Home » Why You Can’t Put A Wheel Generator On Your EV And Drive Forever

Why You Can’t Put A Wheel Generator On Your EV And Drive Forever

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There’s a certain post that floats around the Internet with some regularity, and it caught my eye. It shows us a Chevy Bolt with what appears to be some kind of generating apparatus attached to the rear wheel. The post states that the rotation of the car’s wheel is used to recharge the EV’s battery as it drives along, avoiding charging stops and paying for electricity! Genius, right?

And yet, we know that’s too good to be true. If slapping an alternator on the rear wheels was enough to make electric cars run forever, everyone would be doing it. We’d never burn a drop of petrol again.

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You might be wondering, though, precisely why this doesn’t work. Or, you might have a rough idea, but you want to be able to definitively explain to family and friends why this isn’t the magical solution to all of America’s transport woes. Today, we’ll dive into thermodynamics and examine what’s really going on here. Don’t worry—it’s easy! Plus, we’ll even try and figure out why someone might have built this in the first place!

No Free Lunch

Thermodynamics Is Not a Dirty Word

Let’s start by examining what we have here. We have the rear wheel of the car connected via a belt drive to what appears to be an alternator or generator of some sort. When it spins, it makes electricity. That electricity could of course be put to use charging a battery.

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That all makes sense. But does this mean we should all be putting generators on our EVs to drive forever? Well, no. Because no matter how much energy you get out of the generator, you’re spending more power to turn it using the car’s motor. It’s simply not possible for the generator to produce more energy than the Bolt’s motor had to spend to get it turning in the first place.

Let’s make a diagram. I’m using the terms “kinetic energy” and “mechanical energy” to mean basically the same thing—energy from motion. It’s a little simplified, but it should give you an idea of how this all goes down.

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Consider the car as if it were an isolated system, up on jacks. The battery runs the motor, which turns the wheels, which turns the generator, which charges the battery again. How much energy ends up back in the battery? Less than it put out!

It all comes down to the thermodynamic principle of conservation of energy. In very basic terms, energy cannot be created or destroyed. It can be converted from one kind to another, but you can’t create new energy.

This is why perpetual motion machines, free energy machines, and this “wheel generator” concept don’t work, and simply cannot work. If you had some kind of rotating machine which rotated forever, and you could get some kind of work out of it – say, by having it turn a generator – it would be creating energy. That’s simply not possible, due to the laws of physics. For the same reason, you can’t put a generator on your car’s wheel, recharge the car’s battery via the electricity generated, and drive forever.

In the case of the Bolt, the electric motor converts the electrical energy from the battery into motion. It accelerates the vehicle and spins the generator. The generator then turns rotational energy back into electrical energy again. All the energy coming out of the generator originally came from the EV’s battery itself. The generator didn’t make any energy, it just converted energy from one type to another.

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2013 Sema Chevrolet Zz5 350
An alternator puts out less electrical energy than it draws in kinetic energy from the engine. When you convert from one type of energy to another, you always face losses.

A further lesson that thermodynamics teaches us is that every time we convert energy from one type to another, we lose some. For example, a light bulb turns electricity into light, but we also lose some as heat. Combustion engines turn chemical energy into motion, but they also have losses through heat and noise.

It’s the same case here. The energy from the EV’s battery is converted multiple times, each time with some level of efficiency less than 100%. The EV’s motor doesn’t turn 100% of the battery energy into forward propulsion, and the generator doesn’t turn 100% of the rotational energy it harvests into electricity. Even if you feed its output back into the EV battery, you’d be getting less energy out of the generator than you were spending to turn it in the first place.

Simply put, turning the generator adds to the load on the vehicle’s drive motor. The EV’s motor has to work harder to push the car down the road because this generator is now on the back siphoning energy off the rear wheel. It’s thus drawing more energy from the traction battery than it otherwise would if there was no generator hanging off the wheel. Whatever energy you get out of the generator will be less than you’re spending to turn it.

But What About Regenerative Braking?

It is worth remembering, as well, that EVs have ways of turning rotational kinetic energy into electricity anyway. It’s called regenerative braking, and in itself, it perfectly explains why a wheel-attached generator won’t give you free unlimited energy.

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When an EV engages regenerative braking, it essentially turns its motor into a generator that is attached to the wheels. What happens? Applying the load of the generator to the wheels slows the vehicle down. It turns the vehicle’s kinetic energy into electrical energy to charge the battery. The generator can’t run without slowing the vehicle down. The electrical energy has to come from somewhere!

Naturally, there are some losses involved in the conversion. You can’t accelerate up to speed, then regeneratively brake, and get all the energy back. Some energy is lost in overcoming rolling resistance and aerodynamic drag, and some is lost through electrical resistance in the electronics and as heat through the motor. Similarly, as the generator converts rotating motion to electricity, there are more heat losses in the electronics, motor, and battery in turn.

2020 Bolt Ev One Pedal Driving And Regen On Demand Chevrolet Canada 1 16 Screenshot

Sure, you might say that this rear wheel generator would generate electricity if the vehicle was going downhill, using no battery power to accelerate the vehicle. Yes, that’s true. But the Bolt’s electric motor is already capable of acting as a generator in that case anyway. Plus, you’re still not getting energy for free. You had to spend energy to get the Bolt to the top of a hill in the first place before you could reap the energy by rolling back down.

Many Such Cases

There are all kinds of “simple” and “free” sources of energy touted in snappy little videos on the Internet. For example, one touted the idea of putting turbines inside water pipes to get “free” electricity from the flow of water. Of course, this would be completely pointless for a great many water pipes, as their flow is generated by the city’s water pumps. The pumps would have to work harder to overcome the resistance presented by the turbines, using more energy than the turbines could generate.

