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Motor-battery combo performance differences S60, S85, and P85

Discussion in 'Model S: Driving Dynamics' started by chrisdl, Sep 18, 2013.

  1. chrisdl

    chrisdl Member

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    #1 chrisdl, Sep 18, 2013
    Last edited: Sep 20, 2013
    Drivetrain-battery combo performance differences S60, S85, and P85

    On the official Tesla Motors forum there was a thread where someone asked where the difference in performance between de S60, S85, and P85 came from. Well, I did some digging and found some answers. I thought these answers where interesting enough to share with TMC. Feel free to kick my $ss if you don't think so :wink:

    Anyways, here's my post:


    What have we learned so far:
    (Side note: Some numbers are approximate (but all are based on actual specs!), however they still give quite an accurate idea of what you can do with each drivetrain / battery combo.)

    UPDATE 1 (green)
    - more accurate cell count per battery
    - increased maximum load current of a single cell to 12.5 A
    - replaced 'motor' by 'drivetrain' to avoid motor/inverter discussions

    UPDATE 2 (purple)
    - more accurate charging voltage (mainly changing the 60 kWh calculation)

    Thank you all for the invaluable input!


    1. S60 and S85 have the same drivetrain, but different batteries.
      P85 has another, more powerful drivetrain.

    2. Motor specs (from Tesla website)
      Power:
      S60: 285 kW - S85: 285 kW - P85: 350 kW (WITHOUT taking battery into account = theoretic)
      S60: 225 kW - S85: 270 kW - P85: 310 kW (power WITH battery taken into account = realistic)

      Torque:
      S60: 440 Nm - S85: 440 Nm - P85: 600 Nm

    3. Number of cells per battery (each cell has a capacity of approx. 12 Wh, rounded for simplicity's sake)
      => 60 kWh battery has about 5040 cells
      => 85 kWh battery has 7104 cells (confirmed information from Tesla)

    4. Battery is charged at supercharger at 4.2 V charging voltage per cell
      * 60 kWh battery tops off at 352 V
      => 352 V / 4.2 V = 84 cells in series in a single bank
      * 85 kWh battery tops off at 402 V
      => 402 V / 4.2 V = 96 3.6 V battery cells in series in a single bank

    5. Number of banks per battery
      * 60 kWh battery has 60 banks of 84 cells
      * 85 kWh battery has 74 banks of 96 cells

    6. Maximum discharge current is 12.5 A per cell (based on 2) and 7))
      * 60 kWh
      => 12.5 A per bank of 84 cells
      => 60 x 12.5 A for 60 kWh battery = 750 A
      * 85 kWh
      => 12.5 A per bank of 96 cells
      => 74 x 12.5 A for 85 kWh battery = 925 A

    7. Maximum discharge power at nominal cell voltage of 3.6 V:
      * 60 kWh battery:
      => 3.6 V x 84 cells = 302 V
      => 750 A x 302 V = 227 kW
      * 85 kWh battery:
      => 3.6 V x 96 cells = 346 V
      => 925 A x 346 V = 320 kW

    Comparison drivetrain power output versus battery power output:
    * S60: 285 kW vs
    227 kW (battery limited)
    * S85: 285 kW vs 320 kW (drivetrain limited)
    * P85: 350 kW vs 320 kW (battery limited)


    Conclusion:

    • S60 is limited by maximum battery discharge rate of 60 kWh battery
    • S85 is limited by maximum power of drivetrain
    • P85 is limited by maximum battery discharge rate of 85 kWh battery
    Optional information regarding energy loss in the battery due to the cells' internal resistance:

    8) Power loss in battery cells (dissipated heat)
    The internal resistance of a fresh battery cell is about 100 mOhm (0.1 Ohm)
    => S60: 750^2 x 0.1 = 56 kW
    => S85: (285 kW / 346 V )^2 x 0.1 = 68 kW
    => P85:
    925^2 x 0.1 = 86 kW

    9) Total energy usage in battery (power output + heat loss):
    => S60: 227 + 56 = 283 kW
    => S85: 285 + 68 = 353 kW
    => P85
    : 320 + 86 = 406 kW

    References:
    High Power Wall Charger - Actual DC Volts/Amps Going To Battery?
    Battery facts?
    Analyzing car efficiency at different power outputs (accelerations) | Forums | Tesla Motors

    Model S Options & Pricing | Tesla Motors (may not be the same, depending on your country)

    industrial.panasonic.com/www-data/pdf2/ACA4000/ACA4000CE240.pdf
     
  2. Bobfitz1

    Bobfitz1 Member

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    Nice! But contributing to TMC means never having to ask to get kicked if your facts are off the mark!
     
