Can an electric vehicle charge itself?

To bring in more detail, I was just sitting here at my desk thinking how come electric cars cant charge themselves. Well, I dove more into this question and found that of course about perpetual motion and the second law of thermodynamics. When mechanical energy is converted into electricity, what is the output? (let's say an electric motor being run by batteries) the mechanical energy output being produced from the electric motor can never be higher than the input from the electric motor thus the batteries would never be charged just because of physics. Well, that's understandable I thought but what about the other 2 factors of what's happening, i.e. let's say for instance that electric motor is on a vehicle, that electric motor turns ONLY the front wheels to get the vehicle moving, what about the back 2 wheels which are creating free energy motion, can't you just install an alternator to those wheels which would recharge the batteries, is this possible? Also, what about the wind force hitting around the vehicle, couldn't that be used in some way too? I.E. multiple windmills installed into the grill of the vehicle thus creating wind velocity transformed into electricity? And then third, just to add some extra charging power to the batteries, have an alternator (not too big) to the electric motor? With all these 3 factors combined, wouldn't there be a way to charge these batteries? Hell, if that's not enough, the heat dissipation from the electric motor to be converted into charging amps for the batteries? Or even micro solar panels on the hood hidden underneath the paint to also add some charging amps? So that makes 5, yes 5 separate ideas to charge those batteries, even if on small scale. It just seems to me that with all these combined, that somehow you could create a vehicle that charged itself? Why hasn't it been done? OPEN TO ALL OPINIONS, NO CUSSING PLEASE, THANK YOU.

10 Answers

  • 8 years ago
    Best Answer

    In my college days I had a physics prof who used to run up and down the aisles with a flashlight and admonish us to find all the forces. There are many as you mentioned. The car sits on the Earth and is pulled by gravity. It has sunlight beating down on it. Once we get it moving inertia wants to keep it moving. All these forces are potentially adding energy to the vehicle.

    Against this there are forces that take away energy from the vehicle. We have wind, rolling and mechanical resistance, gravity again, and also a tendency for energy not to stay in one place but to spread out as heat travels from what is warmer to what is cooler. When we look at all these forces we add up all the positives and all the negatives, they should be equal because energy is not created or destroyed. (on a greater than atomic level) Just because it may seem like there is a "lot" of energy or a "lot" being wasted does not mean that the equation is not in equilibrium.

    When we add the right kind of energy to the system balance is achieved by the addition of motion. When we take away energy from the system balance is achieved by decreasing the momentum.

    What we can do is slide the allocations a bit and make more of the energy useful. This is how we increase efficiency. What you want to do is make it so efficient that it produces more energy than is used. The problem is that the resistance factors are going to be there. Air is not going to jump our from in front of our vehicle. Tires roll but there is resistance on the road. Motor parts will wear against one another.

    A car has inertia. This is what carries it forward even if you cut the engines. We can tap into that energy as we do with regenerative braking, imagined fans, generators on non-drive wheels, but no matter what way we do this we will necessarily be subtracting from the vehicle's inertia. This by definition must slow the vehicle. We can't efficiently make the vehicle go forward by slowing it down.

    The only way we can get a vehicle to "charge itself" is to provide an energy source external to the system that already providing power. An example is robot vacuum cleaner. These nifty devices will roam your halls vacuuming the floor and then find its charging station and essentially plug itself in. With electric cars we could have systems where the vehicle can wirelessly power and charge itself from wires buried in our garage floors or even in the roadway. In both cases the power to charge is in addition to the power to operate the vehicle.

  • 8 years ago

    Stuff like running a motor on the front wheels and a generator on the back wheels is perpetual-motion nonsense.

    However, adding solar panels on the roof or regenerative braking so that the batteries charge when you slow down is reasonable. It's just not always economic (regen braking is and is used in e.g. the Prius, but solar panels are only enough to run a fan to keep the inside cool, unless you make the entire car a panel like the solar racers in Australia).

