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Electric cars

Discussion in 'Electronic Design' started by Michael, Jan 27, 2009.

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  1. Michael

    Michael Guest

    This is what has been bugging me.
    Imagine a family with two electric cars. 100HP (75kW) engine each -
    not too big, is it? On an average workday each driver commutes for on
    hour (lucky guys, aren't they?).
    It makes 150KWh energy needed to recharge the cars.
    Assume 10 hours (overnight) charge. It means 15kW of power (minimum)
    is delivered to the house.
    Do we have an infrastructure to support it?
    Am I missing something?
     
  2. On average, a car needs nowhere near 75kW. Some 10 to 15kW
    should do fine. Even so, you are right to believe that the
    current infrastructure wouldn't suffice if everyone used
    electric cars.

    Jeroen Belleman
     
  3. Bob Eld

    Bob Eld Guest

    Answer, NO. We do NOT have an infrastructure to support electric cars. Keep
    in mind that an auto engine or motor, electric or gas uses a small fraction
    of its available power most of the time. Therefore the problem is not as bad
    as you propose.

    Another issue is that 1/2 of the electricity generated in the US comes from
    burning COAL. What is the point of eliminating convenient liquid fuels and
    replacing them with the dirtiest fuel available and hooking up to that fuel
    with expensive 400 mile long extension cords?

    Electric cars make little sense until the electricity itself is green or
    nuclear, non polluting.
     
  4. Michael

    Michael Guest

    You are probably right, but keep in mind that most of the people (at
    least current driving generations) won't accept that. It will take
    years and years and years (generations) to change this redneck my-
    truck-must-be-bigger-than-your-truck attitude. :eek:(
     
  5. There might be a hidden benefit to having large numbers of electric
    cars. Nuclear plants run best @100% and storage of energy is a
    potentially huge cost. Other generation methods have similar
    limitations (eg. solar is only available when the sun is shining)
    unless they involve burning of fossil fuels. Having millions of high-
    capacity batteries paid for by consumers might not be such a bad
    thing. Those willing to load- level the grid (including the option to
    supply energy back into the grid) could get big discounts on the net
    cost of the energy they use. Most cars sit in a parking lot 90% or
    more of the time, so they'd be available for such duty.
     
  6. Eeyore

    Eeyore Guest

    NO, you've found one of the fatal flaws although your numbers are a
    little oversimplified.

    NO-ONE NEEDS 200 hp to commute to work and before long the option's
    unlikely to be available to them either through legislation, taxation or
    the simple price/availability of fuel. Average WORLD car engines average
    < 100 hp.

    I suggest you also look at how long batteries last. Plus the miserable
    efficiency of average electric power generation. 'New generation' diesels
    @ 40% are going to look very attractive.

    Electrolytically produced hydrogen is even more laughably inefficient.

    Graham
     
  7. Eeyore

    Eeyore Guest

    That's as idiotic as 200hp ! 0 - 60 in one minute maybe ?

    Graham
     
  8. Eeyore

    Eeyore Guest

    And thereby hangs the problem of the USA. Everything must be HUGE to impress
    since you have no concept of asthetics or subtelty.

    Not a problem for the rest of the world of course. We can get on fine without
    you. Better in fact without all those US inspired resource and life sapping
    wars you love so much.

    Graham
     
  9. krw

    krw Guest

    Have you looked in a mirror (either figuratively or literally)
    lately?
    Not to worry, you Europeons will be at each other's throat again
    soon.
     
  10. Charlie E.

    Charlie E. Guest

    But, of course, not everyone will buy an electric car immediately when
    they become available. As more and more cars come on line, then the
    electric company will be doing some dancing to put in all the
    additional service throughout all the towns and cities to support the
    additional demand

    Either that, or solar chargers of some sort will become extremely
    popular... :cool:

    Charlie
     
  11. nospam

    nospam Guest

    How much of your car battery capacity would you be willing to sacrifice to
    load level the grid?

    If you are prepared to sacrifice a significant amount what is the point
    lugging a heavy half empty battery around the country with you? Why not
    have a smaller battery to start with?

