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Quantifying the Volt MPG

Discussion in 'Electric Vehicles' started by malcolm, Sep 7, 2008.

  1. malcolm

    malcolm Active Member

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  2. vfx

    vfx Well-Known Member

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    #2 vfx, Sep 7, 2008
    Last edited: Sep 7, 2008
    I agree on the clarity of 40 E miles, then 48 MPG

    Perhaps use that in the big bold print with a bottom-of-the-page chart that talks about Watts per mile.
     
  3. Joseph

    Joseph Member

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    Here is what I posted at ABG

    "The EPA rated an EV's mpg by mpg equivilant. Do the same for cars like the Volt; you just need to add the gallons of gasoline used to the "gallons" of gasoline equivilant used.

    So, the Volt uses something like 10 kwh for a 40 mile journey. Since a gallon of gasoline holds the equivilant to about 33kwh, that means the Volt used about a third of a "gallon" to travel forty miles.

    That means it gets around 120 miles per "gallon."

    Now, (according to the information provided in this blog post) the EPA test is 46 miles, leaving 6 miles not in EV mode.

    Let's suppose that the car gets 50mpg in this mode. That would mean that 85% of the test is 120mpg and 15% of the test is 50mpg.

    For the first forty miles you would use 1/3 a gallon of "gasoline" and .12 gallons of actual gasoline for the remaining six miles. So....forty six miles and .45 gallons of gas.

    That comes up to the grand total of 102 miles per gallons equivilant.

    So, assuming my math is correct, the EPA rating for the Volt (in my opinion) should look something like this:

    FULLY CHARGED

    City: xxx mpg equivilant

    Highway: xxx mpg equivilant

    Combined: 102 mpg equivilant

    EMPTY/HYBRID MODE

    City: xx mpg

    Highway: xx mpg

    Combined: 48 mpg"

    The EPA also used watt-hours per mile as way of measuring an EVs consumption, but I think that mpg equivilant is much better because that gives the consumer a much better feel for just how efficient an EV is. A gasoline vehicle's mpg is essentially energy consumed (x gallons) over miles (x miles) therefore x miles per gallon. For an EV (or PHEV in this case) it should be no different. You just need to convert the electrcity into "gallons."
     
  4. doug

    doug Administrator / Head Moderator

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    #4 doug, Sep 7, 2008
    Last edited: Sep 7, 2008
  5. stopcrazypp

    stopcrazypp Well-Known Member

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    I agree, all that is needed is kWh/100miles for the EV mode (as it is done on other EVs) and the mpg for the hybrid mode. The EV range should also be included. That is basically all the information you need to do all the calculations you want. MPGe is only for CAFE considerations. With PHEVs, MPGe is just too convoluted because it changes so much depending on how many electric only miles you travel compared to the gasoline miles.
     
  6. Joseph

    Joseph Member

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    How about both then? The sticker can tell you:

    1. mpg equivilant fully charged

    2. wh/mile fully charged

    2. mpg not charged

    The only problem might be that it is too confusing. Then again, a car window sticker already includes alot of information, so it shouldn't matter.
     
  7. malcolm

    malcolm Active Member

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    Well it's safe to assume that some auto marketeers will choose to promote the figures which make the boldest claims. So we can expect a variety of misleading numbers come 2010/11.

    It was interesting to note that Tesla aren't doing this. In the recent Fifth Gear TV test drive, Vicki Butler Hederson quoted the old 135 mpg number rather than the inflated/legislated 256 figure.

    I hope they can maintain this.
     
  8. vfx

    vfx Well-Known Member

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    Knowing our Government, I'm betting the final numbers will be confusing...
     
  9. Kardax

    Kardax Member

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    I think Volt-like vehicles should get 2 numbers:

    City Electric Range
    Highway MPG

    That provides the most meaning to potential customers, as it represents the most likely scenarios where each mode would activate.

    -Ryan
     
  10. malcolm

    malcolm Active Member

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    #11 malcolm, Sep 11, 2008
    Last edited: Sep 11, 2008
  11. vfx

    vfx Well-Known Member

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    #13 vfx, Sep 25, 2008
    Last edited: Sep 25, 2008
    Another thing the writers and commenters to date missed was that this system is better for the batteries. Less cycling (charging depleting -repeat) means longer life.


    edit: Ok I did.
     
