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Why do diff battery packs have diff 0-60mph times?

Discussion in 'Model S' started by SoCalGuy, Jul 19, 2012.

  1. SoCalGuy

    SoCalGuy Member

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    Apologies if this has been discussed elsewhere (didn't easily find the answer in my search). Why do the 40/60/85 kwh packs also have different 0-60 times? I know the Performance version has a different inverter among other things. But doesn't the standard car have the same motor/inverter etc just diff energy capacities for batteries?

    Also, related question: why do the mileage estimates for range not scale linearly with energy capacity? Eg. If Tesla rated 40 kwh pack at 160 miles, why wouldn't an 85 kwh pack be rated at 340 miles (eg 85 x 160/40)? Why did Tesla rate it 300 miles?
     
  2. Mogwai

    Mogwai Member

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    The only reason I can think of the performance model being faster is there is either different motors, or a more advanced method of carrying electricity to the motors.

    As for the range, I think this may just be an estimate. I suspect real-world range tests will actually yeild a further range than stated by Tesla. VW does this with their TDI line-up so that customers expectations are not only met, but exceeded.

    Of course, I'm not very knowledgeable of the subject, and other members of the forum will likely provide you with more useful answers.
     
  3. adric22

    adric22 Member

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    I haven't seen any different 0-60 times advertised except for the signature (or performance) edition.

    However, if there are differences I would imagine the smaller battery packs can't handle the same amp draw.

    As for range, it isn't linear typically because when you add more batteries you also add more weight. Not only that, but smaller battery packs have to work harder to deliver the same number of amps. Faster amp draw typically means the battery will be less efficient (Peukert effect)
     
  4. SCW-Greg

    SCW-Greg Active Member

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    The Performance model has a different motor (more coil) and delivers more horsepower (416hp vs. 362).
    I believe the variance in the standard models with different battery packs, it the available peak output from the battery pack, or perhaps modified firmware as a perk for the bigger battery.
     
  5. stopcrazypp

    stopcrazypp Well-Known Member

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    The different 0-60 is because the smaller battery packs have less power (pack power is proportional to the battery size). It's also why the Fisker Karma is slower in Stealth mode (its ~20kWh battery is too small to output enough power). We have discussed this before in the Model S specs thread, but it's a bit buried:
    http://www.teslamotorsclub.com/showthread.php/2478-Model-S-specs/page40?p=99335&viewfull=1#post99335

    As for the different efficiency, it's because the 40kWh (~5500 cells) will definitely have significantly lower weight than the 85kWh. The 60kWh and 85 kWh is projected to have similar weight (because Tesla has said they will use the same number of cells: ~7800, just higher capacity cells for the 85kWh). There is some indication that this may change for the 60kWh pack though (Tesla might decide to use less cells). We have also discussed the efficiency difference for the 40kWh here:
    http://www.teslamotorsclub.com/showthread.php/7155-Mystery-of-the-Missing-5-kWh
     
  6. Andrew Wolfe

    Andrew Wolfe Roadster 472 - S 440

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    #6 Andrew Wolfe, Jul 19, 2012
    Last edited: Jul 19, 2012
    Many of these answers are wrong.

    Tesla has provided 0-60times for each model. http://www.teslamotors.com/models/options

    The Performance Model S has the same motor (based on public statements), but has a 1200A inverter instead of a 900A inverter. This provides more power to the motor.

    The other models have the same motor as well. The reason for less power is not fully known, but the 40KW and 60KW models have fewer or lower capacity cells. Fewer cells means that at the same power per cell there is less total power. In any case, Tesla has chosen to limit the peak power based on some combination of:

    1) A fundamental limit on the safe power per cell (and fewer cells in the 40KWH model)
    2) A desire to increase durability on smaller packs (that will have more charge cycles)
    3) A desire to make more expensive cars more attractive.

    I suspect that the first two issues are the important ones.

    As to why range does not scale linearly - again, nobody knows for sure - but it is some combination of:

    1) Increased weight with larger packs
    2) Using less of the capacity of larger packs to allow increasing the warranty.
     
  7. MikeK

    MikeK R#129, TSLA shareholder

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    My understanding is that the Performance cars use exactly the same motor, but use a different inverter, strengthened gears, and strengthened half shafts.

    I believe that the 60kWh and 40kWh battery packs are able to provide less current than the 85kWh pack, and this accounts for the longer 0-60 times.
     
  8. SCW-Greg

    SCW-Greg Active Member

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    Thanks Andrew. I stand corrected. Good to know.
     
  9. richkae

    richkae VIN587

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    #9 richkae, Jul 19, 2012
    Last edited: Jul 19, 2012
    I heard something really interesting from an EV drag racer, and I will attempt to paraphrase.

