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I know it's not a perpetual motion machine, but...

Discussion in 'Model S: Battery & Charging' started by Barry, Apr 23, 2015.

  1. Barry

    Barry Member

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    I drive a lot in the mountains. One thing I've noticed in my short ownership experience is the car seems to gain more range over extended downhills than it loses on the same hills, going uphill.

    For example, yesterday I drove from home near Denver to Arapahoe Basin ski area (great ski day, BTW), going from 5500 to 11000 ft ASL. I used about 100 miles of range for the 70 mile drive uphill. Coming home, I used about 30 miles of range going downhill, for a net gain of 10 miles. I've noticed similar effects on another drive I regularly do with about a 3000 ft elevation change.

    Is this simply an artifact of the range calculations? If not, how is this possible.
     
  2. cantdecide

    cantdecide Member

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    Basically what you are saying is that you use 130 miles of range to go 140 miles. Is your average speed under 65mph?
     
  3. gavine

    gavine Petrol Head turned EV Enthusiast

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    I think it has to do with the calculations. When going uphill your Wh/mile is high so the range estimate is affected negatively. On the way down, the Wh/mile increases so much, that the computer adds range based on the current efficiency. You're not actually gaining more miles than you lost,unless your end point is at a lower elevation than your start point.
     
  4. CmdrThor

    CmdrThor Member

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    Driving on a flat surface is always going to be more efficient than going up/downhill and ending up at the same elevation. This is because regen is not 100% efficient among other things. The "gain" you are seeing is a result of you driving slower than the range calculation originally predicted.
     
  5. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    As cantdecide says, it's just that you were operating under the expected rated-mile energy curve. I'm guessing you weren't a speed demon? There are other variables as well, such as wind, temperature, etc., that may make comparing the trips difficult.

    Very early on, there were a couple of people here who attempted some regen efficiency calculations and came up with a number somewhere around 85%, all else equal. So it's not because it's more efficient at regen than powering the car. :)
     
  6. lphe

    lphe Member

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    In general, you will get better mileage driving on level roads vs. driving on hills. To go up the hill you need to convert electrical energy from the battery to potental energy required to climb the hill. This conversion is not 100% efficient--it is perhaps 85% efficient. However, you get all the potential energy back when you come down the hill. The net effect is that you use 15% of the potential energy required to climb the hill more energy driving up and down the hill vs. driving on a level road.
     
  7. Barry

    Barry Member

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    No. Most of the drive was on I-70 and I had TACC set for 70 mph in both directions.
     
  8. cantdecide

    cantdecide Member

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    Generally high altitude means lower air density... Which improves efficiency... But this is typically offset by cold weather on shorter trips. If it wasn't that cold, and particularly if you were more coasting down hills than regenning then 70mph and these figures can be consistent.
     
  9. Barry

    Barry Member

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    On the way up, it was about 50 F at the start and 40 F at the top. On the way home, it was 48 F at the top and 68 F at the bottom.
     
  10. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    The car experiences a pretty major boost in efficiency at higher temps. Threshold for me has been around 55-60 degrees.
     
  11. cantdecide

    cantdecide Member

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    50 is probably pretty ideal... Some suspect that was the primary explanation.... Altitude helped and you didn't kill the efficiency through cold battery or car heating or driving way too fast. Having a bit of regen and reusing it was a relatively small loss.
     
  12. jerry33

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

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    It also helps if you go a bit slower uphill and a bit faster downhill.
     
  13. David_Cary

    David_Cary Member

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    Higher temps always help so ideal is the highest temp you can do without a/c. I suppose with a small amount of a/c (and of course battery/motor cooling) you can still do better if it is hotter - ie running the a/c set to 80 at night when the outside temp is 90. That might be better than 80 degrees with no a/c - if you are going really fast. Air density matters proportionally more as you go faster.
     

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