  3. chrisdl

    chrisdl Member

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    Gotcha, Bobfitz1. A point well made.
     
  4. mnx

    mnx 2013 P85

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    So a future ~95kWh battery (assuming similar specs) could raise the performance of the P85. Cool!
     
  5. jja

    jja Member

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    I thought the P85 has the same motor, a P85 has larger inverter.
     
  6. gocken2

    gocken2 Model S: P6931

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    I agree, TM has never said anything about a different motor. That was early speculation on TMC based on the Roadster motors.
     
  7. chrisdl

    chrisdl Member

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    gocken2, jja:
    To shortcut this discussion, feel free to replace all instances of "motor" by "motor-gearbox-inverter" or "drivetrain". It makes no difference to the calculation. I'll edit the message to reflect this more clearly later. (First I have to build a Playmobil Hotel with my little daughter. It's her birthday!)
     
  8. patn

    patn Member

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    Great work. What I'm hoping we'll find out in the future is how much power output is affected by charge level and temperature.
     
  9. scaesare

    scaesare Active Member

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    Something I've wondered about but never got around to posting:

    Does the P85 display indicate in can draw more than 320KW from the pack? In my test drive of a P85, and in my short stint with a loaner, I thought the display on the dash indicated the same top-end energy limit of ~320KW (there is at least one small hash mark above that).

    My Standard 85 can get close to that 320 mark in utilizing energy... can the P exceed it substantially?
     
  10. islandbayy

    islandbayy Active Member

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    The P85's DO have a DIFFERENT motor AND Inverter. I have confirmed this at the Villa Park service center (I ask lots of questions ;)

    The rough numbers I was told was 1200 amp on the P85's, and 800 amp on the Standards for motor and controller capacity. Though, they were slightly unsure about those numbers, but confirmed their are different motors and inverters (also known as the controller) in the P models.

    BTW, My MS60 Draws up to 240kw at max accel. Now, 225 is the "official" number. Though, for short bursts, I do not see 240kw hurting anything. Though, the accel limiter quickly kicks in much more quickly in the MS60 then in the MS85 or P85's (I have gotten to play with every model tehe).
     
  11. brianman

    brianman Burrito Founder

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    Keep in mind that these are advertised values. Actual values may exceed them (briefly).

     
  12. chrisdl

    chrisdl Member

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    1200 A for P85 vs 800 A for S85 would mean that the P85 drivetrain is 50% more powerful than the S80's. That does sound a bit too much of a difference.
    According to the Tesla specs, the difference in the power output of the P85 vs S85 is less than 25%.

    Taking the pure drivetrain power output, a P85 would draw about 1000 A and a S85/S60 would max out at 800 A.
    I guess that's what the people were referring to. So they were not that far off and only had 1 number wrong! :)
     
  13. stopcrazypp

    stopcrazypp Well-Known Member

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    Tesla directly said in PR that the only difference between the P85 and S85 is an upgraded inverter that allows 1200A vs the 900A the standard inverter allows:
    http://www.thechargingpoint.com/news/Tesla-announces-Model-S-performance-version.html

    There is no difference in the motor between the three versions (I remember this very clearly because this is completely different from the Roadster, where Tesla made a big deal about the different hand-wound motor in the Sport version).

    The service people might think both the motor and inverter are different because AFAIK they remove the both as a single unit during service.
     
  14. qwk

    qwk Model S P2681

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    The service centers only remove and replace the batteries and entire drive units. They really don't know much about internal differences.
     
  15. captain_zap

    captain_zap Electron tamer

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    I think your conclusion is accurate. To further refine your calculations, the number of cells in the MS pack has been previously reported to be 7104, in a 96-series, 74 parallel configuration. The cells are 3.1 A-h, so at an average discharge voltage of 3.6v, would be about 11.2 W-h per cell. http://www.teslamotorsclub.com/showthread.php/17590-Model-S-Battery-Pack-Cost-Per-kWh-Estimate/page8
     
  16. chrisdl

    chrisdl Member

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    brianman:
    Yes, absolutely! The 10A maximum current I used in my calculation is no hard limit. It is possible to draw a higher current from a single cell, but Tesla likely limited that to ensure the cells did not overheat. I just used 10A to simplify things (and because it is pretty accurate anyway).

    stopcrazypp:
    The more official data, the better! The numbers listed, although probably accurate (at the very least at the time of the press release, because who know what Tesla changed/optimized in the meantime), conveniently don't make any difference in the calculation. I will incorporate them for the sake of completion, though. Thank you.

    captain_zap:
    Thank you! I'll incorporate this information in my calculation.
    Indeed, I have read the Panasonic specs and I've seen that the cells have a capacity of 11.2 Wh. I rounded it down to 10 Wh for simplicity, just like I've round other numbers, lazy me.
     
