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Calculate usable battery capacity based on rated miles values

Discussion in 'Model S: Battery & Charging' started by wk057, Jan 15, 2017.

  1. apacheguy

    apacheguy S Sig #255

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    My guess would be that the explanation lies in the deviation of SOE and SOC as suggested in my post quoted above. Although, I have yet to test this and it likely doesn't apply equally to all cars.
     
  2. wk057

    wk057 Senior Tinkerer

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    • Like x 6
    • Informative x 1
  3. NateZ

    NateZ Member

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    Great info. Thanks!

    The P100D had an EPA "Combined range voluntarily lowered to 315 miles" (305.9 city & 346.9 highway). Is this the reason why your capacity calculation was less than actual?
     
  4. David99

    David99 Active Member

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    This is exactly what Tesla wrote in an email to a concerned customer who saw his range drop. Thanks a lot for explaining this from a more technical point of view!
     
  5. David99

    David99 Active Member

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    You mentioned many times there is no extra capacity passed zero. Just to clarify, when you refer to zero, you mean the actual 0% state of charge on the battery, not when it shows zero miles left. We know Tesla prevents the battery to be discharged to true 0% to protect the battery. I and many others have been able to drive beyond the point when the car showed zero miles left. When I reach 0 miles and 0% (on the dash) the car still shows aprox 4% SoC on the CAN bus. How much of that you can use seems to depend on several facts and yes there is no guarantee the car let's you use any of it, but I just want to clarify when you refer to 0 (zero) you mean the actual true 0% SoC, correct?
     
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  6. apacheguy

    apacheguy S Sig #255

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    @David99 you are getting at the same point I made earlier. I believe on cars where SOE > SOC at the low end, it makes sense that we should follow SOE. This is because SOE does not include bricking protection.

     
  7. Yoshi

    Yoshi Member

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    Wait a minute... I have the S70, with the 75 battery pack but I didn't do the software upgrade. So I have only 65.9 kWh? If I look at all the figures, this is the worst scenario. It says the normal 75 has 72.6 kWh usable, so an upgrade would give me 6.7 kWh extra.

    However, since I'm software limited, does it mean I can charge the battery to 100% every time without doing it any harm?
     
  8. wdolson

    wdolson Well-Known Member

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    I did some calculations a while back on the actual battery sizes going from the cell capacity up. I adjusted my figures to come as close as possible to Jason's numbers, but couldn't quite match them perfectly. It looks like the 70 pack has more cells per module than the 60 pack did for the math to work right.

    If you could point out anywhere I made any errors I'd appreciate it. 2017-01-25_001.png

    2017-01-25_001.png
     
  9. transpondster

    transpondster Member

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    I thought 70 pack had the same modules as 85 and 75 same as 90.
     
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  10. wdolson

    wdolson Well-Known Member

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    If it did, the 70 pack would actually be 70.4 KWh and the 75 would actually be 77.1 KWh.
     
    • Disagree x 1
  11. rowdy

    rowdy Member

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    Yep it did.

    70 pack has 14/16 modules of 85 pack. i.e. 87.5% of 85 pack
    75 pack is 14/16 of 90 pack. i.e. 87.5% of 90 pack

    the table is incorrect. Should have 444 cells/module for both 70 and 75 packs. Only difference is 14 modules instead of 16
     
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  12. transpondster

    transpondster Member

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    I think you used either big packs numbers not from here or mulfunctioning calculator :p, because I get 71,3125 and 75,075. Also I suspect modules and cells ar binned so diffrence of at least 0,5 kWh would be normal
     
  13. Olle

    Olle Member

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    @wk057:
    1. when you looked at the software limited 60 and 70 packs, did you see how much of the software limitation that was placed bottom and top of SOC respectively?
    2. In regards to bottom SOC limitation on these software limited packs, do you know if that bottom limitation temporarily unlocks if you hit 0 miles? or is it programmed to shut down the car just like the non limited packs?
    3. I have the limited 70. 65900 Wh/295 Wh/mile =223.4 miles. But it always shows the advertised 230 Rated Miles at full charge. How could this be?
     
  14. wdolson

    wdolson Well-Known Member

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    I think I rounded off too much, but I still have some math that doesn't work for the new pack. Elon has said the new 100 KWh pack uses the same cells as the 90 KWh pack and wk057 has said there are 516 cells per module. Using the calculated values for the NCR18650Gs that work for the 90 and 75 packs, that comes up with only 99.7 KWH for the 100 KWh pack, but wk057 found the pack has a rating of 102.4 KWH. That would imply a new cell with a slightly higher AH rating. Unless I screwed up my math again.

    Another thing I found when running the numbers is they can make a 90 KWH pack that more closely matches 90 KWh by using 14X of the new modules that go into the 100 KWH pack. Both using the numbers from the NCR18650G and the possible new cell come up with a higher KWH rating than the current 90 KWH pack.

    Once production of the 100 KWH pack gets up to speed, they might bump of the range of the 90 KWH pack, or drop the 75 KWH pack entirely. They may do this when the Model 3 is introduced to keep a bigger gap between the Model 3's top of the line and the bottom of the Model S's line. They could always do a software restriction on the pack to offer something smaller than 90 KWh.

    2017-01-25_004.png
     
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  15. transpondster

    transpondster Member

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    hmm yes from reported pack capacity and cell count there is ~2,5% increase in cell capacity
     
  16. Yinn

    Yinn Active Member

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    I don't have any window stickers, but these seem to different from FuelEconomy.gov which gives these figures for the 2017 models. I'm not sure if they changed over time or why it differs from the internal firmware.

    Model X 75D: 360wh/mi for 238mi range
    Model X 90D: 370wh/mi for 257mi range
    Model X P90D: 380wh/mi for 250mi range
    Model X 100D: 390wh/mi for 289mi range.

    It allows customization, but I left it at default EPA figures. I tried doing a max 100% local and 100% highway, and the lowest those figures go to is 350wh/mi for the MX 75D. Those seem awfully high though. It would imply the 100D carries a 112kw pack. Either way, any insight on why the internal rated system is so different from the EPA's own website?

    **I use ~350wh/mi on a refresh S60D for range nowhere close to 217mi, my own numbers are more in line with your findings with ~180mi out of a 100% SOC @ 350wh/mi.
     
  17. ohmman

    ohmman Plaid-ish Moderator

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    Yeah, those are way off. I don't know why those are published that way. Clearly someone very bad at math put that together.
     
  18. apacheguy

    apacheguy S Sig #255

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    The 85, 90, and 100 have a bottom range buffer of 4.0 kWh. The 60 I believe has 2.5 kWh. There is no way to "unlock" this buffer even if you hit 0.
     
  19. ran349

    ran349 Member

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    Those numbers include charging efficiency losses and that is why they are higher.
     
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  20. ohmman

    ohmman Plaid-ish Moderator

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    Charge efficiency appears to be in the 90% range, if I'm not mistaken. So, scaled:

    Model X 75D: 360Wh/mi (324Wh/mi) for 238mi range - 77112Wh usable pack equivalent
    Model X 90D: 370Wh/mi (333Wh/mi) for 257mi range - 85581Wh usable pack equivalent
    Model X P90D: 380Wh/mi (342Wh/mi) for 250mi range - 85500Wh usable pack equivalent
    Model X 100D: 390Wh/mi (351Wh/mi) for 289mi range - 101439Wh usable pack equivalent

    The numbers still seem high across the board, but especially for the 75/100. Or I did something wrong.
     

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