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real world range vs ambient temperature?

Discussion in 'Model S: Battery & Charging' started by ljwobker, Mar 6, 2014.

  1. ljwobker

    ljwobker Geek.

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    I'm assuming that in the Model S, at some point as the ambient temperatures start to fall there is a *non linear* increase in how much energy has to be used to keep the battery warm and the cabin tolerably comfortable (which is, of course, somewhat subjective). Can anyone provide input on roughly where this curve starts to get steep? My educated guess would be that 50F is probably not too bad, but 10F is probably quite a meaningful impact.... what I'm really interested in is what sort of behavior we get between these two numbers. I'm fortunate enough to live somewhere that's rarely below freezing, but we do get a lot of days between 30-50 so I'm trying to estimate what sort of behavior I'll see in the winter here.
     
  2. Doug_G

    Doug_G Lead Moderator

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    The pack heater is variable power, but it can draw as much as 6 kW. The cabin heat can also draw a similar amount of power. But this only happens when you first start up a cold soaked car.

    Tesla doesn't tell us the actual battery temperatures, but if you cold soak the car below freezing the battery will be heated when you initially power up. You can avoid most of that by preheating the car (using the remote App) while the car is plugged into a charging station. It will draw AC power to heat the pack. This will have a huge benefit in preserving range.

    Once you are underway, waste heat from the battery and drive train provides most of the heating. I believe the waste heat is also used via a heat pump to warm the cabin (it uses a resistive heater when the drive train is cold). So once the car is at equilibrium it's actually very efficient in terms of heat usage, even in pretty extreme cold.

    At that point the loss of range is mostly due to aerodynamic effects (cold air is denser) and some rolling resistance (rubber gets harder). I've driven 303 km (190 miles) at -20C (-4F) in a blizzard and arrived with a decent safety margin (speeds around 50-55 mph mainly due to the road conditions) - while keeping the cabin toasty.

    At a few degrees above freezing there is little if any impact on range. Certainly at +5C (41F) there appears to be no impact. As you drop through 0C (32F) you start to see some loss of range, perhaps 10%. As the temperatures drop further the loses increase to about 20%.

    Somewhere around -25C or so (-13F) it appears the pack heater starts to run continuously, even at highway speeds. At that point you have more substantial range impacts, perhaps as much as 30%.
     
  3. neroden

    neroden Happy Model S Owner

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    You're thinking about temperature, but it isn't the biggest issue. Neither are hills.

    Don't forget the friction from snow/slush/ice accumulating in the wheel wells. With some types of snow you'll have no accumulations; with others, you'll have constant accumulation.

    On my trip to Michigan this was the *dominant effect* on my range. I was recording 600 Wh/mile for sustained periods.

    By contrast, dry roads and clean wheelwells in bitter cold? Not a problem.

    I also had terrible mileage in a really bad rainstorm at slightly-above-freezing temperatures. Haven't quite figured that one out.
     
  4. Doug_G

    Doug_G Lead Moderator

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    If the car is constantly pushing through standing water it requires a lot more power to keep moving. This only matters in really heavy rain; if the road is merely wet it's no big deal.
     
  5. jerry33

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

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    Water on the road adds a lot of rolling resistance and the water splashing up from the tires probably cools the battery.
     
  6. kcveins

    kcveins delivery 2/7

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    Speed really will kill you in the cold.
    I have found during this very cold winter that -10F to -15F with only a little snow on the roads, going at 70 mph will really limit you to about 125 miles; going 55mph allows you a range closer to 165 miles.
     
  7. David99

    David99 Active Member

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    That's great info. Living in Los Angeles, I had very little experience with driving in cold weather and the effect on range. I looked at Tesla's range calculator and it shows the temperature doesn't affect range a lot up to 0 degree. And the effect is definitely not just from the battery being cold. Air density and other resistances count in. I think that's why Tesla doesn't bother heating the battery much up to that point. Many here asked for a switch to preheat the battery, but I guess from an actual range point of view, it would not make much of a difference and and waste a lot of energy.
     
  8. jerry33

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

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    That would be true for long trips. For short trips, meaning at least up to 25 miles, it makes a great deal of difference. Tesla's range calculator is based on long trips (50-150 miles) as range isn't an issue for short trips.
     
  9. ElectricTundra

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    For short trips around town I've noticed a considerable difference with only cold weather as we've not really had any snow until yesterday. During the summer I was averaging about 315 wh/m and in recent weeks with weather in the 20's F I'm consistently over 400. This is mostly lots of 2-15 mile trips with pre-heating in my garage with HPWC.

    Glad to hear that longer journey's should be more more efficient.
     

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