Electric vehicles have regenerative braking, where the brake hardware can generate some electricity to slightly recharge the batteries. So why can’t they come up with some system where the wheels moving can also generate electricity? Sort of like how the alternator in a gas car works, where it’s driven off of the engine to recharge the 12V battery. Maybe build something into the wheel hub to generate electricity when the wheels are moving?
Edit: I don’t mean there should be an infinite amount of electricity created, but rather generate enough to recoup some losses, like how regenerative braking also works
In: Engineering
That would introduce additional load on the electric motor. In a perfect universe, this alternator could exactly compensate for the additional load but, real world and all, some energy will be lost as friction, heat, physical wear on the parts, etc. and you’ll still see a net loss of power.
The other responses are true. Here is another way of looking at it. Ice’s (internal combustion engines) have to produce power to make the alternator move and generate current. That has some load attached to it depending on the generator. If you put that on a electric car you’re expending electricity and stored energy to produce power (cars motors) to then power another alternator. This would have an efficiency curve where power in is less than power out. So you’re adding another load to the car while accelerating for no reason other than to lose energy due to heat. Which is where braking comes in. There you’re not wanting to accelerate but decelerate. Now you’re taking energy from your cars motion to then transform and store it as electrical power in the battery.
Because that’s exactly what brakes do: taking some kinetic energy from the car moving and converting into some other form of energy.
You can’t just create energy out of thin air; it has to come from somewhere.
To put it as simply as I can, you can’t get more energy out of something than you put into it. Laws of thermodynamics and all that. What you’re suggesting would be perpetual motion which is impossible.
I mean, I’m sure you could put some generator on the wheels but it wouldn’t produce any more power than it’s using to turn the wheels.
Because if it used the wheels spinning for electricity it would slow them down, needing more power to drive faster, and friction would just lower efficiency and speed
If you have ever played around with a hand cranked generator, you might have noticed that when an electrical load is put on the generator (such as connecting it to a rechargeable battery) it makes the generator much harder to turn. In a car, this means that using the wheels to generate energy makes the wheels resist being turned, so they act like breaks. That is how regenerative breaking works, and there is no way around this limitation. You could use generators to get energy from the wheels, but in order to keep the car moving the motor needs to work harder to turn the generators which consumes more additional power then the generators could ever produce.
The OP might be interested in this Prof Lewin lecture where he discusses storing energy in flywheels (from 13:45):
Engineering student here
If you put electricity through wires within magnetic field in a fancy way then wires move.
If you move wires within magnetic field in a fancy way then electricity happens.
If you try to do the latter, you’ll feel some sort of resistance as you’re trying to move the wire, as if a force is pushing against it.
Will make car slower…
> So why can’t they come up with some system where the wheels moving can also generate electricity?
Because generating electricity in this way slows the wheels down, and it doesn’t make enough energy to equal what was spent making it. Regenerative braking only works because “slowing down” is what we want in that case.
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