Probably a dumb question....but

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Old 18 Jan 2008, 06:55 pm   #1 (permalink)
mack
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Default Probably a dumb question....but

While driving this morning and watching a Prius pass me, I had an idle
thought, but I'm not enough of a physicist to know whether it merits further
study.

If one had an all electric vehicle, with a passel of batteries in the trunk
and under the hood, and attached some sort of generator or dynamo to the
running gear, why couldn't you generate electricity to recharge the
batteries? I know that in theory it's impossible to create a perpetual
motion machine, and that there has to be some loss of power when charging a
battery, but (to the physics majors and Popular Science readers on the ng)
what is the reason that this sort of thing wouldn't work?


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Old 18 Jan 2008, 07:06 pm   #2 (permalink)
Jeff Strickland
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Default Re: Probably a dumb question....but


"mack" <mackerel@dslextreme.com> wrote in message
news:13p2ij9jt680hb2@corp.supernews.com...
> While driving this morning and watching a Prius pass me, I had an idle
> thought, but I'm not enough of a physicist to know whether it merits
> further study.
>
> If one had an all electric vehicle, with a passel of batteries in the
> trunk and under the hood, and attached some sort of generator or dynamo to
> the running gear, why couldn't you generate electricity to recharge the
> batteries?


You can, and they do.




I know that in theory it's impossible to create a perpetual
> motion machine, and that there has to be some loss of power when charging
> a battery, but (to the physics majors and Popular Science readers on the
> ng) what is the reason that this sort of thing wouldn't work?
>

It takes more energy to propel the car than the car can generate, but when
the car is coasting, it can create more energy that it takes to make it go.
They have devices on them that "clutch" in the forward direction of travel,
but when the car is coasting the clutch lockes up and drives a generator.
So, when an electric car is going down a hill, it can create energy that is
stored in the battery for future use.



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Old 18 Jan 2008, 07:27 pm   #3 (permalink)
Mr4701
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Default Re: Probably a dumb question....but


"mack" <mackerel@dslextreme.com> wrote in message
news:13p2ij9jt680hb2@corp.supernews.com...
> While driving this morning and watching a Prius pass me, I had an idle
> thought, but I'm not enough of a physicist to know whether it merits
> further study.
>
> If one had an all electric vehicle, with a passel of batteries in the
> trunk and under the hood, and attached some sort of generator or dynamo to
> the running gear, why couldn't you generate electricity to recharge the
> batteries? I know that in theory it's impossible to create a
> perpetual motion machine, and that there has to be some loss of power when
> charging a battery, but (to the physics majors and Popular Science readers
> on the ng) what is the reason that this sort of thing wouldn't work?


You mean like the tires generating electricity as they go? Kind of like the
way a windmill makes electricity?



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Old 18 Jan 2008, 07:29 pm   #4 (permalink)
Mr4701
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Default Re: Probably a dumb question....but


"Jeff Strickland" <crwlr@verizon.net> wrote in message
news:z2ckj.345$8A4.180@trnddc02...
> It takes more energy to propel the car than the car can generate, but when
> the car is coasting, it can create more energy that it takes to make it
> go. They have devices on them that "clutch" in the forward direction of
> travel, but when the car is coasting the clutch lockes up and drives a
> generator. So, when an electric car is going down a hill, it can create
> energy that is stored in the battery for future use.


Commercial Jetliners have fans that pop out on the plane when the plane
loses electricity...it creates just enough electricity to run the pannels on
the plane... i wonder even though it would be little electricity... how
much could be created with fans in the vent in front... especially on the
highway.


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Old 18 Jan 2008, 07:29 pm   #5 (permalink)
Jeff
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Default Re: Probably a dumb question....but

Jeff Strickland wrote:
>
> "mack" <mackerel@dslextreme.com> wrote in message
> news:13p2ij9jt680hb2@corp.supernews.com...
>> While driving this morning and watching a Prius pass me, I had an idle
>> thought, but I'm not enough of a physicist to know whether it merits
>> further study.
>>
>> If one had an all electric vehicle, with a passel of batteries in the
>> trunk and under the hood, and attached some sort of generator or
>> dynamo to the running gear, why couldn't you generate electricity to
>> recharge the batteries?

>
> You can, and they do.
>
>
>
>
> I know that in theory it's impossible to create a perpetual
>> motion machine, and that there has to be some loss of power when
>> charging a battery, but (to the physics majors and Popular Science
>> readers on the ng) what is the reason that this sort of thing wouldn't
>> work?
>>

> It takes more energy to propel the car than the car can generate, but
> when the car is coasting, it can create more energy that it takes to
> make it go. They have devices on them that "clutch" in the forward
> direction of travel, but when the car is coasting the clutch lockes up
> and drives a generator. So, when an electric car is going down a hill,
> it can create energy that is stored in the battery for future use.


Energy can neither be created nor destroyed. Rather energy is converted
from one form to another. (Energy can be converted to matter and vice
versa - read up on Einstein theory or relativity.)

To get the car to the to[p of the hill, potential chemical energy
(either in the battery or the liquid fuel) is converted to kenetic
energy (the energy of motion). In addition, as the cars go higher, some
of the energy is converted to potential energy - the ability of the car
to do work because of the force of gravity.

