, leave your house with, say, half a charge. Put the center stack on the energy usage screen to see kWh used and take note of it. As you go down the hill, that number will decease. It is highly unlikely that it will decrease any more than 0.5 kWh, 1 kWh at most, and the Volt has a larger buffer than this anyway that remains unused (except when some of it gets used in these 'corner case' scenarios).
 
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