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70D and 85D highway MPGe compared

Discussion in 'Model S' started by jgs, May 27, 2015.

  1. jgs

    jgs Member

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    Here's something curious I haven't seen discussed yet. Looking at the 70D and 85D on the EPA fuel economy site, as expected the 85D gets a somewhat lower city MPGe rating then the 70D, 95 vs 101 to be precise. However, for some reason it has a better highway rating – 106 versus 102. The lower city rating is not surprising, the 85D must be heavier since it's carrying more batteries. However, I'm curious why the highway rating would be better. I had the impression the two cars were essentially identical other than their battery packs.
     
  2. No2DinosaurFuel

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    I think I discussed this already. Not specifically in a separate thread, but when comparing the 2. I am too lazy to look this up right now. But my conclusion is the 70D is more efficient overall, but I would get the S85D because of the HWY efficiency. Having a Model S means you will not need to worry about the city MPGE because you will have plenty of charge to make it anywhere in the city the whole day. However when you venture outside the city, this is when you need to worry about charge or the HWY efficiency.

    Bases on these numbers, I am holding out for a CPO S85D or inventory S85D. I was originally considering the S70D, but it would do horribly compared to the S85D on the HWY.

    I think the difference is the battery voltage of the two cars. The S70D uses the same voltage as the 60KWh battery which is lower than the 85KWh battery. I suspect Tesla optimize BOTH the CITY and HWY range at the lower voltage when choosing the different front and back motors. They just used the same setup for the S85D and tweaked the algorithm to use the more efficient motor at higher speed more often on the HWY to get the S85D HWY MPGE.
     
  3. jgs

    jgs Member

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    The front and rear motors on the 70D and 85D are identical. It's just the P85D that uses a different motor on the rear axle.
     
  4. No2DinosaurFuel

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    I don't think they are the "same" motor. They might be the same size, but probably wound different for different optimal operating RPM. I think I read this somewhere.
     
  5. stopcrazypp

    stopcrazypp Well-Known Member

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    Higher voltage means less resistive losses at the same power due to lower current required. That may play a factor all else being equal.
     
  6. lolachampcar

    lolachampcar Active Member

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    also lower discharge per cell or C rate improves available cell capacity
     
  7. Damiano

    Damiano Member

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    Agree. Also add to that battery management is probably more efficient in the 85 versus the 70 on a per kWh basis.
     
  8. chriSharek

    chriSharek Member

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    There's 329 hp vs 422 hp right on the design site! Are you suggesting that it's strictly due to the battery size? From a manufacturing standpoint I can see your logic, but another (almost) 100 hp just due to how quickly they can pull from the bigger battery? I don't think so . . .
     
  9. jgs

    jgs Member

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    Makes more sense than thinking they would go to the expense and logistical trouble to source a different motor. Two other possible explanations are inverter, or software (which I think is least likely, but still more likely than a different part for the motor).
     
  10. No2DinosaurFuel

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    If you increase voltage you will increase power of the motor. Both Voltage and Current are increased assuming the same controller with same software with same FET or IFGBT in this case probably due to the massive voltage. Even if the controller are scaled to somehow keep the same current, you just increased your power because of the increase in voltage. Power = Current * Voltage.
     
  11. breser

    breser AutoPilot Nostradamus

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    The 85D was limited to the performance characteristics of the 70D until a software update. They're probably limiting the performance of the 70D in software to some extent in order to increase the apparent value of the 85D.

    But there's probably something to the things that stopcrazypp and lolachampcar mentioned. The 85 kWh battery should have higher voltage than the 70 kWh battery.
     
  12. chriSharek

    chriSharek Member

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    P = A * V. I get that. I just don't want to believe there is the same size motor in the 70D and 85D if I'm paying the additional $10k for the 85D!

    I guess I value the added range as well as the increased performance, but it doesn't seem right for performance to be around 25% better (97 hp) using the same motors.
     
  13. travwill

    travwill Member

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    I think they are the exact same. You are mainly paying for the larger battery pack in turn that also enables the them to draw a little more power from it for better optimized performance - all software controlled most likely. The 70 just has some empty cells I believe filling the space...
     
  14. vvanders

    vvanders Member

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    Chances are the inverters are a bit different. I would guess they have a bunch in parallel and can leave some unpopulated on the 70D for streamlined production.
     
  15. No2DinosaurFuel

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    Not sure what you mean by bunch of inverters in parallel. My guess is it is rhe same inverter. The voltage input is different hence the difference in performance. If you mean there is a lack of IBGT drivers then maybe... But i doubt tesla would make a different inverter and different software for each inverter. It will be simplier and easier to maintain one software for 1 inverter and let the voltage difference determine the performance.
     
  16. tom66

    tom66 Member

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    Sorry to bump -- but does anyone know what the actual battery voltage of the 70D is? Is it 350V like the 60kWh?
     
  17. No2DinosaurFuel

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    This was confirmed by some 70d owner supercharging. It is indeed lower voltage compared to the 85kwh battery. The voltage is the same as the 60kwh battery.

    Take a look at this thread:

    Supercharging the 70D - Page 2
     
  18. S4WRXTTCS

    S4WRXTTCS Active Member

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    Yeah, it's 350V.

    As an owner of a 70D I've been meaning to test out the REAL WORLD range of the 70D, but I haven't gotten around to it. I have 1250 miles on my barely 2 week on 70D and I haven't done anything I said I was going to do.

    The problem is all these things we worry about online don't matter in real life.

    In real life it accelerates so fast it exceeds whatever the speed limit is within a blink of an eye. I have the speed limiter warning set for 10 over, and it constantly blinks at me when I accelerate.

    I can't grab any meaningful numbers because I keep hitting the throttle like it a monkey would hit a switch to get a banana.

    Then the supercharger gets done with a charge even before I finished my dinner let alone have gotten the check.
     
  19. 3mp_kwh

    3mp_kwh Member

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    Consider that the 85D to 85 highway MPGe number difference isn't anywhere close to real world, at 106 vs. 90, while Breser's thread puts those two cars just about on top of each other.
    http://www.teslamotorsclub.com/showthread.php/44011-Real-World-Comparison-of-a-S85-to-an-85D-Efficiency (he owns the 85D).
    There are legitimate criticisms of real-world tests, but I would still go by them over setting myself up for disappointment. I don't think in any test we could perform, we would find the 85D is 18% more efficient than the 85. It would be better to pair a 70D and 85D together, and do something similar to his thread. Better yet, do a driving cycle that mimics how you'd use the cars.
     
  20. breser

    breser AutoPilot Nostradamus

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    Find me someone with a 70D in the area and we can see if we can't get a 70D, 85D and 85 all together.
     

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