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Electric cars

Discussion in 'Electrical Engineering' started by metspitzer, Jun 15, 2008.

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  1. metspitzer

    metspitzer Guest

    Every time the price of gasoline goes up a penny it costs the US
    Postal Service $8 million

    http://www.foxnews.com/story/0,2933,367187,00.html

    }

    It is my understanding that stop and go driving is what electric cars
    do best. I would think the post office would be the best candidate
    for electric cars, at least in heavy populated areas.
     
  2. bud--

    bud-- Guest

    But with an electric car you can use the motor as a generator and do
    regenerative braking converting most of the kinetic energy back to
    electrical energy in the battery. In a conventional car the kinetic
    energy is lost as heat in the brakes.
     
  3. James Sweet

    James Sweet Guest


    That's true of any vehicle, if you have a lot of stops, an electric
    vehicle should have advantages in that the engine doesn't need to idle
    while the vehicle is stopped.
     
  4. Guest

    |
    | pat wrote:
    |> high volume stop starts are energy wasteful, overall efficiency drops
    |> rapidly the more an electric vehicle has to stop and start.....electric is
    |> best on long straight runs even more so if this includes batteries.
    |>
    |
    |
    | That's true of any vehicle, if you have a lot of stops, an electric
    | vehicle should have advantages in that the engine doesn't need to idle
    | while the vehicle is stopped.

    That and the brakes can return most of that energy back to the batteries.
     
  5. James Sweet

    James Sweet Guest


    In theory, yes, in practice, I don't know how much actually makes it
    back into the batteries. I suspect dynamic braking is much more
    effective in long steady braking such as descent down a long hill than
    in small, low speed stops. I have no data to back this up though and
    would be curious to see real world measurements.
     
  6. James Sweet

    James Sweet Guest


    Where does it get to 50 below?

    Certainly in most of the populated areas of North America the
    temperature range would not be an issue.
     
  7. metspitzer

    metspitzer Guest

    Don't use them at those temperatures.
     
  8. Don Kelly

    Don Kelly Guest

    ----------------------------
    Fairbanks, Alaska it gets 50 below in the winter and has freezing
    temperatures for six months out of the year. We use electric battery
    blankets, head bolt and transmission heaters in the winter. It used
    to cost about $100 a month to plug in a car from October to March, but
    that cost has risen by about 50 percent. Battery powered cars are out
    of the question here. The same applies to solar power and wind
    power. There are about 100,000 people living noth of the 63 meridian
    that have this problem in Alaska.


    ----------------

    Do you use in hose water heaters? - I have found these to be more effective
    than the typical block heater in that they set up a natural convection of
    "hot" water. While having only occasional experience of -50, I remember
    many -40 days in Alberta, Manitoba and Quebec. Now, on Vancouver Island, it
    is much balmier so these memories do fade. Through places like Juneau and
    Ketchican, electric cars would work and as there isn't far that you can
    drive there-they might do quite well.
     
  9. James Sweet

    James Sweet Guest


    That's a pretty tiny minority of the population really, and a special
    case for sure. With a population of over 300 million, 100k is but a drop
    in the bucket, and I'll stand by my assertion that for the vast majority
    of the population, the temperature is not an issue. Obviously not
    everyone everywhere could get by with an electric vehicle, but the same
    can be said of any type of vehicle.
     
  10. bud--

    bud-- Guest

    The only hybrid I have looked at is a Prius. It is rated 48 mpg city, 45
    highway - the regenerative braking must be pretty good. The brakes are
    smaller than they would be on a 'normal' car. If you stop too fast, less
    energy is captured. (Driving stupidly in a 'normal' car lowers gas
    mileage too.) On very long descents you can capture more energy than the
    battery capacity. For that there is a mode that runs the engine for
    compression braking.
     
  11. James Sweet

    James Sweet Guest


    For all the cool technology it contains, I'm afraid I'm just not
    impressed by the Prius. When I was a kid, my parents had a Mercury Topaz
    diesel that got 55-60 mpg, and that was 25 years ago. 100 mpg would
    pique my interest, but 45-50 is old hat, even with current fuel prices
    it's more economical to drive a conventional car and not have the
    complexity of two powerplants, batteries, computers, etc. I suspect
    these things will be a nightmare when they reach 10 or so years old and
    the batteries are failing.
     
