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Big Battery Means Big Range, Cost for Tesla's Model S

Discussion in 'News' started by Doug_G, Jul 13, 2012.

  1. Doug_G

    Doug_G Lead Moderator

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    Design News - Big Battery Means Big Range, Cost for Tesla's Model S

     
  2. brianman

    brianman Burrito Founder

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    My mental model has a hole / disconnect on a related topic, so maybe someone can help me out.

    Yet the EPA MPGe rating is in the other direction. I'm aware the wall-to-battery efficiency comes into play, but I'm surprised it causes the position flip.


    Carrying the train a thought a little further...
    If the Volt or the Leaf replaced structural components (i.e. ignore safety considerations) and sacrificed passenger space (i.e. ignore convenience and utility of the vehicle) to switch to an 85 kWH Tesla battery, would they get longer range than the Model S?
     
  3. gocken2

    gocken2 Model S: P6931

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    I believe the low EPA MPGe on the Tesla is due to the car using power to condition the battery pack while charging. It's the charging efficiency where the Leaf comes out ahead not distance per KWh.
     
  4. ahimberg

    ahimberg Member

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    you're mixing numbers? to compare the 85kWh to Leaf's 24KWh, are you comparing the 300 range to 100 range of leaf, or the EPA numbers of 265 & 73? Leaf is still ahead but not by much.
    as for the 60kWh, 40kWh, we don't know EPA numbers, if they scaled exactly we'd have 140 EPA for the 40kWh?
     
  5. brianman

    brianman Burrito Founder

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    Is the conditioning throughout the full 0 - 100% SOC transition or does it vary? If it varies, this suggests a crudeness in the EPA calculations.

    For example, if charging from 20% - 30% has a lower "from wall" efficiency than 60-70% then one could argue that for "daily driver, limited miles" the efficiency calculation is way off. It sounds a lot like the difference between city and highway MPG differences in traditional (ICE) efficiency measurement.

    Also, if the conditioning varies across SOC -- at least for the Tesla chemistry/chemistries -- there may also be missing aspect related to battery size. I would expect a "5 Wh" battery has far better "wall efficiency" than any "5 kWh", because you could simply choose a chemistry for the "5 Wh" where you are well below the actual charge that can be retained (and also not need any conditioning). Furthermore, you could "overfill" it with regen so that for the EPA test it has infinity MPGe (because it didn't lose charge below the 5 Wh threshold) -- as long as you don't run the test multiple times in a row.




    I guess what I might be getting at is that either -a- Tesla is behind on wall efficiency or -b- the EPA measurement / analysis isn't sophisticated enough to tell the story. If the former, I'm curious to hear more about it.

    I would argue a significant portion of the population will just compare the MPGe number somewhat blindly, like for MPG.


    Anyway, the forum's relatively quiet so I figured I'd carve out some time to learn. :wink:
     
  6. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    In the Roadster it's been determined that the most efficient charge is done at 40 amps. Below 40 and there are higher line losses (as I understand it), above 40 and the cooling fans have to engage more. Until someone measures we won't know what the best charge rate is for the Model S. I'm not sure what rate the EPA charges at. If it's 30 amps (which would make a certain amount of sense because the L and V charge at those rates) and the Tesla behaves like the Roadster (an unknown right now) then the EPA charge rate is non-optimum.
     

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