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Discussion Starter #1 (Edited)
I compared 24 months of data for the my 2017 gen2 Volt Jan 2017 through Dec 2018 against 24 months with my gen1 Volt. I bought my gen2 Volt Dec 30th 2016. The gen1 data covered Jan 2016 through Dec 2017.
Its kind of a cool chart because it shows a bunch of different things.

  • The gen2 is better, but of course I park my gen2 at work in a covered garage and my gen1 parked in the sun
  • With the hot Austin summers the mpge from the plug hits a minimum of ~110mpge in August due to the AC, and the battery TMS cooling when charging.
  • A second minimum of 111-112mpge occurs in Dec and Jan. Austin has mild winters, but occasional cold snaps require battery power to heat the car. Gen2 heated seats helps.
  • The most efficient months are March and Oct/Nov when the mpge ~121-122mpg and little heating or cooling is required
  • Overall my gen2 mpge ~115mpge compared to EPA 106mpge. 240v charging is more efficient, more so on the gen1 than the gen2. Both cars were primarily charged on my ClipperCreek at home at 240v overnight with daytime charging as needed; along with occasional opportunity charging while traveling or locally.



Here's the equivalent inverted chart for watt hours per mile. mpge=33.7/whm. I gathered the data from mychevrolet.com, filling in missing charge events based on the screen displays kwh/mpge display along with fudge factors based on that months data. My chevrolet has gotten increasingly unreliable the last week of 2018; although a similar unreliable period occured in Dec 2017, Jan 2018. For both gen1 and gen2, I calibrated mychevrolet against Chargepoint; gen2 is spot-on; gen1 was low by 2.5%-3% so I adjusted the gen1 data slightly. My gen2 has 19300 EV miles (86% EV) in 24 months. My gen1 had about 15000 EV miles during the 24 month period.


Overall, my gen2 mpge is about 8.5% better than the gen1. I also tracked mpg; gen2 gets about 10% better ICE mpg than the gen1; 39mpg vs 35mpg mostly on interstates.
 

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Interesting data, but I have a question. What is the primary contributing factor to why mpge is better with the Gen2 compared to the Gen1? Surely mpge is independent of charging voltage. Did the Gen2 get a more efficient electric motor or better regen brakes?
 

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Discussion Starter #3 (Edited)
Interesting data, but I have a question. What is the primary contributing factor to why mpge is better with the Gen2 compared to the Gen1? Surely mpge is independent of charging voltage. Did the Gen2 get a more efficient electric motor or better regen brakes?
GM estimated 106mpge vs 98mpge or 8% improvement overall. The imrpovement would be some combination of:
  • charging efficiency
  • drive train efficiency (EV motors efficiency and lower resistance). Gen2 has new EV motors; gen2 is lighter
  • improved mechanical efficiency in planetary gears, drive train, tires
  • regen efficiency (due to improved mechanical efficiency and EV motor efficiency)
  • improved climate control AC/heat efficiency, TPMS battery cooling efficiency

Charging overhead is reduced for gen2 on 120v; smaller improvement on 240v. I charge on 240v. On gen1 I measured additional overhead at 120v due to I^2R losses for more hours compared with 240v. There was more additional overhead at 120v in hot weather due to battery TPMS cooling. So mpge depends on charging voltage.
 

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There are many unaccounted for variables. Although the Gen 1 and Gen 2 Volt were both driven in Austin, TX the work destination is not the same, terrain and average travel speed may be a factor. The driver was more experienced by the time they started driving the Gen 2 Volt, less likely to make excessive use of the accelerator pedal. Year to year variations in temperature may be factor. The Gen 2 Volt is 200 lbs lighter than the Gen 1 Volt.
 

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Interesting data, but I have a question. What is the primary contributing factor to why mpge is better with the Gen2 compared to the Gen1? Surely mpge is independent of charging voltage. Did the Gen2 get a more efficient electric motor or better regen brakes?
If charging voltage influences charging efficiency, then it would also impact MPGe.

The energy content of 33.7 kWh of electricity "from the wall" = one "energy equivalent gallon" of electricity (1 Ge). The Gen 2 Volt is rated at 106 MPGe. The 53 ev mile/per charge rating indicates the Gen 2 Volt pulls 0.5 Ge, or 16.85 kWh of power "from the wall," to put enough energy content into the battery to drive 53 ev miles.

