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EPA rates Model S at 89MPGe with 85 kWh pack

Discussion in 'Model S: Battery & Charging' started by Discoducky, Jun 20, 2012.

  1. Norbert

    Norbert TSLA will win

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    Doe anyone know whether the Leaf's 73 EPA mile range is achieved with putting some battery capacity aside, as reserve, and only using perhaps 21 kWh or so, or if it is achieved with the full 24 kWh, also using the reserve ?
     
  2. Tommy

    Tommy Member

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    Thanks, that was info I wasn't aware of. Currently, it looks like any additional improvements in the mpg-e will likely come from efficiency gains Elon's hinted at with the on-board Model S charger(s)
     
  3. SoCalGuy

    SoCalGuy Active Member

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    I don't think that's correct - it should be apples to apples on the basis of the equivalent math above. The Fisker numbers are very close (3-5%), and the delta is within rounding errors. The Model S nums seem off by20% .
     
  4. Dave EV

    Dave EV Active Member

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    The usable capacity of the Nissan LEAF is around 21 kWh. The EPA test procedures dictate that the car be charged to 100% and run through the test until the car is unable to go fast enough to run through the load profile. It takes around 24-25 kWh from the wall on L2 240V/16A to charge the LEAF from turtle mode to 100%.
     
  5. stopcrazypp

    stopcrazypp Well-Known Member

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    #45 stopcrazypp, Jun 21, 2012
    Last edited: Jun 21, 2012
    The numbers will vary based on how much actual usable capacity the car has and also the charging efficiency. The established EPA procedure is to measure electricity used at the socket. If the usable capacity percentage is the same as the charging efficiency percentage, the result will be like the Fisker's numbers.
    http://www.smidgeindustriesltd.com/leaf/EPA/EPA_test_procedure_for_EVs-PHEVs-1-13-2011.pdf

    The 2013 Volt gets 35kWh/100miles. AER is 38 miles. Works out to 13.3kWh to fully charge. 10.8kWh usable. 81.2% charging efficiency.
    http://www.thedetroitbureau.com/wp-content/uploads/2012/06/2013-Chevrolet-Volt-window-sticker.jpg

    The 2012 Leaf gets 34kWh/100miles. AER is 73 miles. Works out to 24.82kWh to charge. 21kWh usable. 84.6% charging efficiency.
    http://www.hypermiler.co.uk/wp-content/uploads/2011/01/nissan-leaf-epa-sticker-photo.jpg

    The Fisker gets 65kWh/100miles. AER is 32 miles. Works out to 20.8kWh to charge. 18kWh usable (found the link below). 86.5% charging efficiency. As I said, the actual capacity is 20.1, so 89.6% usage (similar to the charging efficiency) which makes the math seem to work out (but not quite).
    http://www.thecarconnection.com/review/1073134_2012-fisker-karma_green_7
     
  6. jimbakker666

    jimbakker666 Member

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    I don't understand how this is allowed to occur. It takes two seconds to look at Tesla's website and see that the base car price this writer is quoting is wrong. It seems more blatant lie than casual oversight and it really annoys me that this guy isn't checking his facts.

    Interested to see if Tesla can make the charging scheme more efficient. My money says yes.
     
  7. richkae

    richkae VIN587

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    265 miles per 85kWh battery suggests 32kWh per 100 miles actual performance.
    Wall to wheel 38kWh per 100 miles means 84% efficient charging.
    Increasing charging efficiency to 91% gets you 35kWh per 100 miles and bumps you to 97mpge from 89.
     
  8. Todd Burch

    Todd Burch Voltage makes me tingle.

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    Source: Detroit. I don't think it's coincidence that seemingly every "fact" coming out of a Detroit source is wrong, and wrong in a way that casts a negative light on the Model S and Tesla. Some may see my view as cynical...I see it as reality. With the exception of smaller Detroit suppliers providing parts for Tesla, Detroit has every incentive to quell interest in that Silicon Valley company that seems to have developed a high tech vehicle and full manufacturing facility for a fraction of the cost of the big guys.
     