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Another example that is often bandied about is the use of an “HHO gas generator” to make a combustion-fueled car more efficient. This involves using a car’s electrical system to split water into hydrogen and oxygen gases. The mixture is then fed into a car’s intake to promote “cleaner” or “more efficient” combustion. Here’s the thing, though—even if the gas injection did improve combustion, you wouldn’t be getting out ahead. The energy required to split the gas would outweigh any potential energy you’d get back out of it when it passes through the engine.

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What’s Really Going On

The post shown at the start of this article is actually not the original. Somebody saw the photo of this vehicle and made an assumption about what was going on. Then, they spun their tale of free recharging that apparently Big EV was too stupid to implement.

The original photo was actually made by a user called rhinnaflor on Reddit, a full five years ago. Posting to r/whatisthisthing, they asked as to the use of this contraption. There are some compelling theories in the comments, and they don’t violate thermodynamic principles.

Belt contraption attached to the rear wheel of a Chevy Bolt
byu/rhinnaflor inwhatisthisthing

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AJ_Mexico pointed out that the Chevy Bolt may be a “dingy” vehicle that is typically towed behind an RV. With modern cars, it’s often recommended to tow them while switched on. However, this can drain the vehicle’s 12-volt battery over time if it is towed for many hours. The theory was that the system attached to the rear wheel was a simple alternator that had been hooked up to keep the Bolt’s 12-volt battery charged while it was being towed with its rear wheels on the ground.  This wouldn’t do anything for the main traction battery, and thus it wouldn’t improve the vehicle’s range. It’d just keep the 12-volt battery topped off, though you’d normally expect the Bolt’s traction battery would do a fine job of that already.

Naturally, this energy still isn’t free. The mechanical resistance of the generator would make the RV towing the Bolt expend more fuel—marginally—than if the generator wasn’t connected. Of course, there are easier ways to handle this task, too. One could simply fit a 12-volt solar battery tender to the Bolt, or hook up some kind of power line from the RV’s own supply. These would be much simpler.

Others suggest it might be some kind of instrumentation for data collection, but I’m not sure I buy that. It’s a very janky install, and the belt drive wouldn’t be super great for accurately tracking the wheel’s motion without slipping. It’d only be worse in wet conditions and when there’s any amount of suspension travel.

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The generator seems to be hidden to a degree by some kind of black tape. And what’s going on with that thing in the middle of the bumper?

If we zoom in further, though, this case gets more mysterious. There appears to be a fuel filler neck, or maybe some kind of cabling, tucked under the rear bumper of the car. Commenters speculated as to whether some kind of standalone combustion generator might have been installed underneath as a range extender, but the jury is out as to the truth.

It’s very difficult to definitively pin down what is going on in this image. Our best guess is that it’s some kind of wheel-powered electrical generator, but for what reason, we can’t say. If you’ve seen anything like this before, or you know the car in question, perhaps you could shed some light on the matter for all of us.

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Ultimately, I hope you found this article educational. You should have a better idea of why you can’t get unlimited range from slapping a generator on your car’s rear wheels. You might even feel confident enough to call out others who bandy about these long-disproven ideas. As much knowledge as there is out there on the Internet, free energy and perpetual motion ideas will seemingly never die. All we can do is call them out and have a chuckle when we see them.

Image credits: via Reddit, via AliExpress, Chevrolet

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Speedway Sammy
Speedway Sammy
21 days ago

I liked the Reddit theory that it’s a low buck approach to add supplemental rwd for slippery conditons since it supposedly had NY plates. Then somebody said the pic was taken in Florida. Then somebody said the trees in the background don’t exist in Florida.

Knowonelse
Knowonelse
21 days ago

It is the opposite of what everyone thinks! The filler cap is for a generator hidden underneath or behind that -drives- the generator thing which in turn -drives- the rear wheel. An auxillary motor to increase the range!

i3 Driving Indicator Fetishist
i3 Driving Indicator Fetishist
21 days ago

I’m amazed noone has ever spotted this Bolt again or the owner hasn’t come forward to explain it on some automotive blog.

Goffo Sprezzatura
Goffo Sprezzatura
21 days ago

It’s not that people are dumb- but life is hard. As our systems become bigger, and their operations more abstract, I understand how difficult it may be to understand their working principles.

Brynjaminjones
Brynjaminjones
21 days ago

This reminds me of a dumb thought I once had.

I did a degree in marine/mechanical engineering, and before I’d really learned anything (or engaged my brain) I remember wondering if you could put a wind turbine on top of a ship to generate some “free” power.

Thankfully I very quickly realized why this was so dumb!

Mikkeli
Mikkeli
21 days ago
Reply to  Brynjaminjones

Makes me think about those “directly downwind faster than the wind” discussions which thinking on too hard for dumbasses like myself is akin to staring at lovecraftian horror.

Adam Rice
Adam Rice
21 days ago
Reply to  Mikkeli

It was proven experimentally that you can run downwind faster than the wind.

Cheap Bastard
Cheap Bastard
21 days ago
Reply to  Brynjaminjones

As dumb as throwing up a sheet to move that ship.

Phuzz
Phuzz
20 days ago
Reply to  Brynjaminjones

A lot of small boats do have small wind turbines, but they’re mostly there to top off a 12V battery while the boat is moored up.
On something like a big oil tanker, it would still work to some extent, as the boat is so big the extra wind resistance would be barely noticeable, and most of the time the boat would be moving slower than the wind anyway. I’m not sure how much power you’d get out of them though.
In terms of using wind power to move a boat, sails* are still the most effective solution though.

*including proposed kite sails

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