    Yes, the wind can be used. It's called a land-yacht. There are issues around hoisting sail on the highway. I do recall some experimental car that was designed to get energy from the wind from having some kind of wing shape, but I don't see any in production so it can't have worked that well, or had other limitations like no passengers)

    You can't efficiently get low-level heat from motors or brakes back into electricity. Thermoelectric effect devices exist but are inefficient. I did wonder if you could use the heat from brakes to heat the passenger compartment somehow in winter, but again the economics may just not work out (extra weight from hoses or long ducts, plus construction costs)

  • Mr.357
    Lv 7
    8 years ago

    It is good that you know of the existence of the second law of thermodynamics. Obviously you do not understand it. Alternators on the rear wheels will just cause extra load on the motor driving the vehicle causing it to use more energy. You could use alternators to moderate the speed going down hill and recover SOME of the energy required to move the vehicle to the top of the hill. Same with windmills. It will put extra load on the motor. Solar panels or capturing the heat from the motors and brakes would help increase the distance that the vehicle could travel.

  • Jeremy
    Lv 5
    8 years ago

    In short it cant.

    The back wheel generators would still derive energy from the electric motor. Once again the laws of thermodynamics wins. As it always will. Im glad you mentioned that law. Now I know youre not a dipshit. Thank god. Some people say things like a perpetual motion machine and think theyre on to something. Lol

    The wind velocity turning generators is the same thing. The vehicles motion (the relative air) will get energy from the motor.

    The heat dissipation could be used. Its 'free' energy, more precisly its wasted energy. But that would be hard to get energy from. Same with solar panels. Its free enrgy that doesnt come from the electric motor so you could make some gain from it.

    Remember you cant, CANT make a vehicle that powers itself. You have to get outside energy from somewhere, but what youre trying to is recoup lost energy. Which is exactly what you need to do. Another thing used on hybrids are generators attached to brakes. So the energy lost during braking (heat, sometimes noise if your brakes suck) can be recovered. Most of the energy of your vehicle (energy=.5(mass)(velocity²)) is lost as heat during braking. Its a huge waste. Plug some sample numbers into that formula...thats ALL lost as braking heat, and some can be recouped.

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  • 8 years ago

    Windmills will create extra drag, and I think a second alt will as well. I think the rear alt is a good idea, but it should only recharge by a proportion and not completely since the force required to move the vehicle relates to turning all four wheels plus the vehicle weight (inertia). So you can't get back as much as is put in since some of the energy will be lost through resistance etc between battery and wheels while being spent, and more from alt to battery in being charged. But it could reduce the charging required.

    I'm not an engineer btw so I make these statements based on complete ignorance, just guessing.

  • Anonymous
    6 years ago

    Mechanical engineering, a gearboxes can generate several hundred (1600) cycles per wheel rotation. using these multiples off an axle combined with several generators can produce enough energy to run an electric motor. 20 years before the Ford model T engineers stated the drag from the mechanical components would not a leave a sufficient amount of energy to propel the vehicle forward. The Ford Model T did just fine.

  • 8 years ago

    It can, but never fully recharge in practical terms due to all kinds of limitations of various parameters.

    Any sort of regenerative devices will no doubt have a weight associated with them, and must be transported with the vehicle, and that takes additional energy. All systems save for PV solar, will hae some sort of rotating machinery associated with them and there will be friction losses. All systems including PV solar, will have resistance / heat loses. It increases dramatically in PV as the ambient heat increases. The laws of Conservation of Energy dictate that Energy cannot be created or destroyed in a closed system. You can't get it from no where, and it all gets accounted for in the equation. There is really no system that is 100% efficient, that would be a perpetual motion machine.

    On the other hand, back to the "it can" part of the answer, you can recapture some of the energy expended by the vehicle by way of dynamic braking and recharging on down grades slopes.

  • Steven
    Lv 6
    8 years ago

    In theory they can when they reach the top of a hill and coast down the other side that motor can then generate electricity to be put back in the battery but because everything has a lose (is not 100% efficient) it will eventually run out of power. It can be supplemented with solar power but since the sun is not up all day in most places that will just delay it more.

  • Rish
    Lv 4
    8 years ago

    EVs do charge themselves up when coming down a hill or under sunshine but the charging is a very small percent of the total charge needed by the batteries. This technology is under use but it contributes very less to the power saving as of now.

    And the option that you have listed will increase both the price and weight along with the bulk of the car. All solutions need to be commercially feasible so that a publicly affordable car is made.

  • 8 years ago

    i am also finding the same answer friend.

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