  9. malcolm

    malcolm Active Member

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    #49 malcolm, Jun 21, 2012
    Last edited: Jun 22, 2012
    The biggest factor affecting overall charging efficiency isn't the few percentage points you can squeeze out of the power electronics, it's the overall losses including things like battery cooling. (Is this the reason that the Leaf's figures are better?)

    The EPA should make it clear that electricity use also varies with charging power, so that the table would hold (say) eight numbers rather than just four. For example:




















    Wall Socket Recharging Power kW City MPGe Highway MPGe Combined MPGe Cost Saving $
    2
    10
    Maybe Tesla can publish something like this in the Model S brochure/manual? They could highlight the row which features the official EPA numbers.
     
  10. Norbert

    Norbert TSLA will win

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  11. SoCalGuy

    SoCalGuy Active Member

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    Thanks - helpful. When you talk about 'charging efficiency' are you suggesting that there's energy loss between the wall socket and the car's battery i.e. as heat in the cable/plug/onboard charger? I know that each of these cars has a electric unusable reserve amount in the battery to preserve battery life/longevity and prevent bricking (Fisker's is 15%, so the actual A123 battery is 23 kwh but only 20kwh or so is usuable). That said, I would still presume that only the usable amount matters in the MPGe calc since its not like at every 'fill up' you need to replenish this reserve (since its not depleted by the vehicle).
     
  12. Norbert

    Norbert TSLA will win

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    The EPA's calculations seem independent of the battery size (used or unused)... they supply a full charge, drive it until it can't hold the required speed anymore, and measure how many kWh are required to re-charge it from there to full (until it stops charging).
     
  13. stopcrazypp

    stopcrazypp Well-Known Member

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    Got the number from the Leaf forum (it was measured by one of the members):
    http://www.mynissanleaf.com/wiki/index.php?title=Battery,_Charging_System#cite_note-5

    At no point does the EPA procedure measure or report the "usable" capacity (it does report the full capacity of the battery), so this data must be taken from the manufacturer or measured by an end user.
     
  14. stopcrazypp

    stopcrazypp Well-Known Member

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    #54 stopcrazypp, Jun 22, 2012
    Last edited: Jun 22, 2012
    You are correct that the energy is lost as heat in the cable/plug/onboard charger. There's minimal loss from the cable and plug; most of it is from the onboard charger converting 120V or 240V AC electricity from the socket to ~400V DC electricity to charge the battery. The battery also heats up during charging and energy is lost there too. That's why proper ventilation while charging may be necessary if your garage temperatures are high. There's also some loss when drawing electricity from the battery, but that's minimal also.

    From the article I link, it appears the production Fisker Karma has a 20.1kWh pack, with 18kWh usable; the 23kWh number was from the pre-production Karma:
    http://www.thecarconnection.com/review/1073134_2012-fisker-karma_green_7
     
  15. Norbert

    Norbert TSLA will win

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    AFAIK, the Model S and Roadster additionally use battery cooling during charging, which also requires energy.
     
  16. stopcrazypp

    stopcrazypp Well-Known Member

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    That's true, I added the part about the battery heating up during charging (which is actually a very significant loss besides from the charger conversion loss). For liquid cooled batteries (doesn't apply to Leaf), yes battery cooling also requires additional energy.
     
  17. malcolm

    malcolm Active Member

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    #57 malcolm, Jun 22, 2012
    Last edited: Jun 22, 2012
    Thanks, so all Tesla need to do is publish a "Your charging may also vary your milage" section in online and hard-copy documents.

    Ultimately the EPA 5 step test needs to include a standard for recharging (e.g all electric vehicles which can be recharged from a wall socket are recharged at "X" kW)

    Then EV manufacturers can optimise their charging systems to get the best results from the test - just like all vehicle makers optimise cars to improve City or Highway test figures.
     
  18. Dave EV

    Dave EV Active Member

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    Yep - at a minimum it would be nice if the EPA tests at least reported what charge rate was used to get the economy numbers. Ideally, we'd get numbers for a few different common charge rates.
     

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