While pulling 16.85 kWh of power "from the wall," ~2.65 kWh of that power will be used in the charging circuits, and ~14.2 kWh will be stored as usable power in the battery. That ~14.2 kWh of usable grid power in the battery then enables you to drive 53 rated ev miles on one full charge.

The amount of power you pull "from the wall" to put 53 miles of rated ev range into your battery depends on the efficiency of the charging system. If L1 charging is a bit less efficient than L2 charging, then more energy content (i.e., more than ~2.65 kWh) will be used in the charging circuits, requiring more than 16.85 kWh to be pulled "from the wall" to fully charge the battery with the ~14.2 kWh used to obtain 53 miles of rated ev range. IOW, driving 53 ev miles on that particular charge = driving 53 miles on 0.5+ Ge of power from the wall, reducing the MPGe below 106.
 

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Discussion Starter #6 (Edited)
If charging voltage influences charging efficiency, then it would also impact MPGe...
While pulling 16.85 kWh of power "from the wall," ~2.65 kWh of that power will be used in the charging circuits, and ~14.2 kWh will be stored as usable power in the battery. That ~14.2 kWh of usable grid power in the battery then enables you to drive 53 rated ev miles on one full charge.
...If L1 charging is a bit less efficient than L2 charging, then more energy content (i.e., more than ~2.65 kWh) will be used in the charging circuits, requiring more than 16.85 kWh to be pulled "from the wall" to fully charge the battery with the ~14.2 kWh used to obtain 53 miles of rated ev range.
The gen2 Volt's internal kwh used while driving meter isn't perfect, but the results seem consistent with themselves. Typically, on 240v I see 12.5% overhead. So 15.98kwh from the wall to charge 14.2kwh into the battery. My gen2 typically shows 14.0kwh used on a full charge, with full charges varying from 17.0kwh in August for 21% overhead due to TPMS cooling the battery in a very warm garage, to a minimum of 15.24kwh when the car showed using 13.9kwh in March for about 9.6% overhead.

On one gen2 120v charging event at 12amps I saw 16.9% overhead; mild temperatures without TPMS; so maybe there's a 3% mpge improvement when charging with an L2 at 240v???? (120v, 12amps compared with 240v, 15amps)
 

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Overall, my gen2 mpge is about 8.5% better than the gen1. I also tracked mpg; gen2 gets about 10% better ICE mpg than the gen1; 39mpg vs 35mpg mostly on interstates.
Great data! I wonder if this consistent difference for both ICE and EV is mostly the OEM tires.
 

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I compared 24 months of data for the my 2017 gen2 Volt Jan 2017 through Dec 2018 against 24 months with my gen1 Volt. I bought my gen2 Volt Dec 30th 2016. The gen1 data covered Jan 2016 through Dec 2017.
Its kind of a cool chart because it shows a bunch of different things.
Perhaps you could explain how your 12-month graph is intended to represent 24 months of data.

Perhaps you could explain how you determined the MPGe for the graphs. Data from OnStar likely includes all power drawn from the wall, which would include power used to precondition the car and to maintain the battery. Data from your home charger unit would not include any charging done away from home, but would include power used for preconditioning and battery maintenance while plugged in at home.

Many who precondition using L2 charging might leave the car plugged in long enough after preconditioning for the battery to be "topped off" before unplugging, resetting the car’s display to zero, and when that happens, preconditioning and battery maintenance power consumption doesn’t show up on the energy usage screen’s trip MPGe display numbers.

IOW, the MPGe numbers appearing on your Volt’s energy usage display screen might be higher than the MPGe numbers from the OnStar data because they don’t include all of the Volt’s wall power consumption. Since neither version excludes ev miles driven using the electric energy content of the regen created during the driving (i.e., electric miles driven not using grid power), which version is the more useful?
 

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Discussion Starter #9 (Edited)
Perhaps you could explain how your 12-month graph is intended to represent 24 months of data...

Perhaps you could explain how you determined the MPGe for the graphs. Data from OnStar likely includes all power drawn from the wall....