  12. daestrom

    daestrom Guest

    While not Fairbanks, we often get temperatures in the mornings that
    are -10F. New York isn't known for its cold weather, like some other
    states, but I wonder how the batteries would fair at -10F in the morning.

    daestrom
     
  13. daestrom

    daestrom Guest

    Growing up in Michigan, I can attest that it gets colder here in NY.
    Michigan has the Great Lakes to help moderate the temperatures of any artic
    air coming down from Canada. International Falls, Minnesota is often in the
    news as a cold place. And here in New York we see -10F to -20F a few times
    each winter.

    daestrom
     
  14. krw

    krw Guest

    Something like C/2 for every -10C, no? So range gets to be a
    serious problem in the winter for much of the US. BTW, I lived in
    NW VT for 15 years. Most years there are a couple of weeks were the
    lows are in the -20F range and the highs 0F, or below. Not a good
    place for batteries, though never froze one like my brother in
    Minneapolis did.
     
  15. James Sweet

    James Sweet Guest


    How about the numbers for NiMH? I don't think lead-acid is a serious
    contender for electric cars anymore. If the prices of Li-Ion would drop,
    performance and range could approach that of gasoline cars.
     
  16. Guest

    | Gerald Newton wrote:
    |>>> Fairbanks, Alaska it gets 50 below in the winter and has freezing
    |>>> temperatures for six months out of the year. We use electric battery
    |>>> blankets, head bolt and transmission heaters in the winter. It used
    |>>> to cost about $100 a month to plug in a car from October to March,
    |>>> but that cost has risen by about 50 percent. Battery powered cars
    |>>> are out of the question here. The same applies to solar power and
    |>>> wind
    |>>> power. There are about 100,000 people living noth of the 63 meridian
    |>>> that have this problem in Alaska.
    |>>
    |>>> ----------------
    |>>
    |>> That's a pretty tiny minority of the population really, and a special
    |>> case for sure. With a population of over 300 million, 100k is but a
    |>> drop in the bucket, and I'll stand by my assertion that for the vast
    |>> majority of the population, the temperature is not an issue.
    |>> Obviously not everyone everywhere could get by with an electric
    |>> vehicle, but the same can be said of any type of vehicle.
    |>
    |> I think there are other northern states where batteries would be a
    |> problem including Montana, Minnesota, North Dakota, Michigan and
    |> Wisconsin.
    |> For these new hybrid cars to be accepted they will have to operate in
    |> freezing temperaures of at least 20 degrees F below zero.
    |
    | Growing up in Michigan, I can attest that it gets colder here in NY.
    | Michigan has the Great Lakes to help moderate the temperatures of any artic
    | air coming down from Canada. International Falls, Minnesota is often in the
    | news as a cold place. And here in New York we see -10F to -20F a few times
    | each winter.

    I understand that they are doing a lot of alternative electric cars in
    Iceland these days, due to the cheaper hydrothermal energy sources.
     
  17. krw

    krw Guest

    I'm sure someone has better numbers, but chemical activity is
    temperature dependent. IIRC it doesn't matter much what the
    reaction is.
     
  18. bud--

    bud-- Guest

    In my normal driving I don't make many fast stops. Prius has smaller
    than normal brakes because of regenerative braking. And the city mpg
    (stop and go)is better than highway. Regeneration must be quite effective.
    I read Prius wants to keep battery charge between 40 and 60% of capacity
    because it gives longer battery life (NiMH). I suspect on a long descent
    they would run it up to 100%.
     
  19. krw

    krw Guest

    There is no benefit to a hybrid at highway speeds because the engine
    has to run anyway. .,..and you're lugging the weight of the
    batteries along for no benefit.
    I would seem to be a *LONG* descent charge .4C or the batteries are
    too small to be of much use.
     
  20. bud--

    bud-- Guest

    ..
    You can use a smaller engine, with battery/electric motor added for when
    you need more power - acceleration, ascent. (For a very long fast ascent
    where battery assistance is required you can run out of battery.) The
    smaller engine operates at a more efficient point. The benefit - around
    44 mpg highway for a Prius.

    And with a conventional car you are lugging the weight of the higher
    horsepower of the engine that is not being used most of the time.

    In a Prius, at higher speeds the engine - through the transmission -
    does not turn the wheels fast enough. One of the 2 electric motors is
    used as a generator feeding the 2nd motor. That operates through a
    planetary drive to increase the wheel speed. [See Hybrid Synergy Drive
    in Wikipedia.]

    The engine, by the way, is a variation that uses an Atkinson cycle
    (which I had never heard of).
    ..
    ..
    Design of anything is a series of trade-offs.
     
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