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Charging (In)Efficiency

Discussion in 'Cooper SE' started by JZ99, Jan 19, 2022.

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  1. Jan 20, 2022 #41
    insightman

    insightman Well-Known Member Subscriber

    Ann Arbor
    Remember, as @Carsten Haase pointed out, using the EPA's formula of a gallon of gas being equal to 33.7 kWh, the gasoline-equivalent of a fully charged MINI Cooper SE battery is only 0.88 gallons of gas. How many ICE cars can go 177.65 miles on 0.88 gallons of gas?
     
    Last edited: Jan 20, 2022
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  2. Jan 20, 2022 #42
    teslarati97

    teslarati97 Well-Known Member

    It's brutal if you have a foot of snow on your vehicle parked outdoors in -35F weather. The vehicle literally has to idle for 30 minutes to clear off the entire vehicle. Lazy drivers rather get fined by the police because they can't clear the roof on their 3rd row SUV. Mileage can drop 50%+ during a snowstorm.
     
  3. Jan 20, 2022 #43
    JZ99

    JZ99 Member

    If 40% is lost due to charging, then you have to compare to 1.4 gallons. So that's 127 mpg equivalent. I wish I could get that. I think average good-conditions range for this car is around 120 miles, not 178.

    Anyway, the EPA formula is nonsense. The correct way to assess this is miles/$. At 60% charging efficiency, it costs me $6 to fill the battery at standard electric rates. That buys around 2 gallons of gasoline. There are plenty of cars that can go over 100 miles on 2 gallons of gasoline.
     
  4. Jan 20, 2022 #44
    Carsten Haase

    Carsten Haase Well-Known Member

    I'm getting ~85% charging efficiency with my L2 EVSE... If you are really getting 60% it sounds like something is wrong (or maybe the stock MINI charger just sucks?). My long term average in good conditions and more highway than city is 136mi. Not 178 but more than 120.

    Miles/$ may be good for an individual but because the cost of gas/electricity and mpg is so variable it does not make any sense as a published figure. It costs me $3.20 to fully charge my SE which would buy 0.86 gallons of gas. Quite a bit different than you.
     
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  5. Jan 20, 2022 #45
    teslarati97

    teslarati97 Well-Known Member

    There must be more factors involved beyond the level 1 charging from the OP. Is it an older home (and older wires) with a detached garage far away from the main panel?
     

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  6. Jan 20, 2022 #46
    GvilleGuy

    GvilleGuy Well-Known Member

    Greenville, SC
    How are you all getting your charging efficiency? It is the reported kWh from the Mini Charging Sessions app vs what your EVSE shows as going into the Mini?
     
  7. Jan 20, 2022 #47
    chrunck

    chrunck Well-Known Member

    Albuquerque, NM
    I just calculated the charging efficiency on a few trips (I looked at the longest charges in my history) and show 60-66% efficiency. Anyone want to loan me a L2 charger to do a comparison? :p

    The house itself is old, but I ran all the wiring to the detached garage a couple years ago so it's all new wire back to the main panel. The previous owners upgraded to 200A service, and I installed a 60A subpanel in the garage. It's only about 30 feet between the main panel and the garage so I wouldn't think line loss would be that bad.
     
  8. Jan 20, 2022 #48
    chrunck

    chrunck Well-Known Member

    Albuquerque, NM
    I used the formula AndysComputer used on page 2. Percent charged x 28.9kwh / kwh from the charging history.
     
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  9. Jan 20, 2022 #49
    JZ99

    JZ99 Member

    (battery%used*28.9)/(charge kWh)

    I'm using a watt meter for the charge kWh, but it matches the app reported number.
     
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  10. Jan 20, 2022 #50
    JZ99

    JZ99 Member

    I'm measuring the kWh coming out of the wall, so the house wiring is irrelevant. It happens to be a modern house, anyway. The charging load is pulling voltage down from 123V to 121V at 10A. But Watts is Watts. Power Factor is 0.99.
     
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  11. Jan 20, 2022 #51
    JZ99

    JZ99 Member

    Surely, someone with an L2 charger can post some data.
     
  12. Jan 20, 2022 #52
    teslarati97

    teslarati97 Well-Known Member

    It's mostly being indirectly calculated. Some are including the entire battery (usable + buffer) and others are calculating on the usable 28.9kWh such as AndysComputer.

    The losses will be nominal if it's all new (copper) wire and a relatively short distance from the main panel. You could read up the 2017 BMW MiniE tests on bi-directional charge/discharge losses:
    https://www.sciencedirect.com/science/article/pii/S0360544217303730#sec3
     
  13. Jan 20, 2022 #53
    JZ99

    JZ99 Member

    Thanks, good to know.
     
  14. Jan 20, 2022 #54
    Puppethead

    Puppethead Well-Known Member

    Twin Cities, MN
    I still can't understand how this is being calculated. Maybe someone can illustrate with actual numbers? Here's my last (level 2) charge session (outdoors, temperature -3 ºF).

    level2charge.jpg
     
  15. Jan 20, 2022 #55
    JZ99

    JZ99 Member

    For this case:

    (66%-52%)*28.9/4 = 101%.

    Nice, you created energy!

    Since they round the %, and the kWh, it's not very accurate for short charges. But this is clearly way better than I'm getting using L1!
     
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  16. Jan 20, 2022 #56
    chrunck

    chrunck Well-Known Member

    Albuquerque, NM
    Sure, you charged 14% of the battery (66% - 52%), and it used 4 kWh of juice. 14% of the total battery is 4.046 (0.14 x 28.9). The efficiency is 4.046 / 4 = 101% efficiency. Your house is magic!
     
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  17. Jan 20, 2022 #57
    chrunck

    chrunck Well-Known Member

    Albuquerque, NM
    Who was the person on here that received two different chargers with their MINI? I'd be curious to see how the other charger is performing.
     
  18. Jan 20, 2022 #58
    JZ99

    JZ99 Member

    Hey, I'm in Twin Cities too (Victoria). How's your mileage in these sub-zero conditions? Yesterday, my wife got a whopping 2 miles/kWh (1.3 measured at the wall).
     
  19. Jan 20, 2022 #59
    AndysComputer

    AndysComputer Well-Known Member

    Plano, TX
    No there aren't.
     
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  20. Jan 20, 2022 #60
    teslarati97

    teslarati97 Well-Known Member

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