IOW, the MPGe numbers appearing on your Volt’s energy usage display screen might be....
For each car, I averaged two January's, two February's, ... two Decembers. The averaging improves the quality of the data. mpge is just 33.7/kwhm.

I have never used preconditioning. The coldest my garage ever gets is in the upper 30's to low 40's when its a rare hard cold snap in Austin with temps in the teens outside; the garage is usually in the upper 50's in the morning in the winter. In the summer, my garage is often in the 100's, but the AC cools off quickly since the garage is shaded.

The mpge display in the car's display seems to assume a 19% overhead. My measured overhead in mild weather is usaually 12.5%, and perhaps 21% depending on battery TPMS in hot weather. So in mild weather the mpge in the car is pessimistic showing a lower mpge than actual mpge. In the summer's hot weather the car's mpge is a little bit optimistic. Perhaps the car's mpge display assumes 120v charging with higher charging overhead.
 

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For each car, I averaged two January's, two February's, ... two Decembers. The averaging improves the quality of the data. mpge is just 33.7/whm.

I have never used preconditioning. The coldest my garage ever gets is in the upper 30's to low 40's when its a rare hard cold snap in Austin with temps in the teens outside; the garage is usually in the upper 50's in the morning in the winter. In the summer, my garage is often in the 100's, but the AC cools off quickly since the garage is shaded.

The mpge display in the car's display seems to assume a 19% overhead. My measured overhead in mild weather is usaually 12.5%, and perhaps 21% depending on battery TPMS in hot weather. So in mild weather the mpge in the car is pessimistic showing a lower mpge than actual mpge. In the summer's hot weather the car's mpge is a little bit optimistic. Perhaps the car's mpge display assumes 120v charging with higher charging overhead.
Sorry, I don’t understand your reply. Did you calculate the January 111-112 MPGe numbers, etc., or are monthly MPGe mileage numbers available from some source as part of data compiled from the car’s computer? And if so, how are they calculated?

I’m not sure what you mean by "mpge is just 33.7/whm." "MPGe is 33.7 somethings or other per watt hour mile"(?). MPGe is not a fixed number, but a fuel mileage calculation, i.e., the electric distance you drive divided by the number of gallons of "energy equivalent" electric fuel (Ge) you use to drive that far. If you drove 53 electric miles by pulling 0.5 Ge of electricity from the wall (some of which was used in the charging circuits, some of which was used as motor fuel), you drove 53 ev miles using 0.5 Ge, and your MilesPerGe = 106.

Why do you think the MPGe display in your car’s display is assuming a 19% overhead? Can you provide an example of how a 19% overhead will give you the MPGe number shown on the display? If the car’s computer tracks the amount of power pulled from the wall to fully charge the battery, it should incorporate any differences in charging efficiency (i.e., differences in charging losses) into the calculations that produce the MPGe.
 

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Discussion Starter #11 (Edited)
Sorry, I don’t understand your reply. Did you calculate the January 111-112 MPGe numbers, etc., or are monthly MPGe mileage numbers available from some source as part of data compiled from the car’s computer? And if so, how are they calculated?

I’m not sure what you mean by "mpge is just 33.7/whm."
...
Why do you think the MPGe display in your car’s display is assuming a 19% overhead? Can you provide an example of how a 19% overhead will give you the MPGe number shown on the display?
I had a typo; mpge=33.7/kwhm=33700/whm; which I calculated from the energy usage and the miles driven; there were a few missing charge events on mychevrolet which I filled in by hand. I tracked it in an excel spreadsheet. I got the miles driven from voltstat's or equivalently from the car's trip-a odometer.

Let's say it is a mild spring day and I drove 56 miles using 14kwh on the car's display, and the car's mpge displayed 113mpge. According to mychevrolet I used 15.75kwh from the plug. From the battery, (14kwh/56miles)*(1000wh/kwh)=250wh/m. From the plug (15.75kwh/56mile)*(1000wh/kwh)=281wh/mile.

Then my car's actual mpge=33700/281=120mpge. The car's mpge panel is 113mpge, which is equivalent to 33700/113=298wh/m from the plug, which is a little higher than the actual value of 281wh/m from the plug.

The actual charging overhead is 281whm/250whm=1.124 or 12% charging overhead
The car's internal display mpge=298whm/250whm=1.192 or 19% charging overhead
 
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