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Hypermiling in the Cold

Discussion in 'Model S: Driving Dynamics' started by Doug_G, Feb 2, 2013.

  1. Doug_G

    Doug_G Lead Moderator

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    On long trips, I've been getting about 70% of ideal range, or equivalently 80% of rated range, in very cold conditions (e.g. -15C to -20C), with the heat operating in Range Mode. At 80 kph (50 mph) I can drive around 330 km (205 mi) on a full Range charge, without freezing!

    Cabin heat appears to draw 5-6 kW at full power (hard to tell exactly from the power gauge). The pack heater draws about the same amount at full power (it does ramp up/down as needed).

    I've been using a spreadsheet derived from the above, plus the numbers on Tesla's web site (from their range calculator and adding data from their rough graph) to calculate range and power draw under various conditions. Here are some observations, based on driving 80-90 kph (50-55 mph) in the cold:

    Reducing your speed by 1 kph gives you about 5 km of extra range. Or equivalently 1 mph gives you 5 miles of extra range.

    Saving 1 kW power will get you about 16 km (10 miles) more range.

    Going from full cabin heat to no heat will give you 68 km (43 miles) more range. (Note: ballpark only - very sensitive to conditions) This is equivalent to slowing down by 5 mph.

    Typical HID headlights use about 35 watts each, so turning your headlights on probably pulls about 70 watts. Doing that reduces your range by about 1 km (0.6 miles). So don't panic if the sun goes down. The cold matters, not the light.

    Seat heaters likely draw a similar amount to the headlights. Use them liberally.

    Dimming the display might save you 15 watts (guesstimate). That will get you 300 meters (1000 feet). Not worth bothering with this sort of thing.

    Charging your phone will consume at most 2.5 watts (USB power limit). That will consume 100 meters of range (300 feet). Go ahead and charge your phone - you might need it!

    In short don't sweat the small stuff. If you vigorously use all the electronics in the car you might knock a mile off your range. You can make up for that by slowing down by a mere 0.2 mph.

    Full power on the pack heater and full cabin heat could reduce your range by 80 km (50 miles) if they were running full blast all the time. Fortunately the pack heater ramps down after 20 minutes or so, and you can't run the cabin heat at full power for long without breaking into a sweat. Still, it's a good idea to leave on a long trip with a toasty pack and cabin. About 20 minutes before your charge is due to finish, turn on your cabin heater. Once the charge is complete leave immediately, while the pack and cabin are toasty.

    The single most important thing you can do to extend range is to slow down. However, when there is extra power draw the optimum speed is higher. That's because a fixed power draw like a heater consumes more pack capacity the longer it is running. If you're going slower, it's running for a longer time. The sweet spot in cold temperatures is probably 60 to 70 kph (40 to 45 mph).

    Instead of turning the heat off altogether, turn on Range Mode to limit the cabin heat power. Then drive 5 kph (3 mph) slower to make up for the power usage. You'll be a lot more comfortable!
     
  2. Chgd Up

    Chgd Up Sig 1004

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    #2 Chgd Up, Feb 2, 2013
    Last edited: Feb 2, 2013
    Doug, I also have done some low temperature mileage runs, and wanted to loose the 50 wh/mile cabin heating penalty. As you noted the battery heats it self as you drive after a while.

    I looked at the Tesla blanket but ended up buying a 12v heated one. The only trick is managing fogging and the Aquapel anti fog worked for me, it is a little touchy to apply without streaks but works.
     
  3. Alpha

    Alpha Member

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    Good stuff. Thanks for posting. I live in an area that usually doesn't get nearly that cold, but I am still very interested.
    Would be really interesting to here the "heat" side of it too (how much it's affected in a super hot environment, with pack cooling and lots of cabin AC, etc.)
     
  4. Doug_G

    Doug_G Lead Moderator

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    Fortunately air conditioning doesn't take nearly as much power as heating does. In my Roadster I'm not sure if I could empirically tell the difference between A/C on low and A/C off - other variables were larger. Not tried it yet in the Model S, obviously...
     
  5. ebbrey

    ebbrey Member

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    Thank you Doug_G for these numbers!
    I've been looking at my own spreadsheet while waiting, and i wonder since this is based on 80km/h.. and it gives you 330km on range mode (300 standard). what if..
    i have a 300km drive planned. The speed limit which i would like to drive in for 200 km of the route is 100 km/h, after 200km last 100 km is with 80 km/h speed limits. How much range would you say i would have lost in the first 200 km?
     
  6. Doug_G

    Doug_G Lead Moderator

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    I really couldn't recommend you do that. I did a 300-odd kilometer trip, with Range Mode heating, and arrived with a safety margin of around 30 km. What you're proposing would have you arriving with NO safety margin. You might not make it.

    Maybe if you drove with the heat entirely switched off (except for seat heaters) you could do it. Of course you'd probably have to defog once in a while.

    Personally, I would drive no more than 85 kph if you want to use Range Mode heating. Regardless I'd keep a close eye on your Projected Range in the Energy App, and compare against the GPS distance-to-go. If it's not looking like you'll arrive with some margin, then you need to slow down. It doesn't help that the faster speed limit is the first 2/3 of the route - the sooner you start managing your range the more wiggle room you will have.
     
  7. Dr.Ling

    Dr.Ling Member

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    Great info for us living way up north!
    I'm picking up my car next month and I want to really stretch it the very first day: Go 385 km before charging, in about -5 deg C. Could I possibly make it if I average 70 kmh?

    According to JurassicTest my route has a few elevation changes as well, and I've calculated that those will cost me about 30km in range...... :(
     
  8. mknox

    mknox Well-Known Member

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    I've noticed a couple of things in the cold with the car's heater:

    Switching the HVAC to Range Mode does immediately make the power meter drop a bit. Jumps back up when you switch back to "Normal" mode.

    Switching to "Max" front defrost seems to override Range Mode as the Power Meter jumps up to "Normal" mode heating levels.

    Turning the HVAC completely "Off" while not moving or parked drops the power meter to essentially zero, even with a cold battery pack as evident by the regen limit indicator. Question: Is pack heating represented on the dash Power Meter and/or is pack heating disabled when the HVAC is off?
     
  9. Doug_G

    Doug_G Lead Moderator

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    Pack heating is indeed represented on the power meter. I don't believe the pack heater runs if you're parked, unless you preheat using the remote app. Or if you are charging.
     
  10. neroden

    neroden Happy Model S Owner

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    Hmm. Your range estimates are just a tad lower than my worst-case estimates and tell me that if the weather is really cold I may need one small top-up between Ithaca, NY and Niagara Falls, Ontario in January. Will plan route accordingly. :)
     
  11. Doug_G

    Doug_G Lead Moderator

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    That is a good idea, especially in extreme temperatures e.g. below -30C.
     
  12. mknox

    mknox Well-Known Member

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    That must be it. I was sitting in the car, with the car "on" but in Park while "eyeballing" the power meter. I'll have to try turning the HVAC off at a red light or something and observe if I can "see" the pack heater draw.
     

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