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Question about horsepower (Sport vs. non-Sport)

Discussion in 'Roadster: Technical' started by daniel, Nov 23, 2011.

  1. daniel

    daniel Active Member

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    Since people are always asking me about numbers, I figured I'd better look up the numbers for my non-Sport 2.5 model Roadster. Weight, number of battery cells, horsepower, torque. On THIS page, under the Performance tab, they say that both the Sport and non-Sport have 288 HP, but that the Sport has 295 ft-lbs of torque, while the non-Sport has 273 ft-lbs.

    Now, I don't pretend to understand this stuff very well, but I think that Power is (Force * Distance) / Time. Thus the motor with more torque should produce more HP.

    Have I got this wrong, or is there an error on the Specs page? And if the Specs page is right, that both models have the same HP, then what am I misunderstanding?
     
  2. torque can be converted to hp, I believe lb/ft of torque x rpm / 5252=hp...So I guess technically the Sport models do have more HP.
     
  3. VolkerP

    VolkerP EU Model S P-37

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    Hi daniel,

    smoothop is correct, power ~ torque x RPM. As in many cases, the full truth needs a diagram:
    torque.png
    You see that torque stays constant between 0-6400RPM, giving a linear power increase. From that on, torque is power-limited, and above 8000 RPM adverse effects in the electric motor decrease power output.

    The sport package delivers more amps, boosting torque but keeping the same power limit (since it is a limit of the pack). The sport motor has improved current capability but I don't know if it is more efficient.

    TEG should have power/torque diagrams for direct comparison of standard/sport motors at hand!
     
  4. daniel

    daniel Active Member

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    Thank you both. I think I understand now. And that makes sense of another point on the spec sheet that I didn't understand the significance of: While the Sport has higher torque, it maintains that higher torque to a lesser rpm:

    Non-Sport: Torque is 273 ft-lbs from 0 to 5400 rpm;
    Sport: Torque is 295 ft-lbs from 0 to 5100 rpm.

    If I apply smoothoperator's formula to those numbers I get 281 and 286 HP respectively at the top of the torque curve, which apparently is not quite the top of the HP curve.

    I also see that maximum HP for the non-Sport is from 5,000 to 6,000 rpm, whereas for the Sport is it 4,400 to 6,000 rpm, so although they have the same horsepower, the Sport delivers that maximum over a wider range of speeds.

    Those graphs are interesting. I didn't realize the way the power rises to a peak around 6,000 rpm and then drops off, or the way the torque drops off after 6,000. How fast is the Roadster going at 6,000 rpm?

    (As an irrelevant curiosity, the electric motor in my Prius has more torque than my Roadster. Of course, the Prius has nowhere near the power.)
     
  5. VolkerP

    VolkerP EU Model S P-37

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    Hi Daniel,

    Roadster max RPM is 14000 at a top speed of 125mph. Single gear = linear correlation. 6000 RPM is 53,5mh.
    That's why the speedometer and the RPM were unified into one display in Roadster dashboard, from 2.0 on IIRC.
     
  6. TEG

    TEG TMC Moderator

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    #6 TEG, Nov 23, 2011
    Last edited: Nov 23, 2011
    Related old discussions:
    Sport vs. Non-Sport the same motor?
    Changing torque curves

    Also a bit of comparison of Sport vs non sport:
    Torque-Curve2.png
    [​IMG]
    [​IMG]

    Basically you can see that the Sport model starts "off the line" with more torque and keeps it uniformly higher until it hits the "I need to start reducing torque" slope. The slope is similar for sport vs non-sport, but the sport has a higher peak initially, but eventually hits some higher RPM limitation that affects both models. (If you look closely you may notice that both models have about the same 150 ft-lb/lb-ft at 9K RPMs.)

    There are a bunch of factors involved including IGBT switching speeds, motor heat build up, back EMFs, etc.
    I don't pretend to understand all the things that make them have to design it to behave that way.
    But, I am convinced it is carefully tuned based on some engineering constraints they have to work around.
    I think the firmware controls this power delivery very precisely so it is all working "as designed."
     
