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High Consumption 500+ Wh/mi in the 1st 5-10 minutes of trips

Discussion in 'Model S: Battery & Charging' started by simplesolid, Jan 5, 2017.

  1. simplesolid

    simplesolid Model S 60 AP2 Glass Roof

    Joined:
    Nov 12, 2016
    Messages:
    70
    Location:
    Florida
    Whenever I ride my car, my consumption is very highin the first few minutes then it gradually drops. Let me also say that I live in Florida and the weather has been about 87 degrees.

    When I start my trips my consumption is around 450-800 wh/mi usually for 5 to 10 minutes then it drops and eventually gets to below 300. My car has 950 miles on it. But I am trying to figure out why it is so high at first, is it because the battery is heating up even tho is 87 degrees outside?

    One of my latest 31miles trip average of 268 Wh/mi, how it was above 500 in the 1st 5-10 minutes.

    My Lifetime average right now is 313 wh/mi.

    Is this normal behavior?

    Thanks
     
  2. swaltner

    swaltner Member

    Joined:
    Oct 13, 2012
    Messages:
    665
    Location:
    Kansas, USA
    Yes, this is totally normal, assuming you run the air conditioner. The power draw from the HVAC system spikes on initial power up to try to get the cabin at your desired set point. Once the cabin temp has stabilized at the set point, it can lower the power demands dramatically since it just needs to cool/heat for the temperature losses from the cabin to the outside world.

    I don't know the exact numbers from a Model S, but on the Leaf, driving at 55 mph takes something like 15 kW. That works out to 272 Wh/mi for the traction motor. The air conditioner initially consumes 3 kW, eventually dropping to something like 500 W. At 3 kW, that would bump the total power draw to 18 kW and the efficiency to 327 Wh/mi. If you are initially driving on surface streets or in some other stop and go traffic, the AC consumption continues, even when you're not moving, driving the *per mile* consumption WAY up. An extreme example of this coming into play would be that you are stuck in a traffic jam for 1 hour with the AC blasting away drawing 3 kW of power the whole time. In this one hour of time, you only move a single mile. Drawing 3kW for one hour means you would burn 3 kWh of energy plus the small amount of energy it took to creep along at 1 mph. This would yield a consumption on the dash of over 3,000 Wh/mile.

    Next time you get in the car, simply turn off the air conditioner and you should see fairly consistent energy usage numbers.

    In other words, just ignore the Wh/mile reading when you first get into the car. This reading is going to be all over the map when the car first starts up, primarily because there are some heavy power draws when the car first starts (bring cabin to desired temperature, potentially warm the battery if it's been sitting in the cold, etc...). There have been reports here where people thought maintenance techs took their car for a joyride because of VERY high per-mile power draws. These ended up just being times when the car was "idling" in the garage. It was burning power sitting on a car lift, yielding impossibly high per-mile consumption readings.
     
    • Informative x 1
  3. JRMW

    JRMW Member

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    Nov 13, 2016
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    Location:
    Minneapolis
    Do you run your AC when you get into the car?

    My guess is that this is the energy consumed to initially cool your car and battery.

    Here in MN my car consumes 750 wh/mile the first 5 to 10 minutes, up to 1100 if I use the heater!
    Then it drifts down to 350 or so
     
  4. Vger

    Vger Active Member

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    Yes normal. This was also the source of a bug in the earlier versions of the energy prediction function when travelling. When leaving a Supercharger, it used to want to send you right back to the same Supercharger because of overestimating your future energy consumption during this early period of high per-mile/km usage. Thankfully, they fixed this (I think it was 7.1).
     
  5. Electric Joe

    Electric Joe Member

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    Howell, MI
    I've noticed this too, even when the weather is mild and I'm not using heating or cooling. I always assumed it was for the same reason my Prius used to show terrible efficiency (for a Prius, anyway) of about 20 MPG for the first few minutes of driving if I reset the gauge. It takes a lot of energy to move a car from a dead stop. A test would be to turn on the car and very, very slowly accelerate without running the climate system. Maybe then the wh/mile measure would be reasonably low right from the start.
     
  6. idealsol

    idealsol Member

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    So I'm wondering, do you actually save energy by initially turning off a/c, or do you just disperse that usage more evenly
     
  7. ecarfan

    ecarfan Well-Known Member

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    Normal.

    Tell us your wH/mi after driving 30 miles at around 70mph at 80 degrees air temp with no headwind on a level road (is there any other kind in Florida? ;). Should be 310-320, I would estimate.
     
  8. sorka

    sorka Active Member

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    • Energy just to get the car moving. i.e. if you coasted to a stop from 50 MPH just after starting out, you'd see your that wh / mile average plummet. i.e. compare it after x time from 0 mph to 0 mph, not 0 mph to 65 mph on the freeway.
    • Using climate control in the beginning will draw a lot more power to get the cabin to setpoint.
    • The viscosity of the drive unit fluid is far FAR higher when cold and will take a while to warm up. It will take more energy for the gears to move through it until it does.
    That last one is a bigger factor that people realize. If you leave climate control off and simply drive the car for a few miles and return home and then leave again soon on another trip, your wh / mile will be a lot lower with the drive units already warm.
     

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