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.
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!
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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
Hum, that would have been the perfect article to link to another one treating the subject:
https://www.theautopian.com/thermodynamics-bernoulli-principle-and-carburetors-im-a-french-aerospace-engineer-here-to-teach-you-about-car-aerodynamics/
PS: yay for thermodynamics!
Hum, that would have been the perfect article to link to another one treating the subject:
https://www.theautopian.com/thermodynamics-bernoulli-principle-and-carburetors-im-a-french-aerospace-engineer-here-to-teach-you-about-car-aerodynamics/
PS: yay for thermodynamics!
All seems locigal. Thanks (heart emoji)
The only real “free” energies are the ones, where it doesn’t really matter if you take a tiny bit of it and convert it into electricity:
-Wind going all around the globe doesn’t care if a little bit of it gets slowed down by a wind turbine.
-Sun 8 million miles away (or something…) couldn’t be bothered if some of it’s rays hits a solar panel.
(People down on earth could of course be bothered by them and all “not in my back yard” like, and that’s why those solutions aren’t everywhere yet)
Yes, I’ve had a solar panel to top up my sailboat batteries for 14 years. About to install one soon on the rooftop of my “new” VW adventure bus also https://www.instagram.com/p/C8SYDi6iYtK
All seems locigal. Thanks (heart emoji)
The only real “free” energies are the ones, where it doesn’t really matter if you take a tiny bit of it and convert it into electricity:
-Wind going all around the globe doesn’t care if a little bit of it gets slowed down by a wind turbine.
-Sun 8 million miles away (or something…) couldn’t be bothered if some of it’s rays hits a solar panel.
(People down on earth could of course be bothered by them and all “not in my back yard” like, and that’s why those solutions aren’t everywhere yet)
Yes, I’ve had a solar panel to top up my sailboat batteries for 14 years. About to install one soon on the rooftop of my “new” VW adventure bus also https://www.instagram.com/p/C8SYDi6iYtK
Great write up.
It is however quite sad that it had to be written at all 🙂
In 1775, the Royal Academy of Sciences in Paris made the statement that the Academy “will no longer accept or deal with proposals concerning perpetual motion.”
Great write up.
It is however quite sad that it had to be written at all 🙂
In 1775, the Royal Academy of Sciences in Paris made the statement that the Academy “will no longer accept or deal with proposals concerning perpetual motion.”
Great write up Lewin.
Great write up Lewin.
Yeah, well what if you put a generator on each of the wheels and made four times the power? THEN you’d make it go forever! What do you say to that, Mr. Thermodynamic Smartypants? And I don’t need to read your highfalutin article – I did the research!
Signed,
Mr. Internet Guy (coming to you from the hospital for lack of a certain vaccination)
Yeah, well what if you put a generator on each of the wheels and made four times the power? THEN you’d make it go forever! What do you say to that, Mr. Thermodynamic Smartypants? And I don’t need to read your highfalutin article – I did the research!
Signed,
Mr. Internet Guy (coming to you from the hospital for lack of a certain vaccination)
They figured this out about 100 years ago just as IC Engines were becoming the norm. Detroit engineers figured out that if you strap a windmill fan to the top of the vehicle and run its axle through a set of reducing gears and clutch setup, the FAN ITSELF COULD POWER THE VEHICLE! Of course, BIG OIL got wind of it, so to speak, and had all of the information destroyed and started the rumor about something called ‘entropy’. They made it incomprehensible so nobody could argue against it.
(Torch, this is your prompt – run with it, man! Go!)
They figured this out about 100 years ago just as IC Engines were becoming the norm. Detroit engineers figured out that if you strap a windmill fan to the top of the vehicle and run its axle through a set of reducing gears and clutch setup, the FAN ITSELF COULD POWER THE VEHICLE! Of course, BIG OIL got wind of it, so to speak, and had all of the information destroyed and started the rumor about something called ‘entropy’. They made it incomprehensible so nobody could argue against it.
(Torch, this is your prompt – run with it, man! Go!)
As Robert Heinlein so eloquently had some characters state, “There ain’t no such thing as a free lunch”.
