Probably a dumb question....but

"mack" wrote in message

> 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)
 >> Stay informed about: Probably a dumb question....but 

"mack" wrote in message

> 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.
 >> Stay informed about: Probably a dumb question....but 

"mack" wrote in message

> 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?
 >> Stay informed about: Probably a dumb question....but 

"Jeff Strickland" wrote in message

> 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.
 >> Stay informed about: Probably a dumb question....but 

Jeff Strickland wrote:
>
> "mack" wrote in message
>
>> 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
 >> Stay informed about: Probably a dumb question....but 

Mr4701 wrote:
> "Jeff Strickland" wrote in message
>
>> 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
 >> Stay informed about: Probably a dumb question....but 

"mack" wrote in message

> 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
 >> Stay informed about: Probably a dumb question....but 

"mack" wrote in


> 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
 >> Stay informed about: Probably a dumb question....but 

In my opinion, the key for an all electric vehicle is the battery plus
what is popular nowadays called *super* capacitors, that discharge
current faster than a regular battery.

Given the chance, I still wouldn't buy an ALL electric car, like the
Tesla. I like the idea of a plugin vehicle with a standby engine for
long distance driving and battery charging. However that engine would
NOT need to be sensitive to maintenance. I mean, when would you change
the oil if the engine is almost never used.

Anyway, what I understand form the OP is, given a car have driven
wheels in the front why not use the rear wheels to generate
electricity. This would mean load for the engine but the car was
designed to carry 5 people and cargo, if there was a sensor that
detects the passengers cargo when only carrying 1 or 2 passengers, a
clutch would engage and engage the generator such that it was just
carrying the max load. Its just using the full potential of the engine
to generate reserve (and not complete perpetual motion) charge. So its
just making use of the wasted energy. But then again, does the revised
EPA estimates consider 1 or 5 passengers?
 >> Stay informed about: Probably a dumb question....but 

On Sat, 19 Jan 2008 01:29:03 GMT, "Mr4701" wrote:

>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.

Those little fans need serious speed to work. Way above highway
speeds.
 >> Stay informed about: Probably a dumb question....but 

On Fri, 18 Jan 2008 16:55:02 -0800, "mack"
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?
>
You have GOT to be kidding!

According to your logic, you wouldn't need a car. Hope on your
bicycle, pedal it up to speed and coast for the rest of the trip. You
don't need batteries, generators, electric motors or fuel.

GEEZE!!!! God gave you a brain, use it!
 >> Stay informed about: Probably a dumb question....but 

"Jeff" wrote in message

>
> 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


All of what you say is true, but in the context of the discussion, it is
irrelevent.

In the context of a car, one must drive to the top of the hill at any cost
of energy, and the ride down the hill can be used to generate more energy
that can be stored to be used later.
 >> Stay informed about: Probably a dumb question....but 

Jeff Strickland wrote:
>
> "Jeff" wrote in message
>
>>
>> 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
>
>
> All of what you say is true, but in the context of the discussion, it is
> irrelevent.


You wrote (to which I was replying): "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."

I was pointing out that you cannot create energy.

> In the context of a car, one must drive to the top of the hill at any
> cost of energy, and the ride down the hill can be used to generate more
> energy that can be stored to be used later.

Right. But when you get to the bottom of the hill, although the total
amount of energy is the same, some of the energy has been permanently
lost as heat from friction and in electrical losses. By lost, I mean
that the energy cannot be used again to do useful work.

Obviously, the energy that is recovered and stored in batteries or is
kinetic energy (the energy of motion) is not lost.

Jeff
 >> Stay informed about: Probably a dumb question....but