    "In an EV the battery makes horsepower and the motor uses that horsepower."
    You build the motor "big enough" to use all the power the batteries can provide, but it is the simpler/cheaper component in the system - the batteries are the important part.

    Batteries are measured both by their capacity ( store energy ) and their ability to deliver current ( deliver power ).
    The power delivery is also usually further broken down into continuous versus burst.

    The batteries in the Model S probably are used at around 4C when bursted. This means the 40kWh battery delivers 160kW ( 215 hp ) and the 85kWh battery delivers 340kW ( 456 hp )

    There are batteries that can be used at much higher C rates ( like 25C or even higher ) in bursts, and that is what EV drag racers use.
    So a 20kWh pack can deliver 670 horsepower. However they tend to be much less energy dense.
     
  10. Main reason IMO
     
  11. Zextraterrestrial

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    but not the truth..

    add in the wiring needed to handle the added amps and other electric components and the cost is there.
    copper and gold are pretty expensive
    Newer cells can take 60C bursts + (but probably not the same form factor cells)
     
  12. stopcrazypp

    stopcrazypp Well-Known Member

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    Disagree completely. See rickrae's comment. The 40kWh pack can only output 160kW (215hp) in bursts. For a 4000+lb car, a 0-60 time of 6.5 seconds is about right with that horsepower. Even if Tesla wanted to provide the same acceleration/power as the 85kWh pack, they can't.

    Again, the Fisker Karma has the same issue (not enough pack power) and it already uses a123 cells (and these can run at 10C continuous and up to 50C for a 10 second burst, Fisker is only using it at about 9C max for 180kW of battery power). If Tesla switched to these high power cells the 40kWh battery pack would cost and weight more than the 85kWh pack, which would have been pointless.
     
  13. Check out the difference in packs between the Roadster and Roadster Sport
     
  14. Zextraterrestrial

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    same pack,
    one hand wound motor and one not. Maybe more pure strands of copper too

    there isn't that 'huge' of a difference between the two, just more torque with the sport
     
  15. grisnjam

    grisnjam P6316

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    +1 From my days of model airplanes and li-ion packs I would bet the above is the main reason for the differences. The motor is the same in all the Model S versions but the effective HP you get out of that motor depends on the max draw from the battery pack.
     
  16. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Active Member

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    Precisely. The different levels are about battery durability and it should be an advantage for larger batteries in normal driving.

    Small batteries limit output due to durability, but the motor and inverter can be smaller too to save money.
    As battery size increase the stable output increases but the motor and inverter need to be larger to handle all-electric driving.
    Then additional battery can be added to increase capacity with the same sized motor and inverter and that will also help with durability as the average current draw will be lower.
    The Model S Performance obviously can draw so much current that it needs a larger inverter, although they may also be making you Performance buyers pay for increased chance of using the warranty. ;)
     
  17. richkae

    richkae VIN587

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    The difference between the Roadster and the Roadster sport is that the Roadster has extra battery horsepower available that it can't use because the motor and/or PEM is limiting it. I said that you build the motor to use all your available battery horsepower because the motor is cheap compared to the battery. Tesla discovered that they got it wrong the first time and the motor was limiting the car, so they made a better motor and charged more money for it.
    I am an acceleration junkie and was not willing to pay $20k for the marginal improvement of the sport even though I do regret not getting the adjustible suspension.
     
  18. WarpedOne

    WarpedOne Supreme Premier

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    Same packs, but Roadster Sport is even weaker than regular roadster:
    Roadster: 225 kW
    Roadster Sport 223 kW

    Where Sport version shines over regular is at low speed acceleration.
    Fixed gearbox means max available power rises as vehicle spead increases (until the torque starts to fall off).Sport can pump 33% more amps through the motor at these low speeds/RPM:

    As it has been said: 40kWh battery can output up to 160kW, 60kWh up to 240kW and 85kWh up to 340kW of power at the same "cell-power level".
    Hence smaller battery means not just lower range but also less power.
     
  19. rsquared99

    rsquared99 Member

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    John V said in his second review today: "The 2012 Tesla Model S has a larger battery pack that forms the floorpan of its all-new design, but its 270-kW (362-hp) motor still powers the rear wheels. The Performance model has a more powerful 301-kW (416-hp) motor." So he's been led to believe there is a different motor size.
     
  20. gg_got_a_tesla

    gg_got_a_tesla Model S: VIN P65513, Model 3 Res Holder

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    Small typo by him there btw; the perf motor's rated at 310 kW, not 301.

    Model S Options and Pricing | Tesla Motors (see the "Battery and Performance" matrix)
     

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