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Energy "since last charge" vs "energy consumption"

Discussion in 'Model S: Battery & Charging' started by tomp, Apr 8, 2014.

  1. tomp

    tomp Member

    Joined:
    Dec 3, 2013
    Messages:
    417
    Location:
    Durham, NC
    Hi,
    I've noted that the energy "since last charge" does not usually match the average "energy consumption" (over the latest 5/15/30 miles). It appears to me that energy "since last charge" is usually greater (on a Wh/mi basis) than my average consumption. In my case this comparison is easy because my daily commute is almost exactly 30 miles, and I charge every day at work.

    Is this because energy "since last charge" is counting energy used while the car is off?

    As a follow-up, for lifetime Wh/mi (i.e. as displayed on the Trip Meter), does this include energy utilized while the car is off/parked?

    Thanks!
     
  2. tezco

    tezco Sig P85

    Joined:
    Nov 9, 2012
    Messages:
    820
    Location:
    Colorado
    I don't think the idle power losses are tracked. Before sleep mode the car used a lot of energy and I don't remember seeing huge figures in the display.
     
  3. mknox

    mknox Well-Known Member

    Joined:
    Aug 7, 2012
    Messages:
    9,568
    Location:
    Toronto, ON
    I have noticed the same thing for some time now (over several firmware releases). My commute is about 40 miles each way, and in the morning I always note that when the "Since Last Charge" screen shows exactly 30.0 miles, the Wh/mi number is always higher than the Wh/mi number on the graph set to show the average for the last 30 miles. I figured they should be exactly the same at the 30.0 mile point in the trip.

    As far as the lifetime Wh/mi question: no, it does not account for charging or standby losses.
     
  4. dhrivnak

    dhrivnak Active Member

    Joined:
    Jan 8, 2011
    Messages:
    3,018
    Location:
    NE Tennessee
    I think the watts/mile is calculated while driving and so the "vampire" drain and charging losses are not counted. But when measured from the wall, changing losses and vampire drain is included. I expect the wall, or in my book the real number, to be a good 15% higher than the driving watts/mile.
     
  5. scaesare

    scaesare Well-Known Member

    Joined:
    Mar 14, 2013
    Messages:
    6,164
    Location:
    NoVA
    Indeed... there is often discrepancy between the two numbers... this begins with pulling out of the grage and the "Since Last Charge " number has spiked up to 600-1200+ wH/mi (reflecting various subsystem energy consumption as the car starts up), without a corresponding spike in the energy graph (which would be difficult, as that energy is consumed with 0 miles driven).

    I typically find the two numbers do match pretty closely after 30 miles... particularly under ideal conditions (warm weather, mild driving habits, etc...).

    I tried to get a handle on some of the various display reporting a bit back... and there was some good discussion. Some behavior has changed with newer firmware, but it might be good reading if you are interested: Energy Accounting
     

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