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Wh/mi vs Environment Temperature

Discussion in 'Model S: Battery & Charging' started by dmckinstry, Jul 13, 2015.

  1. dmckinstry

    dmckinstry Model S - U.S. P - #1649

    Joined:
    Jul 9, 2011
    Messages:
    903
    Location:
    Medical Lake, WA (near Spokane)
    I've scanned the temperature management threads, but didn't notice this being addressed.

    The northwest has been experiencing a heat wave for the past 3 or 4 weeks, but it's finally cooled off again.
    I've noticed that when the temperatures have been up between 90-105F my average Wh/mi have been at least 30 Wh/mi higher than when the temperature has been below 80F (for similar driving pattern). At the higher temperatures I've been getting over 300 Wh/mi, but now that it's cooled down, I'm getting about 265 Wh/mi. In using EVTripplanner, no such extreme difference is indicated. Is my observation just an anomaly, or is the temperature management system working that hard to keep the temperature down? Does anyone know what temperature the management system attempts to keep the battery, etc. below?
     
  2. ChadS

    ChadS Petroleum is for sissies

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    #2 ChadS, Jul 13, 2015
    Last edited: Jul 13, 2015
    Tesla doesn't like to tell us exactly how this stuff works. Partly so they can change it, I assume.

    I don't know at what temperature the system starts trying to keep the batteries cool, but it does seem that in the distant past I have heard fans running around 90 degrees that I don't normally hear - even when I had the HVAC turned off. (I haven't driven the car much in the recent heat wave; my wife has had it). Obviously this is affected by more than ambient temperature; it also depends on how hard you've been driving the car, whether and how fast you are charging, etc. SOC and even humidity can play a part as well.

    If you look at Tesla's range calculator HERE, it seems to indicate that with HVAC off, the warmer it gets (at least up to 110 degrees, which is the highest setting) the more miles you can get out of the car. Of course, it could still be using more Wh/mi; it may just be that more energy can be pulled out of the pack at those temperatures. If you had HVAC off, that seems counter to your experience. If you had HVAC on, it seems your extra use in the heat may have been largely for cabin AC.

    The most interesting thing (to me, anyway) is that if you set the calculator to turn HVAC on, now the best temperature is not 70 as I suspected, but rather 50. (There is no setting on the calculator between those two temperatures). 70 seems much closer to a normal cabin temperature, plus AC uses a heat pump and generally uses less energy, plus you can get more energy out of the battery at a warmer temperature, so I find that surprising.

    Sorry, no answers, just more questions...
     
  3. dmckinstry

    dmckinstry Model S - U.S. P - #1649

    Joined:
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    Location:
    Medical Lake, WA (near Spokane)
    At least Chad, thanks for pointing me to the range calculator. I have been using the AC, but not all the time.
     

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