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How does the US EPA calculate the "Certified Range" of an EV?

Discussion in 'Model S: Battery & Charging' started by ecarfan, Dec 25, 2013.

  1. ecarfan

    ecarfan Well-Known Member

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    Does anyone know how the US EPA calculates the "Certified Range" of an EV? I have searched the EPA website and can't find information about that. Ran a Google search but still can't find it.
     
  2. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    It appears that they use SAE J1634 multiplied by a fudge factor according to the epa.gov site
     
  3. stopcrazypp

    stopcrazypp Well-Known Member

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    #3 stopcrazypp, Dec 25, 2013
    Last edited: Dec 25, 2013
    This FOIA request details the test procedure (SAE J1634 as jerry says):
    http://www.smidgeindustriesltd.com/leaf/EPA/EPA_test_procedure_for_EVs-PHEVs-1-13-2011.pdf


    Long story short:
    1) fully charge car
    2) park it overnight (factors in "vampire" losses)
    3) test on given test cycle repeatedly until car can't keep up (either stops completely or can't meet the parameters of test; keep in mind that whatever the car's dash says about range is irrelevant to this as long as it can keep driving)
    4) fully charge car from an AC source and measure electricity used (charging losses are already factored in)

    This procedure gives you the range (which is a "combined" number) and also the efficiency numbers on the sticker.

    As for the adjustment jerry33 mentioned, it no longer applies for any vehicle after the 2012 model year as all cars have to use the new 5-cycle procedure now:
    http://www.caranddriver.com/features/the-truth-about-epa-city-highway-mpg-estimates-measuring-fuel-economy-page-2
     
  4. ecarfan

    ecarfan Well-Known Member

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    Thanks for the links. The third page of the Car and Driver article discusses rating EVs:

    QUOTE: Pure electric cars, such as GM’s EV1 of the 1990s and, more currently, the Tesla Roadster, have fuel economy stated in units of kilowatt-hours (kWh) per 100 miles. For example, the Tesla gets 32 kWh per 100 miles city and 33 highway, but these figures are Greek to American car buyers accustomed to miles per gallon. Which is better, 100 mpg or 32 kWh/100 miles? Everyone involved, including the automakers, seems to agree that all cars, including electrics, need to be rated on a mpg-equivalent basis where, for example, the amount of energy used by an electric vehicle could be converted into a volume of gas with the same energy content. All window stickers would then contain mileage figures in mpg. The EPA is currently in long, soul-searching meetings to agree on a standard; a draft proposal should be submitted by year’s end. Whatever the specifics, GM expects the Volt to carry a fuel-economy rating of well over 100 mpg.
    -----------------------------------

    However, the article doesn't specifically discuss the procedure used by the EPA to arrive at the Rated Range figure. I will look up the SAE J1634 standard.
     
  5. stopcrazypp

    stopcrazypp Well-Known Member

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    The SAE J1634 standard is already described in the PDF link I gave and I outlined the procedure in my comment above. Is there anything else that's not clear about it (I think I covered most of it)?
     
  6. ecarfan

    ecarfan Well-Known Member

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    Okay, thanks, my confusion!

    I found this document at http://www.smidgeindustriesltd.com/leaf/EPA/EPA_test_procedure_for_EVs-PHEVs-1-13-2011.pdf

    QUOTE: Electric Vehicle - City Test Procedure Summary - Following SAE J1634 Recommended Practice, the battery is fully charged, the vehicle is parked over night, and then the following day the vehicle driven over successive city cycles until the battery becomes discharged (and the vehicle can no longer follow the city driving cycle). After running the successive city cycles, the battery is recharged from a normal AC source and the energy consumption of the vehicle is determined (in kW-hr/mile or kW-hr/100 miles) by dividing the kilowatt-hours of energy to recharge the battery by the miles traveled by the vehicle. To calculate the energy consumption in units of mpge (miles/gallon equivalent) we use a conversion factor of 33.7 kilowatt-hours of electricity per gallon of gasoline (which is basically a measure of the energy in gasoline (in BTUs) converted to electricity). The city driving range is determined from the number of miles driven over the city cycle until the vehicle can no longer keep up with the driving cycle.
    Electric Vehicle – Highway Test Procedure Summary - The same test SAE J1634 procedure outlined above, is used determine the highway energy consumption and the highway driving range (except the vehicle is operated over successive highway cycles)
    ------------------------------------------------
     
  7. cwerdna

    cwerdna Active Member

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    I posted some links long ago about the EPA tests (including a link to that C&D article) for ICEVs at Car and Driver: The Truth About EPA City / Highway MPG Estimates | PriusChat. Detailed Test Information has info about the cycles.

