Can someone please explane to me

[Ron C]

Why we can't make an electric car that recharges itself?

If a gas car can use a alternator to recharge it's battery and run the car while you are driving, then why can't an electric car use a alternator to recharge it's own batteries?

[pewd]

and what, exactly, would you use as the source of the energy to drive the alternator? the battery? drain down the battery to charge it ? you'd get nowhere. actually, you'd run down the battery , nothing is 100% efficient.

you can't create energy out of nothing.

a gas car uses the energy in gasoline to run the alternator.

[ZC1]

Just design it for us, we'll test it out, then we'll proclaim it a "Perpetual Energy Device (brother to the Perpetual Motion Machine), and you'll be instantly and fabuously well known and rich.

Circular thinking will get you everywhere.

ZC1

[ewhanley]

In simple terms: "There is no such thing as a free lunch."
If this were possible, we would have the first perpetual motion machine (a physical impossibility). The alternator on a conventional ICE car is driven by a belt, which is driven by the engine. Some of the mechanical energy created by burning fuel in the engine is used to turn the alternator, thus that energy is not free but is factored into the total fuel consumption of the vehicle. If an alternator was installed on an electric car, the electric motor would have to spin it. So, in a perfect conversion, the energy drawn from the battery to spin the alternator would be replaced by the energy generated by the alternator resulting in a net gain of zero. Compounding the problem is the fact that energy conversion can never achieve 100%, so some of the battery's energy would be wasted in the process, resulting in a negative net charge. A physical model for this would be a tank filled with water (i.e the battery). Out of one side of this tank you have a pipe where water drains out and spins a waterwheel and then drains off into the environment (i.e. the electric motor driven wheels of the car). An alternator would be the equivalent of another pipe on the other side of the tank with water pouring out of it. You could stand there with a bucket (i.e. alternator) catching this water as it spills out and returning it to the tank. Not only would some water spill on the ground while you emptied the bucket back into the tank (conversion inefficiency), but you would not be adding any water to the tank that was not already in it.

[ZC1]

you can't create energy out of nothing.

Energy IS created out of nothing, it's just WE can't do it.

ZC1

[ZC1]

Ron C,
Here's a good graphic example of your question.
Think of the water in the picture as the generated electricity you describe.

Do you see anything interesting here?

ZC1

[minkforce1]

i think what he's driving at (unless it really is asking why we dont have perpetual motion machines) is why we dont use a system like the prius does with regenerative breaking, just with an all electric car, that obviously wouldnt run the motor to recharge the battery thats...running the motor.

unless they already have that.

[darelldd]

Originally Posted by minkforce1

i think what he's driving at (unless it really is asking why we dont have perpetual motion machines) is why we dont use a system like the prius does with regenerative breaking, just with an all electric car, that obviously wouldnt run the motor to recharge the battery thats...running the motor.

unless they already have that.

Uh, yeah. The Rav's definitely already have that. FAR superior to the Prius system. I hope you're right that regen is what is being asked about. Generous of you to consider that!

Unfortuantely, he is talking about "charging while driving." I'm afraid we really are talking about perpetual motion.

[Bob64]

Originally Posted by Ron C

Why we can't make an electric car that recharges itself?

If a gas car can use a alternator to recharge it's battery and run the car while you are driving, then why can't an electric car use a alternator to recharge it's own batteries?

Because the alternator is powered by the engine. And the alternator doesn't power the car's movement, it only powers the electronics.

[bwilson4web]

Originally Posted by Ron C

Why we can't make an electric car that recharges itself?

The second law of thermal dynamics: entropy always increases.

Originally Posted by Ron C

If a gas car can use a alternator to recharge it's battery and run the car while you are driving,

The engine converts about 1/3d of the gas energy into power of which most goes to the wheels to keep the car rolling. The battery has a net energy change of zero, it adds or subtracts as needed to keep the engine in the most efficient power range.

Originally Posted by Ron C

then why can't an electric car use a alternator to recharge it's own batteries?

The electric car battery has to provide power to the wheels to keep it running. To simplify the math, treat this as the 100% efficient path.

If has to also turn an alternator, only about 92-95% of the alternator turning power comes back out as electrical power. This electrical power then has to either go to the wheels (if you are lucky) or into the battery with about 90-92% efficiency. So this worst case means:

.95*.92 ~= 87% efficiency with about 13% being lost as heat
95% if the alternator power goes to the wheels with a 5% loss
100% if the alternator is never involved

Your choice.

Bob Wilson