    What does a daily (twice daily?) charge/discharge cycle do for the already
    short life of lithium batteries?
    --
     
  12. Eeyore

    Eeyore Guest

    And the total efficiency of all this extra generated electricity from power
    station fuel input to vehicle drive train is ??? Compared to say 40% for new
    generation diesels for example ?

    I can tell you it won't look very impressive, plus think of all the
    batteries you'll have to replace.

    Have you seen the price of solar cells ? Plus there's not much sun at night.
    Fear not, mere politically incorrect inconveniences.

    Graham
     
  13. Eeyore

    Eeyore Guest

    mass = 2.5 tonne SUV. power in = 75kW

    In 10 secs energy delivered = 750kJ

    Energy = 1/2 mass.v^2

    v^2 = 2 (Energy/mass) = 2(750kJ/2500) = 600

    v = 24,5 ms-1 = 88 kph = 55 mph

    So almost. But your motor and battery has to be rated for 75kW. Now try
    uphill !

    About 20kW for US size vehicles.

    Graham
     
  14. Eeyore

    Eeyore Guest

    What on earth makes you think that ? How about another US Mexico war ?

    Graham
     
  15. Eeyore

    Eeyore Guest

    Depends on the depth of discharge.

    Graham
     
  16. Ecnerwal

    Ecnerwal Guest

    Well, they'd have to redesign the car to make the battery "pack" at all
    economical to replace in the first place. It's not exactly a cordless
    tool, swap the pack deal, and the "pack" alone costs more than most used
    cars. Only one or two states require that it keep working for a
    reasonable period of time - anywhere else, it dies, you have a humongous
    repair bill, or a dead (yet pretty) car.

    Thing being, a Honda Civic hatchback gets nearly the same milage, did so
    years before the Prius came out, and isn't dead with no economically
    sensible repair at 10 years (if you actually get 10 years).

    The current crop of hybrids are a car maker's dream, as they will need
    utterly nonsensical repair bills to ever become old cars, so they'll be
    run off to the junkyard at an early age.
     
  17. James Arthur

    James Arthur Guest

    So the premise is Joe Average burns 13kWHr driving to work,
    the grid taps him for another 15kWHr while at work, he burns
    12kWHr driving home, then refills 40kWHr overnight.

    But plug-in hybrids' premise/promise is to use most or all of
    their charge on the way to work, recharge, then drive home.

    GM's 'Volt' goes up to 40 miles on its 16kWHr pack before
    cranking up its ICE. And that costs $40k.

    So when he gets to work, Joe's battery is empty, thirsty for
    juice.


    As a first step to ultraefficiency, superlight, streamlined cars
    make sense. Add serial hybrid drivetrains if you want to go the
    extra mile.

    (Amory Lovins says 2/3rds fuel savings is possible for
    about $0.15/liter.)


    Better to use less energy to start with than to figure out
    better bleeding edge new ways to juggle and keep using
    the same amount.

    Cheers,
    James Arthur
     
  18. Yes, nuclear would solve a lot of problems, like CO2 and "dependence on
    foreign oil".

    The REAL problem is, how do we get this information through the thick
    skulls of the paranoid bureaucrats?

    Thanks,
    Rich
     
  19. James Arthur

    James Arthur Guest

    Parallel hybrids in conventional bodies don't really do
    much better than my Acura--Mom's Civic Hybrid gets about
    44mpg, I get about 41mpg. The hybrids /are/ more efficient,
    but her car's heavier and more powerful. It needn't be
    either.

    The 2009 Nissan Altima Hybrid rates 35mpg and has a 158hp
    2.5L gas engine.

    Sheesh. That should be 40hp electric, plus a 20hp ICE for
    recharging. Much more efficient, lighter, AND faster. A
    lighter car doesn't need as big an engine to be fast. Easier
    to make. Lighter=less materials used, cheaper, less waste, etc.


    James Arthur
     
  20. James Arthur

    James Arthur Guest

    Put windmills on top of the cars & they'll recharge themselves on
    their way to work. And painting them green will provide more green
    jobs too, saving the planet and the economy. Win-win.

    Cheers,
    James Arthur
     
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