Help me explain...

[tomislavp4]

Hi guys, I have a trouble explaining somehting to someone and I wonder how would you explain the thing, why won´t it work?

1. Let´s say you connect some kind of a multiplication gear to the driveshaft of a electromotor. Then you connect a generator on the other side, connect a small battery to the electromotor and then connect the generator to the electromotor.
You use the battery to start the electromotor, then the multiplication gear turns the generator with speed greater than the speed of the motor, let´s say 4 times faster feeding the engine with the neccesary power+producing extra power for other purposes. So it´s hard for me to explain why this won´t work

2. Or you put a propeller on the car, it is connected to a generator. You drive at highway, the air spins the propeller and it creates electricity. Now this will work, but what amount of power could you expect it to produce?

Thanks,

[Ciro Pabón]

Well, you get 4 times the speed, but you also get 4 times less torque. If you do the math, the power is the same, minus the losses at the gear train.

About the car and propeller, Lord Kelvin stated it like this:

"It is impossible to convert heat completely into work."

Which loosely means that you cannot expect to have a machine with 100% efficiency (in the macroscopic world, to be precise). Some of the heat you get from the source of energy must go back to a sink with a lower temperature.

In real life efficiencies for the kind of regenerative machine you describe are around 30%. If you combine two cycles (for example, if you take the heat from the air that pass around the propeller ) you can expect 60% efficiency, but you have to be good at it.

[Tom]

The propellar theory is a good idea but the car would create more drag and the energy needed to overcome this would probably nullify the energy gained from the propeller.

[Giblet]

For every turn of the prop shaft there is resistance on the motor/generator, resulting in parasitic losses from the get go.

So the engine in the car has to push the added weight of the generator, resulting is losses.

The generator attached to the propeller resists every turn of the prop shaft, resulting in losses.

The air resistance of the propeller results in losses.

It would simply make more sense to split the power from the motor to drive the generator directly, which would result in more effectient losses then the propeller, but losses nonetheless.

Since the power you would get would be from air resistance, it's not free power.

Now if the the car had a turbochager on the exhaust manifold, but instead of the impeller driving a compressor, it could be used to spin a generator, since the exhaust is free power resulting from existing losses in the motor.