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Rated range during trip dropped faster than expected for averaging 223Wh/mi

Discussion in 'Model S: Driving Dynamics' started by yobigd20, Jul 17, 2015.

  1. yobigd20

    yobigd20 Well-Known Member

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    After a brand new drive unit install yesterday (not remanufactured), new battery contactors, and an update to v .251, I am concerned that something may be wrong with energy usage or range calculations. I have a 190 mile round trip today (no dest charger) so I only charged to 90%. I decided just to "drive slow". Previously on long trips I observed that if you drive slower, the rated range doesn't drop as fast (common sense if your going 250Wh/mi vs 350Wh/mi).

    I'm at my destination halfway and the rated range seemed to drop much faster than they should have given how slow I was driving and how little energy I used.

    Rated range at start: 222
    Rated range after 94.6 miles: 130

    7584b4bde8c78cc7bc9c420c8bd11401.jpg

    Display:
    Total energy used: 21.1kWh
    Avg energy: 223Wh/mi

    Now the problem for me is that those numbers do not make sense. They do not look accurate. By my calculations, since I drove so conservatively and used little kWh, my range should have only dropped by about 70 miles. Instead it dropped by 92.

    AFAIK Tesla's rated range calculation is done assuming about 300Wh/mi. Since I only went 223Wh/mi, that means I saved about 77Wh/mi by driving conservatively. Over 94.6 miles that is 7284Wh of savings. Using 300Wh/mi , that means I should have saved about 24.2 miles, effectively meaning that rated range should have only dropped by about 70.3 miles. Instead it dropped by 92 miles. IMO that's a pretty significant error difference.

    You can do this calculation several ways. I'll do it another way. If I only used 21.1kW, at the rated range calculation of 300Wh/mi, it should have only dropped 70.33 miles, not 92 miles.

    Again, assuming Tesla's rated range calculation uses 300Wh/mi, common sense says if I drove 94.6 miles at an average of 300Wh/mile the rated range should drop by about 94.6 miles (duh). It dropped by 92 miles. Very close. However , 223Wh/mi is a significant difference from 300Wh/mi. About a 25.6% difference. I should have got about 74.3% of what 300Wh/mo would have got. The difference between 92 and 94.6 is not 25.6%. Guess what 74.3% of 94.6 is? 70.3.

    Am I calculating this wrong or does something look off to you all too?
     
  2. kennybobby

    kennybobby Member

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    It looks like the slower driving will get you home okay. The range estimator started at 222 and you drove 95, so you would have 127 left. But your good driving caused the range estimator to say you have a few more miles available, 130.

    It seems that if the estimated and the actual are really close then that would be a good thing?
     
  3. sorka

    sorka Active Member

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    It would be more helpful to know what percent your started at and ended at. That won't change based on how you drive.

    i.e you should have used 27.8% of your battery. If it showed a lot more than that, I'd be worried.
     
  4. yobigd20

    yobigd20 Well-Known Member

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    Right, I "gained" like 3 miles. But driving that slow and getting 223Wh/mi should have allowed me to "gain back" much more like 20 miles. (I say "gain back" but it's more like "used less").

    And FWIW the question here is the range calculation. I'm not worried about not making it back as I know I can (also I can go to a supercharger out of my route if I really felt like it ).
     
  5. 3mp_kwh

    3mp_kwh Member

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    It would be a good thing, if Tesla's 'rated range' values didn't more resemble an SOC %. He's losing about 1, for 1, at a very low 223Wh/mi. I wonder if two different sensors are involved. Perhaps one aft of the new motor unit, and one before it possibly reporting some artificially low wh/mi, as it gets broken in? Just speculating.
     
  6. yobigd20

    yobigd20 Well-Known Member

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    I started at 90%. I'll check the % when I get back to the car but the slider looks like it's at 50%. Aka it thinks it used 40%. That's why it all looks wrong. I'll confirm this later today.
     
  7. yobigd20

    yobigd20 Well-Known Member

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    This. ^^^^ This is what I mean I'm worried about. It should NOT have been 1:1 for only going 223Wh/mi
     
  8. David99

    David99 Active Member

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    The car doesn't add in any usage when the car is not moving. Every time you stop at a red light or a bathroom, the car uses energy that isn't added into the trip meter. That could account for some differences.
    The rated range display is not always consistent. I often see it jump up or down while parked or while driving. Mostly it subtracts miles about equal to how many I actually drive, but sometimes I drive for 5 miles and the rated miles stay the same. Or the opposite, I drive two miles and it drops 5 in an instant.
     
  9. hiroshiy

    hiroshiy Active Member

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    Did you turn off range mode during your drive?

