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Phoenix to Flagstaff and back - an elevating experience

Discussion in 'Model S: Driving Dynamics' started by kishdude, Jan 29, 2013.

  1. kishdude

    kishdude P #130

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    Glendale AZ
    I did my first out of town road trip today. It was a one day turn-around trip from Arrowhead (northern Phoenix) to Flagstaff AZ. This is not a typical road trip for the Model S in that in the 125 miles in the trip there about 5000 feet of elevation change as you go up I-17 to Flagstaff. The plan was to travel to Flagstaff to a second home we own there, do a few hours of work there and then drive back to Phoenix. Near the end of the summer, my son and I had installed a NEMA 14-50 outlet in our garage in Flagstaff and this would be my first time testing it out.

    I started off at 745AM with a range-mode charge on my P85. The temperature in Phoenix in the morning was about 40 and by the time I got to Flagstaff, it was 15. I didn't use any range mode setting and had the cruise control set for 78 - definitely was not trying to save any energy. The car performed flawlessly. The roads by the time I got to Flagstaff were slushy, but I had no traction problems even with the 21 inch wheels. I was defintely blowing through the electrons though. By the time I reached Flagstaff, I had driven 127.4 miles and used a total of 61.3 kWh for an average of 481 Wh/mi and had 31 miles projected range left. At this point, I couldn't really tell if this increased rate of consumption was mainly due to the cold, the speed, or the elevation change. I immediately plugged in to the 14-50 which thankfully worked without a hitch. I was getting 240v at 40a but the maximum rate of charge I got to was 18 mph.

    After getting some work done and charging for 6 hours at which time I had 225 miles rated range, I started back on the return trip to Phoenix. The weather was about 10 degrees warmer than the morning, I set the cruise control on the same 78 as on the way up. The return was a huge difference in energy usage despite going at the same speed and not much of a difference in temperature. On the return, I used only 37.2 kWh (vs 61.3) and had an average of 293 Wh/mi. This is about a 40% drop in energy consumption which at this point can only be due to the elevation change. This elevation change of about a mile in height over 125 miles in length works out to slightly less than a 1% grade on average the whole way.

    So the take away is that changes in elevation have a huge impact on range which seems obvious, but I did't think it would be so dramatic. In an ICE car, you would certainly use less gas going downhill instead of uphill, but I don't think that you would see a 40% drop in gas usage. This is because of inefficiency of the ICE, 60% of the energy is going to be lost anyway and uphill/downhill only affects the remaining 40%.

    For those in Phoenix wanting to take this trip, please remember that I started from Arrowhead and even with the increased consumption on the way up, I didn't have any range difficulty with an 85 kW battery. If you are leaving from Chandler or Mesa, I think you would be cutting it close. As far as trying it with a 60 kW battery, it is probably possible if driving at slower speeds and leaving from northern Phoenix. But remember, I only had one passenger in the car and if you have more, your range will be less.

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    On the way up - just after Camp Verde. The big regen area you see is on the hill going down to the Verde Valley - regen the whole way down.

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    Some slush and ice on the road in Flagstaff.

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    Energy usage to Flagstaff

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    Charging up in Flagstaff

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    On the drive back. One of the rare places in the US you can have the cruise control set for 78 and still be using 158 Wh/mi over a 30 mile range.

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    Energy usage back to Phoenix

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    Dirty but home.
     
  2. stevezzzz

    stevezzzz R;SigS;P85D;SigX

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    Hey, knish dude, thanks for the writeup. It's good to have real-world experiences like yours in mountainous terrain to draw from.

    A couple of observations:

    1. You had 31 miles Projected remaining, but your Rated miles remaining must have been more like 50. Did you happen to notice?

    2. When driving in hilly terrain it's not just the overall elevation gain that will kill your range, but the total elevation gain of all climbs. That's because climbing 1000' costs you about 7 rated miles of range, while descending 1000' gets you only about 4 miles of range back through regen, best case. You had at least one long descent in the middle of your climb to Flagstaff, so your total climbing could easily have been twice the overall elevation gain of 5000'. If it was actually 2x, then the extra range you consumed only due to climbing would be 5x7 + 5x(7-4) = 50 rated miles.

    Factor in losses due to slush and cold temperatures on the way up, and your 61.3 kWh begins to seem pretty reasonable.

