electric car idea

[doubleM]

this isnt really under electronics but it would definitely involve it. im not sure if this would work but i havent seen any car already that use it. im not trying to come up with a perpetual motion machine. i was hoping some more experienced people can shed light on it.
i had an idea about an electric car. im picturing how a normal electric car works: you have batteries, electronics to regulate voltage and current, and a electric motor driving 2 wheels. why not add a generator to recharge the batteries. the generator can be driven by the 2 wheels that are not driven. or the generator can be used to partially power the electric motor.
like said this would not fully power anything, but it would help alot. i know this would affect weight, hp, etc. you would be harnessing the rolling energy the car already has to generate electricity. has anyone tried this? any input?

 

[MikeMl]

Imagine a car moving at a constant speed along a level road. It takes a certain amount of HP (X) just to overcome aerodynamic drag and friction. Now couple your generator to the front wheels. It will take X+Y HP to keep the car moving, where Y is due to the braking effect of turning the generator. Because of intrinsic losses in the generator, the amount of electric power you can get back out of the generator is less than Y, so what you have done is like driving the car with the brakes partially applied, it just takes more HP to keep it moving.

This is an example of trying to make a perpetual motion machine...

 

[doubleM]

would a small generator cause that much rolling resistance? as i said im not trying to make a perpetual motion machine, as i know that cannot exist. i just believe there can be a gain to make it last longer.

 

[dknguyen]

It doesn't matter how little resistance the generator has because whatever generator resistance is there requires the engine to produce extra power to drive the generator. You aren't recovering energy that would otherwise be lost- what you are actually doing is spending extra energy needlessly and recovering a portion of THAT extra energy. And the amount of extra power required by the engine to drive the generator is always going to be more than what the generator is producing (due to less than 100% efficiency).

Now...during regenerative braking, that is different since you are trying to recover kinetic energy stored in the inertia of the car that would otherwise be lost as heat when braking (you aren't actually using the engine to drive the load presented by the generator). This would require engaging the generator only when the brakes are applied (having it run all the time woudl present the same problem as above and actually reduce mileage).

 

[misterT]

would a small generator cause that much rolling resistance? as i said im not trying to make a perpetual motion machine, as i know that cannot exist. i just believe there can be a gain to make it last longer.

There is a generator in every electric car. This is because the motor and the generator is the same device. When the car accelerates and does work against all the friction and drag, electrical energy is converted to mechanical energy by the motor. When the car decelerates, the mechanical energy is converted back to electrical energy (by the same motor) and stored in the batteries.

If you could generate electricity from the heat that the motor and other parts produce.. that would help a little (in theory).

 

[audioguru]

A guy tried a computer fan as a generator to charge batteries on his bicycle but the charging current was too low.
Then he tried a huge fan that worked. But the extra amount of energy that he needed was like dragging an open umbrella or parachute around behind him.

 

[Sceadwian]

As DK said, this is called regenerative breaking, it's already fully utilized on most electric and hybrid vehicles, though mechanical breaks are ultimately responsible for stopping the vehicle.