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How does "Power Limited" compare with other modes?

Discussion in 'Roadster: Technical' started by S-2000 Roadster, Jul 7, 2011.

  1. S-2000 Roadster

    Joined:
    Apr 10, 2009
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    636
    Ok, so we have several modes and submodes available for the Tesla Roadster power. Where does the "Power Limited" mode fit within the spectrum? I'm talking about when the light on the instrument cluster is lit (which, thankfully, I've never seen).

    ft-lbs of torque per Mode
    295 Performance (white)
    273 Performance (red)
    265 Standard
    ??? Range (50% power, not a torque limit?)
    ??? Power Limited
    ??? Valet (is this different than Range or Reserve modes?)
    ??? Reserve

    Note, I'm not sure whether the last few "Modes" are literally distinct, but since they have different names I'm wondering whether they have unique torque and/or power limits.

    Also, since the Roadster controls motor torque in proportion to the accelerator pedal, how does this relate to power? Is there a fixed ratio between power and torque, or do certain conditions allow them to be independent? I must admit that I have not stared at the Torque, Power, and G-force display long enough to tell, and my school physics classes are a bit too long passed to recall.
     
  2. W.Petefish

    W.Petefish Active Member

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    I am no stranger to the Power Limited light. I have on many occasion got the PEM's temp into the first yellow in which the PEM decides to limit the power to cool down.

    Power limited limits you to 50KW draw.
    Range Mode as far as I can tell just limits the amperage to below 400 amps.
     
  3. S-2000 Roadster

    Joined:
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    Thanks for the reply.
    Does this correspond to a specific horsepower limit? If so, what hp?
    Does this correspond to a specific torque limit? If so, what?
     
  4. mnx

    mnx 2013 P85

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    Ancaster, Canada
    #4 mnx, Jul 8, 2011
    Last edited: Jul 8, 2011
    1 kilowatt = 1.34 hp
    50kW x 1.34 = 67hp.

    To figure out the power provided under the 400amp limit, you can multiply by the pack voltage of 375V to get the power limit in kW.
    400A x 375V /1000 = 150kW.

    150kW x 1.34 = 201hp.

    There are probably some small efficiency losses from the pack to the motor, so these figures would be actually slightly lower.. Knocking off another 10% would probably be a good guess. So 60hp and 181hp are the #'s.

    Since all your other #'s are in ft-lbs we can convert to those as well.

    I believe max torque is available from 0-6000rpm, so...
    60hp x 6000rpm / 5232 = 68 ft-lbs
    181hp x 6000rpm /5232 = 207 ft-lbs



    - mnx
     
  5. S-2000 Roadster

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    Thanks, mnx.

    I had a feeling that kilo-Watts translated directly to horsepower and British horsepower.

    I feel compelled, though, to point out that the ESS often starts out with more than 400 V, so your 375 V figure probably doesn't need to be reduced by 10%. Granted, when you floor it that potential of 425 V drops to as little as 325 V, but my point is that it's really difficult to make a precise conversion from amperes to anything else.

    According to Tesla Motors, torque is directly proportional to the angle of the AC waveforms that are sent to the motor. The target torque is set by the position of the accelerator pedal, but I don't know if there is a direct correlation between torque and current. Maybe I'll just have to look for some flat areas in the VehicleLogs graph to see whether there are any hard torque limits in these modes (at least the ones like Valet Mode that are easy to select).
     

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