    Also, you might have stopped at a cool location and if the AC setting was a bit higher than ambient, the heater could have kicked in.
     
  10. yobigd20

    yobigd20 Well-Known Member

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    No (range mode meaning reduced AC/heater). I always leave that on.
     
  11. hiroshiy

    hiroshiy Active Member

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    I asked because range mode off gives you smaller rated range at the time of switching off. But you apparently kept that on so my guess was wrong :)
     
  12. yobigd20

    yobigd20 Well-Known Member

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    So I did the same exact run today from the original 1st post. This time I started with a 90% charge of 220 rated miles, and ended with 145 miles rated range while getting an almost exact same Wh/mi and distance (the .3 mile difference in distance was because in the OP I stopped to go wee wee and this time I didn't haha). But wow what a difference! In the op, rated range dropped 92 miles for 223Wh/mi, but in this trip it dropped 75 miles for 220Wh/mi -> a 17 mile discrepancy in the rated range calculation. THIS CAR MAKES NO SENSE. Therefore, I conclude, the car pulls numbers out of its own arse for rated range display.


    range.JPG
     
  13. Cyclone

    Cyclone Active Member

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    Just to make sure I understood correctly. Right after the drive swap, this trip would use 223 Wh/mi and reduce your overall rated range by 92 miles. Now, a couple weeks later, you are getting about the same Wh/mi, but seeing less of a rated range drop. Correct? If so, are you still on .251 like before? Also, perhaps there was some sort of recalibrating going on that wasn't finished yet for tuning with the new drive unit before? It seems you have driven a little over 2k miles on this new unit, so perhaps the sensors were just off until you had more mileage on the drive unit.
     
  14. yobigd20

    yobigd20 Well-Known Member

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    Yep and yep
     
  15. dalamchops

    dalamchops Member

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    #15 dalamchops, Aug 3, 2015
    Last edited: Aug 3, 2015
    i completely agree that the car pulls random numbers out. I can drive my 1st 50miles and it uses exactly 50rated miles at around 300wh/mi, and when the car hits around 160 rated remaining, it starts using up rated miles/and kw twice as fast.
     
  16. trils0n

    trils0n 2013 P85

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    Last few months I've noticed this as well. Sometimes I get rated:driven at 1:1 at 300wh/mile. Sometimes 1:1 is 280wh/mile. Sometimes its 1:1 at 260wh/mile. Sometimes 1:1 at 308-310wh/mile. Same 120ish mile trip, hvac usage, etc. Log miles for work, and keep track of this. Usually it's around 290-300wh/mile to get rated range, but occasionally it's quite different. Seemed like first 2 years I owned the car it was pretty consistent in terms of wh/mile for rated:driven to be 1:1, but now does these odd things every once and a while.
     
  17. yobigd20

    yobigd20 Well-Known Member

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    all of my trips i've been monitoring since the DU are during the day in 70 degree weather and no hvac on at all so there should be absolutely no variation like this ....
     
  18. Matteo

    Matteo Member

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    hvac consumption counts in trip meter when in drive mode but doesn't count in park mode. Same with battery thermal management. In first trip, after you left with 220 rated miles and before you arrived with 130 mi, maybe you left the car in park mode for long time.

    By the way, for these calculations, I created a small calculator here. Go to page "Range Types Explained" and scroll down.

    Here is a screenshot:
    PR0f52U.gif
     
  19. yobigd20

    yobigd20 Well-Known Member

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    I understand what your saying but nope, not the case for me. Majority of the nights I plug in around 10pm with like 30-50 miles left and leave at like 4-5am right after it finishes charging so it's not left on or anything. Besides I have a habit of turning off the hvac if I had it on whenever I arrive home just for this specific reason of not wasting energy of doors are open or something while I'm loading or unloading my car.
     
  20. mikeash

    mikeash Active Member

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    Note that this is "rated range" which is quite different from "estimated"!

    An estimated range would take into account how you're expected to drive, current conditions, etc., and arrive at a number of miles you should be able to drive.

    Rated range is much simpler. It takes a fixed energy efficiency number (around 300Wh/mile, or roughly what you'll consume at a steady 70MPH with no climate control), applies that efficiency to how much energy is in your battery, and displays the resulting number. It has no relation to how you've been driving or what kind of conditions you're experiencing.

    If you want an estimated range, I believe you can get that by using the Energy screen. It will estimate your remaining range based on your average consumption for the last 5, 15, or 30 miles, depending on which scale you set it to display. Of course, if conditions up ahead are dramatically different from conditions behind you (say, you just came down a huge mountain, and you're about to go up another huge mountain) it could still be wildly off.
     

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