  7. AnOutsider

    AnOutsider S532 # XS27

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    Volker also posted that graph. I notice power seems to fall off much earlier in the sport vs non-sport
     
  8. TEG

    TEG TMC Moderator

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    Yes, I know - and he requested it be compared to a graph for the Sport...
     
  9. TEG

    TEG TMC Moderator

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    #9 TEG, Nov 23, 2011
    Last edited: Nov 23, 2011
    I think the old chart first posted was pre 2010, pre 2.0. Maybe even for the prototype 1.0 drivetrain.

    Here is a mock-up of what 2.0 Sport vs non-sport might look like...
    sport-compare.jpg

    I think some of the confusion in this area is because of the old 1.0 & 1.5 power/torque charts which were published a while back.
    The 2010 & 2011 models with 2.0 powertrains have some different characteristics compared to the 2008s.

    (Getting historical here: Some of the very first Roadsters has 1.0 powertrains with much less low end torque. Those later got upgraded to 1.5 with a significantly improved PEM to make up for the loss of a lower gear. )

    There may be some hesitance to discuss differences in low end torque between 2008 and 2010 base models.
     
  10. speedy99

    speedy99 2.5 Roadster

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    I thought the Prius motor was only good for about 150 ft-lbs?!?! (and only a few thousand RPM)
     
  11. daniel

    daniel Active Member

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    My understanding is that the Prius electric motor (I presume they're talking about MG2, the main drive motor) produces 295 ft-lb of torque from 0 to 1,200 rpm. That's more torque than my non-Sport Roadster, but the same as the Sport model. But it's much less power due to the lower rpm limit.

    The Prius battery is much smaller, but the Prius is capable, when needed, of feeding power to MG2 from both the battery and from the ICE (via MG1) simultaneously.
     
  12. efxjim

    efxjim Member

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    The falloff in power is due to voltage limitations. A motor is like a generator. So at higher speeds it produces a certain voltage (regen) this voltage has to be overcome to get more ouput from the motor. If our pack had 600v it could do a better job of producing full output (less losses from switching and magnetic losses).
     
  13. TEG

    TEG TMC Moderator

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  14. TEG

    TEG TMC Moderator

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    Rather than doing more cross-posting, I am answering your question in this other thread:

    Sport vs. Non-Sport the same motor?
     
  15. daniel

    daniel Active Member

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    Thank you. I now understand. And thanks also to everyone who posted in this thread. The graphs, especially, and also the explanations, make it clear now how both models can have the "same" (max) HP but the Sport is the more powerful car. Or to put it another way, they explain why the car I knew to be more powerful has the same max HP as the less powerful car.

    Thanks to everyone.

    And I'm still very happy with my non-Sport Roadster. I didn't buy it for being a sports car after all, though I enjoy the sports-car aspect of it. I really bought it because it's electric and it can go on the freeway and it has more range than I need. And as an added bonus, it's the best color, IMO (Very Orange).
     
  16. TEG

    TEG TMC Moderator

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    Seems that TeslaMotors web site got updated with revised specs:
    Roadster Features and Specifications | Tesla Motors
    Interesting that they now show the non-sport as having slightly more max HP...
     
  17. vfx

    vfx Well-Known Member

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    So is that new cars being made in EU or will us drivers get a firmware HP bump?
     
  18. dpeilow

    dpeilow Moderator

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    Is this Roadster 2.6?
     
  19. doug

    doug Administrator / Head Moderator

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    That 1% might be in the noise. Power is just torque times RPM. Power is limited by the batteries (to first order). Since the Sport version starts with a higher torque, it reaches the power limit sooner (i.e. at a lower RPM). The difference might just be incidental, governed by the software.

    Did they advertise a power specs before for the non-sport? Seemed Tesla always seemed a bit coy with that info.
     
  20. TEG

    TEG TMC Moderator

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    The HP numbers have seemed to be oddly 'all over the place'. Not sure why...
     

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