As Robert Heinlein so eloquently had some characters state, “There ain’t no such thing as a free lunch”.
This entire story could be replaced with the following:
“Entropy. https://en.wikipedia.org/wiki/Entropy“
For those educated in thermodynamics, yes!
But diving straight into entropy (and heck, exergy?) doesn’t help a general audience understand without a lot of ground work.
It’s a fun word, and a fun concept, but I prefer to take a more gradual approach to teaching thermodynamics.
You have to trick the students with fun analogies and candy first. Then you bring out the 2nd principle of thermodynamics and the math.
It is also a good book.
https://www.goodreads.com/book/show/122382.Entropy
This entire story could be replaced with the following:
“Entropy. https://en.wikipedia.org/wiki/Entropy“
For those educated in thermodynamics, yes!
But diving straight into entropy (and heck, exergy?) doesn’t help a general audience understand without a lot of ground work.
It’s a fun word, and a fun concept, but I prefer to take a more gradual approach to teaching thermodynamics.
You have to trick the students with fun analogies and candy first. Then you bring out the 2nd principle of thermodynamics and the math.
The 12V battery already gets power from the 66kWh traction battery on the bolt. There is no need for this.
This is most certainly some kind of datalogging or product development mule. Or a vehicle owned by a moron.
Yeah. I liked that explanation but it didn’t quite check out to me.
The 12V battery already gets power from the 66kWh traction battery on the bolt. There is no need for this.
This is most certainly some kind of datalogging or product development mule. Or a vehicle owned by a moron.
Yeah. I liked that explanation but it didn’t quite check out to me.
I get that this doesn’t work. However, as for range solutions, sometimes when I’m on my electric motorcycle I think about why can’t I just grab onto the car in front of me like Marty McFly on his skateboard
Yes! Make them do the work!
I get that this doesn’t work. However, as for range solutions, sometimes when I’m on my electric motorcycle I think about why can’t I just grab onto the car in front of me like Marty McFly on his skateboard
Yes! Make them do the work!
If I were king for a day:
– Post anything about perpetual motion, your punishment is 1 year of HS Physics, must pass with a B or have to retake it until you do.
-Post antivax crap? 1 year of HS biology.
-Post conspiracy theories? 1 year of World History and a course in Critical Thinking.
-Misuse or misquote ? A year of Literature.
-Post in all caps? A year of Composition and Grammar.
Other courses may be assigned as the transgression warrants.
I’d like to subscribe to your newsletter.
Like, a reeducation camp but for… actual education, not political punishment?
If I were king for a day:
– Post anything about perpetual motion, your punishment is 1 year of HS Physics, must pass with a B or have to retake it until you do.
-Post antivax crap? 1 year of HS biology.
-Post conspiracy theories? 1 year of World History and a course in Critical Thinking.
-Misuse or misquote ? A year of Literature.
-Post in all caps? A year of Composition and Grammar.
Other courses may be assigned as the transgression warrants.
I’d like to subscribe to your newsletter.
Like, a reeducation camp but for… actual education, not political punishment?
Has anyone pointed out that the original poster didn’t even get the Sherlock Holmes quote right?
“Elementary my dear Watson!”
So they don’t know any science, AND they don’t read, cool.
Not that this is the type of person to read or appreciate Sherlock Holmes, but come on man!
More like the kind of person who looks for scientific guidance in the works of John C. Holmes. Who, admittedly, was both thermal and dynamic, but not really in a relevant way.
Has anyone pointed out that the original poster didn’t even get the Sherlock Holmes quote right?
“Elementary my dear Watson!”
So they don’t know any science, AND they don’t read, cool.
Not that this is the type of person to read or appreciate Sherlock Holmes, but come on man!
More like the kind of person who looks for scientific guidance in the works of John C. Holmes. Who, admittedly, was both thermal and dynamic, but not really in a relevant way.
My favorite depiction of a perpetual motion vehicle was an image of a car being pulled forward by a giant cartoon magnet suspended from the car by a pole. Wile E. Coyote would have been proud.