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Electric cars

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

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  1. Roy

    Roy Guest

    From: bud
    krw says...
    John Gilmer wrote:

    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.
    True.   But the energy gained is, IMO, somewhat exagerated. In true
    "stop & go" driving when you want to "stop" you want to STOP and you
    don't want to screw around with "slowing down" with regenerative braking
    first. Regeneration would work best on a long downhill stretch (without
    STOPPING) after a long uphill stretch.
    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
    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.

    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).

    A hybrid has many of the same advantages although unless the power
    management is somewhat predictive the cells might already be at 100%
    charge when the regenerative braking is call upon.
    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%.
    I would seem to be a *LONG* descent charge .4C or the batteries are too
    small to be of much use.

    Design of anything is a series of trade-offs.
    Roy responds: I agree., specially designing something as systemic as a
    car., Therfor Quality Control is essential I believe this is where
    product support came to play for product longevity.

    Amazing what a beer or two does to refresh & calm me };-)

    " Have a Great Weekend "

    Roy Q.T. ~ US/NCU ~ E.E. Technician
    [have tools, will travel]
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