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Happy with Efficiency on Latest Trip (but with a small mystery)

Discussion in 'Model S: Battery & Charging' started by David29, Jun 9, 2017.

  1. David29

    David29 Active Member

    Joined:
    Aug 1, 2015
    Messages:
    1,029
    Location:
    DEDHAM, MA
    My spouse and I made a trip from the Boston area to Philly and back last weekend for a wedding. We drove down on Thursday and back on Sunday. Thursday (June 1) was a lovely day, sunny, blue skies, temps in the low to mid 70s. Sunday started out overcast in Philly, a bit more humid, and gradually turned rainy as we drove north and as the day passed, ending in a steady rain through CT to home, with temps falling into the high 50s.

    On the way down, we were able to maintain good highway speeds except in and around the metro NYC area. Midway through our trip, we changed plans and decided to take the Tappan Zee Bridge to avoid what Google maps indicated was serious delays on !-95 approaching Manhattan. Once on the NJ side of the Hudson, speeds picked up again, so we were able to travel at 60 to 75 mph most of the way, and even 80 for awhile on the NJ Turnpike. (Love that nice, new, smooth cars-only section of the NJ Turnpike!)

    On the way back, traffic was much worse on the trip towards Manhattan. We followed the car's nav system (and checked Google maps, too), which had us use the George Washington Bridge. That turned out to take forever. And then rain on the CT and MA legs slowed us somewhat. So our return speeds were somewhat lower than on the route south.

    Interestingly enough, our average energy consumed per mile was nearly identical on the two legs of the trip -- 295.5 Wh/mi southbound, and 292.8 Wh/mi northbound, for an overall average of 294.2. The distance was 338 miles southbound and 327 northbound, total of 665.5 miles.

    I felt pretty good about this. The EPA rated range for my 70D is 240 miles, which translates to 292 Wh/mi, so we were very close to that. I think we were able to come so close because of moderate temperatures, so minimal energy was used for AC or heating. (We ran with the climate control on Auto for the entire trip.) The southbound trip was a tad less efficient, likely because of slightly higher average speeds and possibly a bit more AC load. But I was pleasantly surprised that rain did not have seem to have much effect on the return trip, as that supposedly adds to energy consumption.

    The one thing that puzzles me is that we seemed to "lose"some energy someplace. My numbers above are from using the trip gauge (Trip B) to track the mileage and energy use for the trip. I also tried to record the energy added at Supercharger stops. Unless I made a recording error (which is entirely possible), we added 180 kWh at our 5 Supercharger stops, and used about 40 kWh from the battery, for a total of about 220 kWh. But the trip data shows we used only 196 kWh. So I cannot account for about 24 kWh. I know there are some losses in the AC to DC conversion when I use an AC charger, but I did not think there were much if any such losses when charging from a Supercharger. it could be that we lost a little when preheating, but I do not remember doing that much at all because of the mild weather. So I wonder where that 24 kWh went....

    I guess I will need to be more careful about my record-keeping next time!
     
  2. Rocky_H

    Rocky_H Active Member

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    Location:
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    If you are looking at the trip gauges for energy use for any amount of driving that is greater than one continuous drive, there will be energy that appears "missing" or "lost" from there. The trip gauge only measures energy used while in Drive. So any form of after the fact battery management, climate control, etc. is technically used, so some rated miles will disappear from that, but it will never show in the trip meter. Also, yes, I think there is some 10-15%ish efficiency loss in charging conversion perhaps.
     
    • Informative x 1
  3. KidDoc

    KidDoc Supporting Member

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    Aug 6, 2014
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    Location:
    College Station, TX
    That doesn't account for 24 kwh though. 24 kwh is a good bit of juice, nearly 100 miles worth at 290 wh/mile. I have no idea where it went but I'm interested in people smarter than me answering this question. Very odd.
     
    • Like x 1
  4. thefortunes

    thefortunes Member

    Joined:
    Jun 14, 2013
    Messages:
    625
    Location:
    Wisconsin
    My SuC efficiencies (per TeslaFi) range from a low of 78% for a quick 10 minute/16 kWh/55 mile charge to a high of 98% for a 1 hour/55 kWh/186 mile charge.
     
    • Informative x 1

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