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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

    Dec 3, 2013
    Durham, NC
    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?

  2. tezco

    tezco Sig P85

    Nov 9, 2012
    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

    Aug 7, 2012
    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

    Jan 8, 2011
    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 Active Member

    Mar 14, 2013
    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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