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Battery usage due to two motors

Discussion in 'Model X' started by Merrill, Jun 7, 2014.

  1. Merrill

    Merrill Active Member

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    Does the model x use more battery because it has two motors? Will it have higher watts per mile than the model s.
     
  2. dsm363

    dsm363 Roadster + Sig Model S

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    Just a guess but it will likely be heavier and less aerodynamic than the Model S so might have worse Wh/mile. Of course they have had an extra three years of development on platform so maybe thy counteracted those factors.
     
  3. haid

    haid Member

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    My understanding is that Tesla intends to have different gear ratios on each motor. This would allow them to favor power to one pair of wheels at lower speeds and the other at higher. Potentially this could be more efficient and allow a higher top speed.
     
  4. yobigd20

    yobigd20 Well-Known Member

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    per one of the EU Q&A sessions, Elon and JB said Tesla was able to create a breakthrough enhancement by finding some clever ways with dual motor AWD, not just mechanical linkage, to make the Model X's AWD flat efficiency tradeoff aka identical Wh/mi as the MS even through it is a bit bigger and slightly less aerodynamic. no other ICE vehicle has ever achieved a flat efficiency tradeoff for an AWD option so this so just another +1 to incredible Tesla achievements.
     
  5. Merrill

    Merrill Active Member

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    Thanks Yobigd, that would be amazing and a real plus if it is similar to the Model S.
     
  6. MartinAustin

    MartinAustin Active Member

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    To answer the original poster's question, there ought to be no significant difference in battery life when using two motors. Let's think it through:

    If you are in a current Model S, taking (say) 200kW of power out of the battery, you are putting 200kW into your lone motor, and 100kW down onto the road through each rear wheel. The front wheels just follow along for the ride with virtually no wear and tear, but the rear wheels get a beating. Hello Traction Control!

    If you are in a Model X with dual motors, and are taking that same 200kW out of the battery, you are putting an average of 100kW into each motor, and an average of 50kW down onto the road through each of your four tyres. So your equipment is less stressed than in the Model X. You have four places where you are getting traction, so Traction Control won't step in as much, and your tyres last longer (read: more miles travelled between sets of tyres)

    The only downside is that the dual motor arrangement weighs more than the single motor arrangement. How much heavier? Perhaps 200lbs? You will therefore get worse mileage than an equivalent one-motor car, because you're lugging around 200lbs more. That is offset by better/smoother traction and longer tyre life IMO but may result in slightly worse battery life on an equivalent car due to the 200lbs.

    The fact that the Model X intrinsically weighs more/has worse aerodynamics than the Model S, because it's physically bigger, is unavoidable.

    I personally can't wait to drive an AWD Model S.
     
  7. stopcrazypp

    stopcrazypp Well-Known Member

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    The AWD option might be able to be designed to be the same efficiency as the RWD, but the Model X's worse aerodynamics and heavier weight will have to be dealt with. I think if Tesla successfully lobbies some changes with the NHTSA about removing side mirrors, they can make up the difference.
     
  8. de704

    de704 XP268

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    There's over 7000 "18650 cells" I don't see any problem with a portion being used for each motor. Also remember the motors are not equal in power. The front motor is smaller.
     
  9. Ampster

    Ampster Member

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    If you are implying that the pack will be divided between motors, that does not make sense. The amperage will be divided.
     
  10. MarkR

    MarkR Member

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    I think there is little doubt that side-mounted mirrors are on there way out because most manufacturers see them as grossly out of step with today's technology and the need for greater fuel efficiency will demand cars with lower drag coefficients. With that being said, I still highly doubt that the MX can match the mileage of the MS even with other improvements in technology. The MX is just too much bigger, heavier, and has the additional power requirements of the falcon doors.
     
  11. de704

    de704 XP268

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    It's a known fact that the Model S doesn't use the same cells each time you drive (on shorter drives of course). It does this to extend the life of the battery as a whole. This "implies" that Tesla has granular control over the battery pack. Following this line of thinking, I'm saying they can most likely deliver full power to each motor simultaneously using different cell "if they choose to".

    But there are also video's on the web where a Model X engineer/designer states that the front (smaller) motor is optimized for highway driving and the rear motor is optimized for acceleration and that even though there is two motors this doesn't necessarily mean that more power is used.

    It's been out there for years ;)
     
  12. stopcrazypp

    stopcrazypp Well-Known Member

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    [citation needed]

    The Model S needs to use all the cells in the pack to be able to provide the full voltage of the battery pack, which is then converted to AC by an inverter. This is because the modules are wired in series, not in parallel (as some may have thought). The only way it can use partial amount of cells is if it can manually/electronically disconnect parallel connections between cells, but looking at the pack opened up we already know that is not possible.

    What varies during driving is the amount of current that is pulled from the cells (and the pack voltage naturally going to down). Like what Ampster said, what is split is the current (by the power electronics), not the actual battery pack.

    The closest think to your idea is that the Roadster had a special "sheet" in the battery that was used primarily for 12V power, but they dropped that in later versions.
     
  13. Nubo

    Nubo Test Mule

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    Even though they have very wide power bands, electric motors can still be optimized for a certain range of rpm and torque. So, the ECM could to some degree preferentially use the "highway" motor or the "city motor" based on conditions. I.e., the front-rear power ratio could be variable, taking into account not just traction but efficiency.
     

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