  12. vfx

    vfx Well-Known Member

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    #14 vfx, Sep 26, 2008
    Last edited by a moderator: Sep 26, 2008
    Over at Martin's blog Chris wrote and Martin responded:

     
  13. Cobos

    Cobos S60 owner since 2013

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    Huh ? I fail to see how this "change" is a problem? They will make sure you can plug it in as much as possible and that you will spend the least amount of gas. How can this be a problem? It's still an EV. It either works as a pure BEV for the first 40 miles and then works similar to a diesel-electric train driveline. Though in this case for the Volt as a E85/gas-electric instead. This sounds like the GOOD option if the other one was burning more gasoline through the generator arriving at home with a 100% battery. If my commute each day is a total of 60 miles I want to make sure I recharge during the night and then the last 20 miles on the way home the generator kicks in. It just uses enough fuel for me to get me home and recharge again for cheap electric driving from the grid.

    Cobos
     
  14. doug

    doug Administrator / Head Moderator

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    What?? So even Chris and Martin are confused by this? They probably just didn't spend the time to read behind the reporter sensationalism.

    From what I can glean from these stories, GM is designing the Volt to do exactly what it should. These reporters are not engineers. They have it stuck in their heads how standard (Prius type, non plug-in, parallel) hybrids work, and they think that's the way it should work. Maybe there is something to this "E-REV" nomenclature, since the public seems to think there's only one way a "hybrid" should work.

    Edmunds suggests that after that first 40 miles, the Volt's battery is useless -- 400 lbs of dead weight. That's ridiculous. They seem to forget the Volt's battery is only allowed to charge as high as 80% and discharge to 30%. So after you're down to 30% the generator kicks in, keeps you going on the road and and maintains the battery to 30%. That means it uses some battery power when needed (e.g. hill climbing, hard acceleration) and puts some energy back into the battery during regen. When you get home, you get another 40 miles from the grid, not from your gas tank. This is how a plug-in serial hybrid should work.

    Have to say that this sort of thing kind of annoys me. Sensationalistic headline about some recently discovered "drawback." It's just like the "Tesla Roadster Will Take 30 Hours to Charge, OMG!!!" headlines from a while back. The real story is the reporters' lack of understanding, not what's in the article.
     
  15. TEG

    TEG TMC Moderator

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    I'm with Doug, but I am trying to stay away from all the Volt debates in general.
     
  16. doug

    doug Administrator / Head Moderator

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    Looks like Autoblog is on top of it. I sent them a message asking them to do an article to straighten this mess out. I got permission to post the editor's response to me:
    Here's IL's followup article which attempts to clarify, but spins their misunderstanding as a GM reversal.
    As the Volt Turns: GM Exec Says Battery Will Recharge While Driving

    And here's the Autoblog article:
    Settle down: Volt batteries can recharge while driving - Autoblog

    But now we're back to the original topic of this thread. How are they calculating 100mpg?
     
  17. malcolm

    malcolm Active Member

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    #19 malcolm, Sep 26, 2008
    Last edited: Sep 26, 2008
    GM-VOLT : Chevy Volt Electric Car Site Blog Archive Latest Chevy Volt Battery Pack and Generator Details and Clarifications

    So now there's a bit more omph in the generator to recharge the pack, but we don't know by how much.

    It may be that normal driving produces the same effect as was originally reported above.

    "Your mileage may vary" becomes "Your recharge rate may vary"

    I think Martin is right. If they implement this then driving habits as well as regen will vary recharging far more widely than the predictable rate available from the garage wall socket. They will be stressing the batteries.

    I'm guessing they'll wait for the fuss to die down then revert to Plan A.
     
  18. stopcrazypp

    stopcrazypp Well-Known Member

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    I think this kind of confusion is brought very early on by GM's own insistance that this car be called an E-REV instead of a plug-in series hybrid and then repeating that the generator will only charge the batteries (or implying that) in order to affirm the point it should be called an E-REV and not a hybrid.

    I remember early on there were a bunch of people getting up in arms that this car isn't a series hybrid because the electricity from the generator isn't directly powering the motor, but I knew this would have to happen for this car to remain efficient and not to wear out the batteries.
     

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