Question about the electric car and its engine.

[brentyoung]

Hello, I dont know much about mechanics, I fix things that break down on my car as they come and am in no sense an engineer, however I do understand some of the mechanics of how a motor works, so this may seem like a stupid question to those of you who have the answer.

Here it goes:

On a gasoline powered engine you have an alternator that charges the battery, which is used to start the car and provides a tiny amount of energy to all electronics that are ran by the car, the alternator runs off a pully system that engages with the turning of the motor.

Then why cant you, on an electric vehicle, use a wall plug of some sort to charge overnight or while idle and to get you going, but then on the road have an alternator which keeps your battery constantly charging, sort of a self propelled engine that just needs a little kick. Or for that matter it should be fully charged when you turn the vehicle off, therefore allowing you to start the vehicle without the need of charging overnight.

Again I understand that my solution is so simple that there must be some sort of a hang up as to why this cant be done I would just really like the answer.

Thank you.

[curtis73]

the law of conservation of energy. You can't get something for nothing. Let's say it takes 100 amps to keep the car moving at 50 mph. The electric motor is taking 100 amps from the batteries and converting it into other forms of energy. If it were 100% efficient, it could turn it all into motion, but in truth the wiring gets hot converting some of it to heat. The motor gets hot and has friction so more gets lost to heat. EMI interference loses some to light energy. So, of the actual 100 amps the battery is giving up, only about 60 amps worth is actually driving the car. The rest is wasted.

So if you put a 100 amp alternator on it, you're now requiring a few hp to drive the alternator, which takes more power, which requires more alternator, which takes more power.... ad infinitum.

Try it sometime. Put an electric motor on a car battery, attach it to an alternator which charges the battery, and let it go. It'll die, possibly sooner than just running a motor alone without an alternator. If both components were 100% efficient, you could create a perpetual motion machine, but since there is always energy loss to friction, heat, resistance, belt friction, efficiency of the component, and a million other things, its not possible. Every time you convert energy you lose a buttload, so its more efficient to only convert energy as few times as possible. Hence my deep hatred for hybrids

[GreyGoose006]

but the regenerative brakes are pretty cool... you gotta admit.

[curtis73]

Yes, cool, but they still waste a ton of energy to heat.

[GreyGoose006]

not as much as regular brakes tho where all the energy is wasted