Why can an electric car, not have a generator instead of a motor on one wheel, so that as that wheel turns it generates energy for the battery? I totally understand that it isn’t possible, but I don’t know why. I also understand that regenerative energy is taken from breaking.
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That’s what regenerative braking is, using exceeds energy from the vehicle’s motion to generate energy when that motion isn’t desired
It takes *work* to crank a generator when it’s putting out electricity. Generators don’t create energy out of nowhere, as energy cannot be created or destroyed. They take mechanical energy away from a moving object and transform that energy into electrical energy. You’ll never get more energy from the generator than the car loses to the generator.
>Why can an electric car, not have a generator instead of a motor on one wheel, so that as that wheel turns it generates energy for the battery
That’s basically what happens during regenerative braking—the generator takes kinetic energy away from the car, slowing it down, and converts it into electrical energy.
The energy lost when you attach the generator to the wheel is more than you get back from creating the electricity.
Because a generator is literally the opposite of a motor. So what you would be doing wouldn’t be LIKE regenerative breaking, it IS regenerative breaking.
You’d literally be breaking while expending energy trying to go forward, just emitting waste heat it the process (which is also the amount of electricity you would lose in the process)
You’d have a $40k space heater.
The generator increases the load, so the motors have to work harder than before. As another said this is regenerative braking. You don’t want to do that while accelerating or maintaining speed, because it would increase the account of effort needed. The motors would have to move the car _and_ turn the generator, in effect, so the generator could never make up for the energy the motors have to use.
To give you an idea why it won’t work, try holding your hands together and try lifting your whole body up in the air by pulling up on one hand with the other. You should find one hand pulling up and the other exerting the same amount of force downwards.
assume the car is set up so the front wheels are connected to the motor pulling the car forward, and the back wheels are connected to the generator, Then to get all of the energy back with the generator, the back wheels would need to pull the car backwards with the same amount of force that the front wheels will be pulling the car forward. The result will be that the car goes nowhere.
And if electricity is sent to the motor without it moving, all of the electrical energy going to the motor would be converted to waste heat.
Conservation of energy:
1. Normally the motor needs to put out enough energy to make all 4 wheels turn
2. If you put a generator on one wheel, that wheel needs enough energy to turn all 4 wheels and move the car + turn the generator
So what you have is a car with a motor that puts out enough energy to turn 4 wheels plus the generator. And the energy from the generator goes back directly to the battery.
No motor nor generator are 100% efficient, so you actually have a motor that uses enough energy to turn all 4 wheels and move the car + turn the generator + whatever energy loss you have along the way. This is more energy than just moving the car.
It takes energy to spin a generator. The term generator is a bit of a misnomer. Generators actually convert chemical energy into electrical energy. They do generate electricity, but not for free. It costs fuel.
If you were to hook a “generator” to one of the wheels of an electric vehicle you would be converting kinetic energy into electrical energy. Which is the reverse of the process you used to make the wheel spin in the first place.
In a perfect world with perfect efficiency the “generator” would cause as much drag on the wheel as it produced by turning and you wouldn’t get anything for your effort.
However, in the real world there are losses to rolling resistance, friction in the wheel bearings and generator, and electrical resistance. Not to mention the added weight of the generator and wiring.
Actually, there are electric cars where turning the wheels generates electricity: The Rivian trucks can be towed and load the batteries while being towed.
But there will always be more nergy necessary to move the vehicle with the motor than can be gained by moving the vehicle from the outside, generating electric energy. A perpetuum mobile (generate a little more electricity than you get from a generator moved by the same car) is not possible..
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