So the potential graviational energy that is converted to kinetic energy
and be converted to eletrical energy and stored in the batteries is not
free energy. The energy came from gasoline or another fuel.

Jeff
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Old 18 Jan 2008, 07:33 pm   #6 (permalink)
Jeff
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Default Re: Probably a dumb question....but

Mr4701 wrote:
> "Jeff Strickland" <crwlr@verizon.net> wrote in message
> news:z2ckj.345$8A4.180@trnddc02...
>> It takes more energy to propel the car than the car can generate, but when
>> the car is coasting, it can create more energy that it takes to make it
>> go. They have devices on them that "clutch" in the forward direction of
>> travel, but when the car is coasting the clutch lockes up and drives a
>> generator. So, when an electric car is going down a hill, it can create
>> energy that is stored in the battery for future use.

>
> Commercial Jetliners have fans that pop out on the plane when the plane
> loses electricity...it creates just enough electricity to run the pannels on
> the plane... i wonder even though it would be little electricity... how
> much could be created with fans in the vent in front... especially on the
> highway.


The problem is that the energy needed to turn the fan comes from the
motion of the vehicle. Putting the fan on there would increase the
resistance of the car going through the air, which would increase the
amount of energy needed to propel the car.

Instead, it makes more sense to drive a generator or alternator directly
off the engine.

I bet you could get a few kilowatts of such a generator.

Jeff
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Old 18 Jan 2008, 08:46 pm   #7 (permalink)
tak
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Default Re: Probably a dumb question....but


"mack" <mackerel@dslextreme.com> wrote in message
news:13p2ij9jt680hb2@corp.supernews.com...
> While driving this morning and watching a Prius pass me, I had an idle
> thought, but I'm not enough of a physicist to know whether it merits
> further study.
>
> If one had an all electric vehicle, with a passel of batteries in the
> trunk and under the hood, and attached some sort of generator or dynamo to
> the running gear, why couldn't you generate electricity to recharge the
> batteries? I know that in theory it's impossible to create a
> perpetual motion machine, and that there has to be some loss of power when
> charging a battery, but (to the physics majors and Popular Science readers
> on the ng) what is the reason that this sort of thing wouldn't work?

Google locomotives--regenerative braking--for an explanation of the concept,
uses, and limitations of your idea.

Tom


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Old 18 Jan 2008, 09:27 pm   #8 (permalink)
Tegger
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Default Re: Probably a dumb question....but

"mack" <mackerel@dslextreme.com> wrote in
news:13p2ij9jt680hb2@corp.supernews.com:

> While driving this morning and watching a Prius pass me, I had an idle
> thought, but I'm not enough of a physicist to know whether it merits
> further study.
>
> If one had an all electric vehicle, with a passel of batteries in the
> trunk and under the hood, and attached some sort of generator or
> dynamo to the running gear, why couldn't you generate electricity to
> recharge the batteries? I know that in theory it's impossible to
> create a perpetual motion machine, and that there has to be some loss
> of power when charging a battery, but (to the physics majors and
> Popular Science readers on the ng) what is the reason that this sort
> of thing wouldn't work?
>
>




Because... entropy always increases.

Using the electric motor's own motive force to recharge its own battery is
akin to eating yourself in order to stay alive.

The effort needed to move the mass /and/ recharge the power source
(battery) would deplete the power source faster than if you used the power
only to move the mass instead of trying to move the mass and recharge its
motive power source at the same time.

--
Tegger

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Old 18 Jan 2008, 09:52 pm   #9 (permalink)
johngdole@hotmail.com
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Default Re: Probably a dumb question....but

I think you pointed it out clearly: because no battery, motor or
generator is 100% efficient you will always consume more power than
the closed system can produce.



On Jan 18, 4:55 pm, "mack" <macke...@dslextreme.com> wrote:
> While driving this morning and watching a Prius pass me, I had an idle
> thought, but I'm not enough of a physicist to know whether it merits further
> study.
>
> If one had an all electric vehicle, with a passel of batteries in the trunk
> and under the hood, and attached some sort of generator or dynamo to the
> running gear, why couldn't you generate electricity to recharge the
> batteries? I know that in theory it's impossible to create a perpetual
> motion machine, and that there has to be some loss of power when charging a
> battery, but (to the physics majors and Popular Science readers on the ng)
> what is the reason that this sort of thing wouldn't work?


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Old 18 Jan 2008, 11:06 pm   #10 (permalink)
Ray O
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Default Re: Probably a dumb question....but


"mack" <mackerel@dslextreme.com> wrote in message
news:13p2ij9jt680hb2@corp.supernews.com...
> While driving this morning and watching a Prius pass me, I had an idle
> thought, but I'm not enough of a physicist to know whether it merits
> further study.
>
> If one had an all electric vehicle, with a passel of batteries in the
> trunk and under the hood, and attached some sort of generator or dynamo to
> the running gear, why couldn't you generate electricity to recharge the
> batteries? I know that in theory it's impossible to create a
> perpetual motion machine, and that there has to be some loss of power when
> charging a battery, but (to the physics majors and Popular Science readers
> on the ng) what is the reason that this sort of thing wouldn't work?


The energy required to run a generator would drain the batteries more
quickly than the power they add due to frictional losses.
--

Ray O
(correct punctuation to reply)


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