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Posted by Androcles on June 6, 2009, 1:28 pm

> tgdenn...@earthlink.net wrote:
> >>> I think maybe you are not reading carefully and just overreacting. I
> >>> said that electric motors can be reversed, which means that they have
> >>> as much 'stopping potential' as they have starting potential.
> >> But they do not.
> > Now you are being silly. Do you understand what reversing the motor
> > means?
> "as much stopping potential as starting potential" is incorrect. It is
> not proportionate. The stopping potential depends upon the electrical
> load of the system. More 'need for juice' == greater stopping power.
> Using the electric motor as a brake in an automobile requires a load on
> the electrical system. Granted, such is usually the case, for example
> when the battery is not fully charged and an appliance or the lights are
> on. Regardless, super capacitors can add to the necessary load.
> But it's not proportionate. Not really.

Ok, now I can see that you actually don't get what I am saying. By
reverse, I don't mean "reverse the function so the motor becomes a
generator". I mean "reverse the direction that the motor is trying to
turn", which will actually *use* battery juice that is already stored.

Remember, the original question was whether you can bring the car to a
complete stop using only electricity and no mechanical brakes. The
answer is yes.

You are correct that it is not a simple 1:1 relationship in a
practical sense to stop the car with the generator effect. The most
obvious reason is that you usually would like to stop faster than you
have accelerated to the current speed, and you may be going downhill
as well. This means that even if you 'short' the motor<>generator as
someone suggested, the kinetic energy of the car will be have to be
dissipated as heat at a rate that will prevent damage to the motor.

I am suggesting that there will be a combination of effects used to
provide the system load, and that over time, it will develop into a
mostly electric system which gives ABS, and mechanical brakes will be
a back-up component and for parking. Right now, it isn't even legal to
have a car without mechanical brakes, no matter how reliable electric
braking could be made, so the argument is purely academic.

-tg

'Don't worry about people stealing your ideas. If your ideas are any good,
you'll have to ram them down people's throats.' - Howard Aiken


> Aside: the lights and accessories of the conventional car draw extra
> horsepower than if they were off. It's related to the load on the
> alternator/generator. So driving with everything on causes a minor loss
> in mileage. Oh, and your alternator does not recharge the conventional
> car system when you take your foot off the gas at speed because it's
> engineered (using a diode) to direct the juice one-way. Removing that
> diode will raise hell.
> A funny and pathetic aside - At one time Volkswagen used the generator
> warning light bulb (a tiny thing in the speedometer) to first energize
> the alternator's field so that it would generate electricity. If that
> stupid bulb burned out, then after you stopped the engine and started it
> again, you just drew from the battery because the alternator was not
> energized, was not charging. Lesson: if it did not come on don't just
> think "aw it's just an affirmation bulb" and drive away - your battery
> will discharge eventually and turn you into a pedestrian. (problem
> solved with tiny resistor in circuit.)




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