  17. chrisdl

    chrisdl Member

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    #17 chrisdl, Sep 19, 2013
    Last edited: Sep 19, 2013
    Thank you all for the updated information to make my calculation more accurate. It seems that the biggest mistake I made was assuming that the peak current drawn from a battery cell is 10 A. The cells do allow more to be drawn, obviously, and so it seems to be as well, given the information I got pointed to by the nice people on this forum. A single cell can deliver 12.5 A in my latest calculation. Now, as some have pointed out, both the instant power gauge and the API regularly indicate a higher power output than the specified 225 kW / 270 kW / 310 kW respectively. Does this mean that Tesla allows short burst of higher power? Or is the power measurement system inaccurate? I don't know. Any help is, as always, very welcome.

    Changes to my calculation are in green.

    1) S60 and S85 have the same drivetrain, but different batteries.
    P85 has another, more powerful drivetrain.

    2) Motor specs (from Tesla website)
    Power:
    S60: 285 kW - S85: 285 kW - P85: 350 kW (WITHOUT taking battery into account = theoretic)
    S60: 225 kW - S85: 270 kW - P85: 310 kW (power WITH battery taken into account = realistic)
    Torque:
    S60: 440 Nm - S85: 440 Nm - P85: 600 Nm

    3) Number of cells per battery (each cell has a capacity of approx. 12 Wh, rounded for simplicity's sake)
    => 60 kWh battery has about 4992 cells.
    => 85 kWh battery has 7104 cells (confirmed information from Tesla)

    4) Battery is charged at 360 VDC at supercharger
    => 96 3.6 V battery cells in series in a single bank

    5) Number of banks per battery
    * 60 kWh battery has 52 banks of 96 cells
    * 85 kWh battery has 74 banks of 96 cells

    6) Maximum discharge current
    Maximum discharge current is 12.5 A per cell (based on 2) and 7))
    => 12.5 A per bank of 96 cells
    => 52 x 12.5 A for 60 kWh battery = 650 A
    => 74 x 12.5 A for 85 kWh battery = 925 A

    7) Maximum discharge power, at 346 V per bank
    * 60 kWh battery: 650 A x 346 V = 225 kW
    * 85 kWh battery: 925 A x 346 V = 320 kW

    Conclusion:
    * S60 is limited by maximum battery discharge rate of 60 kWh battery
    * S85 is limited by maximum power of drivetrain
    * P85 is limited by maximum battery discharge rate of 85 kWh battery

    References:
    High Power Wall Charger - Actual DC Volts/Amps Going To Battery?
    Battery facts?

    EDIT: (added heat dissipation numbers)

    8) Power loss in battery cells (dissipated heat)
    The internal resistance of a fresh battery cell is about 100 mOhm (0.1 Ohm)
    => 60 kWh battery: 650^2 x 0.1 = 42 kW
    => 85 kWh battery: 925^2 x 0.1 = 86 kW


    9) Total energy usage in battery (power output + heat loss):
    => 60 kWh battery: 225 + 42 = 267 kW
    => 85 kWh battery: 320 + 86 = 406 kW

    And additionally:
    Comparison drivetrain spec power output versus battery power output:
    * S60: 285 kW vs 225 kW (battery limited)
    * S85: 285 kW vs 320 kW (drivetrain limited)
    * P85: 350 kW vs 320 kW (battery limited)
     
  18. scaesare

    scaesare Active Member

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    This leads to my question above....does the dash power meter on the P85's indicate it can draw ~400KW as opposed to the 320KW on a Standard 85?

    Or is it that the "needle" in the Std85 never qute makes the 320 mark (mine seems to only get close), whereas the P85's have needles that swing to the hash marks past the 320 demarcation?
     
  19. jcaspar

    jcaspar Member

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    Same drivetrain (motor) for all models, just different inverter for the P's is what I have been told.
    I wouldn't consider the inverter part of the drivetrain but maybe that is old ICE thinking. Seems like the equivalent of an intake manifold in ICE terms...
     
  20. ToddRLockwood

    ToddRLockwood Active Member

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    From a manufacturing perspective, there would be a lot more efficiency in making one motor for all three models, and I believe this is what Tesla did. The differences are in the inverter and software.
     

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