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Can someone PLEASE explain how rated range is calculated.

Discussion in 'Model S: Battery & Charging' started by wormhole, Sep 30, 2013.

  1. wormhole

    wormhole Banned

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    photo.JPG
    Please look at the above photo. When I unplugged my car and got in for the trip, I had 180 rated miles left in the battery. As you can see, I drove 81.4 miles, used 24.1 kWh, and averaged 296 wh/mi. Yet when I finished I had 93 rated miles of range left. I still lost 5 miles of rated range vs actual range despite averaging less than the 308 wh/mi i thought went into the 265 rated mile range calculation.

    I have asked [email protected] numerous times about this, using numerous trips with similar results. I have never gotten a straight answer, and in most cases the 'response' has been to highlight logs for an entire day which is completely irrelevant to the question. For clarity, again, I unplugged the car and drove off, there was no vampire loss. Any explanation would be greatly appreciated. Thanks.
     
  2. jerry33

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

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    As far as I know, rated range is just the EPA number. The way it works for me is:

    1. Charge car to some amount e.g. 210 miles.

    2. Drive a bit say 50 miles.

    3. Subtract some vampire e.g. 5 miles.

    4. Add some gains e.g. 8 miles.

    5. Balance at the end of the day 163 miles.

    If we use your numbers to obtain the vampire loss:

    1. 180 miles

    2. minus 81.4 miles = 98.6 miles

    5. minus 93 miles

    3. equals 5.6 miles vampire loss.
     
  3. wormhole

    wormhole Banned

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    There is no vampire loss when you immediately start driving the car when you unplug it. Plus you 'added gains' to your calculation, not sure what that is, or why you'd end up using less rated miles than actual miles driven while I would use more...
     
  4. stopcrazypp

    stopcrazypp Well-Known Member

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    #4 stopcrazypp, Sep 30, 2013
    Last edited: Sep 30, 2013
    This owners only thread is supposed to explain it:
    http://www.teslamotors.com/forum/forums/important-new-information-about-rated-miles-and-projected-miles

    But paraphrasing others that have access to it:
    http://www.teslamotorsclub.com/showthread.php/17590-Model-S-Battery-Pack-Cost-Per-kWh-Estimate/page27?p=411509&viewfull=1#post411509

    Here's another reference that tries to explain the situation (although it's not 100% certain):
    https://docs.google.com/document/d/1nlZhDYtCinX_Wkb9OST-QBzervVp5yABMVBS266Q3W4/pub#h.1e9ai734m71s
     
  5. wormhole

    wormhole Banned

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  6. yobigd20

    yobigd20 Well-Known Member

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    it's a calculated algorithmic guess and it's near impossible to be 100% accurate.

    To learn more about the actual calculation itself, you're going to want to read these thoroughly:
    Patent 20100138178: "Battery capacity estimating method and apparatus" Battery capacity estimating method and apparatus - Patent application
    Patent 20110156641: "STATE OF CHARGE RANGE" http://www.faqs.org/patents/app/20110156641


    or, rather, my simplified explanation - "it's complicated". lol.
    but honestly, 5 miles range loss? that's a hell of a lot better than mine. It takes me 135 rated range miles to drive 100 actual miles. but I don't drive anywhere near the speed limit either. ;)
     
  7. scaesare

    scaesare Active Member

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    I started THIS THREAD a while back to discuss this. It might shed some light on the discrepancies we see...
     
  8. jerry33

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

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    To put a nice face on it, lets call it auxiliary system use.

    If I start with 210 miles, drive 50, and end up with 170 miles (for ease of calculation), I've gained ten miles over the rated range.

    The reason that one person might use more and the other one less is how many Watt hours per mile they use. If 308 Wh/mi is equal to rated range, then someone using 340 Wh/mi would get less and someone using 255 Wh/mi would get more. If you use exactly 308 and get less than rated range then either the calculation is out, the Auxiliary systems are using some, or a combination of both.
     
  9. wraithnot

    wraithnot Model S VIN #5785

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    The slightly screwy method to calculate rated range makes a lot more sense if you consider that there is some uncertainty in calculating exactly when the car will need to shut down, but people will be REALLY unhappy if the car stops when there is 5 miles left on the gauge and that people will also be very unhappy if they pay a whole lot of money for a car with 265 miles of range, but the gauge shows significantly less when they fully charge it.

    If a fully charged car shuts down on average after 265 miles of 308 wh/mi that means sometimes it will shut down after a few more than 265 miles and sometimes it will shut down after a few less than 265 miles. So you have to make the gauge show zero after less than 265 miles of 308 wh/mi so you can be really confident it will never strand someone with more than zero on the gauge. But you can't do that simply by subtracting miles from the gauge or it will never show the full 265. Thus the strategy of showing 265 when full, but removing miles from the gauge faster than you would for 308 wh/mi.

    The most accurate way to do things would be to show 265 when full, remove miles of range corresponding to 308 wh/mi, and somehow represent the uncertainty of when the car will actually stop moving. But that would probably confuse the hell out of people. So they do something slightly sneaky that gives them the behavior they want and will only confuse the hell out of people if they really try to dig into the details ;-)
     

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