    BTW, love the Dolphin Gray!
     
  3. aviators99

    aviators99 Model S - R140

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    My calculations agree. Based on his 61.3 kWh shown at the end of the leg and my understanding of how rated range is calculated, it should be 48.69 rated.
     
  4. mnx

    mnx 2013 P85

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    His Model S is brown (see the pic inside the garage) :) But it does look grey in the last picture!

     
  5. stevezzzz

    stevezzzz R;SigS;P85D;SigX

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    #5 stevezzzz, Jan 30, 2013
    Last edited: Jan 30, 2013
    :redface: Chagrined: the auto white balance had me going. Hey, the brown is very nice, too.

    Pardon me for going OT, but this is the second time in recent weeks I've mistakenly thought a car was gray. After picking up a rental at the airport the other evening I went back to the terminal to get Marcia, who'd stayed behind to pull the suitcases off the baggage belt. Sent her a text msg to look out for me in a gray Mazda; when I found her she was wearing a puzzled expression and said, "This car is red!" I turned around and looked and sure enough, it was bright red. I'd viewed the exterior under the sodium vapor lights at the rental lot and would have sworn under oath that it was gray.

    BTW, it's no fun leaving an S at home and driving a rental ICE for a week.
     
  6. MarkR

    MarkR Member

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    Kishdude: Great post. Great pix. Thanks for giving us some real world experience with the S.
     
  7. Doug_G

    Doug_G Lead Moderator

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    Of course this is also worst case, in that a gradual downhill won't push you into full regen, so a good chunk of the energy gained will be going into moving the car forward, which will have no additional losses. It really depends on the altitude profile of the trip.
     
  8. jomo25

    jomo25 P4398

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    Great info Kish! Jives essentially with calculations my friend who owns a Roadster. I asked him this exact question. I wanted to know if the 60 would be sufficient to make it to Flagstaff on a single charge. based on his experience, and the range curves that Tesla has posted, he thought it would be close at 65 mph up to Flagstaff. But obviously not an issue back down. He estimated an 10.9 kWh hit for the elevation change from 1200 ft to 7000. the calculation is 1.9 kWh per 1000 feet elevation change for a 5000 lb vehicle. (and its linear as the weight changes). So, in a perfect world, you'd expect about a 22 kWh spread between your outbound and return trips.

    Your spread was 24 kWhr for roughly 5000 lbs. so, its close. other real world factors probably account for the difference (temp differences, the climb/descent aren't 100% in one direction, so there's some regen loss).

    The 60 is about 200 lbs lighter, I believe, based on Tesla's words in another post, so that helps. But I left with the conclusion that the 60 could go to FLagstaff, Sedona, Tucson in a single charge if I had to. Worst case, I'd stop up near Arrowhead (or even Anthem) on my trip from Tempe and get a top off charge while I ate something to give me the extra range. But being able to roadtrip to those places bolstered my decision to go with a 60.

    That is assuming I can actually order one (see my HOA saga in the AZ Group thread).

    Thanks again for the data (and pics). The confirmation is definitely valuable!
     
  9. stevezzzz

    stevezzzz R;SigS;P85D;SigX

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    That's what I was alluding to. And at 78mph it has to be a pretty good downhill grade to get much regen at all: aero drag is a bear. Just like you increase range on the flat by selecting a lower speed, you can also improve your regen on any downhills by slowing down: even slowing to 50 makes a huge difference. If the downhill isn't too steep, you'll do even better if you avoid regen entirely, coasting with the ammeter pegged on zero. You don't want to be coasting too fast (aero drag, again, not to mention safety and speeding tickets). But I don't know where the sweet spot lies...anyone?

    On a broader topic, has anyone done the math to show how to minimize the time required to get to your day's ultimate destination when a trip involves charging stops? You'll want to drive slower when the next charger is a 30amp than when it's a 70amp, etc. It'll depend on a whole host of factors, including the charging rate at intermediate stops, elevation profiles, road conditions, wind speed and direction, temperature, etc. There's got to be a market for a really good EV trip planner app.
     
  10. mnx

    mnx 2013 P85

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    I've read on here, that it's complicated but you want to drive at the rate at which the charger replenishes your miles.

    eg. a 14-50 at a campground is ~30mph, HPWC 60mph, 30A J1772 18mph or Tesla Supercharger as fast as you dare.

     

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