    Obviously, using bags to collect exhaust gases and then derive FE from that won't work for BEVs. :)

    There's also the caveat of deriving values based upon averaging the results of charging to 80% and 100%. See 2013 Nissan LEAF Rated At 75 Miles. But 84 Miles Using The Outgoing 2012 EPA Ratings System. Off the top of my head, I don't know of the Model S went thru that.
     
  8. stopcrazypp

    stopcrazypp Well-Known Member

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    I don't think it's a coincidence that immediately after the EPA announced they would be doing such range averaging, Tesla updated the Model S so that there is no longer two distinctive modes, but rather the user can select their own desired SOC.
     
  9. miimura

    miimura Active Member

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    Agreed. "Standard" and "Range" charge settings were just begging for the EPA to average them to give a lower range figure. RAV4 EV and Leaf were both bitten by this.
     
  10. David_Cary

    David_Cary Member

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    Yeah - I always wondered whether this was genius (ability to make quick changes) or just dumb luck.

    The 80/100 averaging is just another example of really stupid government decisions.
     
  11. Theshadows

    Theshadows Active Member

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    #11 Theshadows, Dec 28, 2013
    Last edited: Dec 28, 2013
    What they should do it levalize it at btu's. 114000 btu's in a gallon of gasoline. 3412 in a kWh. Using btu's for the conversion there are 33.4 kWh in a gallon of gasoline. :).

    Thus using this true unit of energy our cars can go 95.4 miles on the same number of btu's that are contained in a gallon of gasoline.
     
  12. woof

    woof Model S #P683 Blue 85 kWh

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    I think you are off by a factor of 10. The EPA's "MPGe" uses 33.7 kWh/gallon Miles per gallon gasoline equivalent - Wikipedia, the free encyclopedia. The Model S is EPA rated at 89 MPGe according to the window sticker.
     
  13. Theshadows

    Theshadows Active Member

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  14. ecarfan

    ecarfan Well-Known Member

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    #14 ecarfan, Jan 2, 2014
    Last edited: Jan 3, 2014
    So that is how the EPA arrives at the 265 figure that they assigned to the Model S. I wonder if to "fully charge" the S the EPA slid the setting on the charge "bar" all the way to the right and then let the car charge? Or is that not the only way to tell the car to charge to the maximum possible level?
     
  15. Kipernicus

    Kipernicus Model S Res#P1440

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    Will the EPA test new "2014" model year cars?
     
  16. ecarfan

    ecarfan Well-Known Member

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    This description makes it sound like the EPA would publish two MPGe and range figures for the Tesla, a city and a highway figure, like they do for ICE cars. But I am only aware of one set of figures, 89 MPGe and 265 miles range. So I don't know if those numbers are for the city cycle testing, the highway cycle testing, or an average of the two.
     
  17. stopcrazypp

    stopcrazypp Well-Known Member

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    There's actually three published figures: city, highway, and combined (which is 55% city and 45% highway):
    http://www.fueleconomy.gov/Feg/bymodel/2013_Tesla_Model_S.shtml

    There is, however, only 1 range figure and that's based on the "combined" rating. You can figure out the city and highway range figures though by doing some simple math.

    And they arrive at those figures actually through 5 different test cycles (not just the two indicated in that document, which is a bit outdated):
    http://www.fueleconomy.gov/feg/fe_test_schedules.shtml
    As you can see in the link above, in addition to the old city and highway cycle, there is now "high speed", "air conditioning", and "cold temperature" cycles to offer a more realistic rating.
     
  18. miimura

    miimura Active Member

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    You will also notice on that page that the Model S 60kWh is rated at 94/95/97 City/Combined/Hwy, notably higher than the Model S 85kWh at 88/89/90mpge. Also, the kWh/100mi number of 38 combined for the MS85 appears to be high because it includes the charger losses as mentioned earlier. 1/(38/100)=2.63mi/kWh. The car will always show more miles/kWh because it's only telling you how much energy it took out of the battery, not the energy out of the grid as the EPA calcs do.
     
  19. ecarfan

    ecarfan Well-Known Member

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    Okay, so let's see if I've got this right:

    According to that page, the EPA rates the S85 at 38KwH/100 miles "combined" which is 0.38KwH/mile

    To convert that to miles of range, assuming that we can use all of the 85Kw battery (which of course we are prevented from doing so by the software), divide 85KwH by 0.38KwH/m to get about 224 miles. Which doesn't seem right. What am I missing here?

    Thanks!
     
  20. David_Cary

    David_Cary Member

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    The 85kwh in the battery takes closer to 95 kwh to get so that is why the range does not match the "mileage".
     

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