Why Don’t Electric Cars Have Alternators?

A common question we get about D.I.Y. Electric Car projects is “Why don’t you just add an alternator to charge the car as you drive?”

So, how about it? If fossil-fueled cars have alternators to charge their battery, why don’t electric cars just do the same?

To find the answer, we need to know how an alternator works and where the energy comes from.

An automotive alternator is a type of generator which creates Alternating Current (AC). A belt from the vehicle’s engine spins a pulley which is connected to the rotor of the alternator. On the shaft are either permanent magnets or copper wire coils with a small DC current flowing through them. The flow of current creates a magnetic field. As the shaft rotates, this magnetic field induces current to flow  in a matching stationary set of coils. Because the magnetic fields on the rotor alternate polarity (north/south), the direction of the flow of current induced “flip-flops” many times per second, reversing direction as well. We normally call that “Alternating Current”.
The alternating current is converted to direct current (DC) with diodes, and a voltage control circuit makes sure that the output voltage is appropriate for charging the vehicle’s 12V battery.

Where does the original source of energy for the alternator come from?
Scientists such as Galileo, Newton, and Bernoulli studied the natural world and came to realize that there are certain “rules” that are always followed. This eventually came to be known as the Laws of Thermodynamics.
According to the Law of Conservation of Energy, “Energy can neither be created nor destroyed; rather, it can only be transformed or transferred from one form to another.”

In the case of the alternator, the fossil fueled engine (connected by a belt and pulley) provides MECHANICAL* energy to the alternator which converts that energy to ELECTRICAL energy. The electricity isn’t “created”, it’s just some other form of energy which is converted. That means an equal amount is given up from the engine. The engine has to work harder and burns more fuel to be able to provide this additional energy.

Another important concept to remember is that the mechanical energy of the engine is not PERFECTLY converted to electricity. Some of it is converted to noise, heat, and vibration. Although efficiency is far from 100%, it’s still very useful to convert mechanical energy to electricity to charge the battery and run the electrical systems of a vehicle.

If an alternator works fine to charge a battery, why don’t we use one in an Electric Car?
The two main reasons are:
1) An E.V. doesn’t have an engine
2) There’s a BETTER device to use than an alternator.

Remember, the ENERGY that powers the alternator is actually the mechanical energy created by the engine through combustion of fossil fuel. An electric car doesn’t have an engine or gas/diesel fuel. Instead, it has an electric motor and rechargeable battery. We COULD use the battery to spin the motor to spin the alternator to generate electricity. BUT at best, we would simply be using electricity to make electricity. Even worse, there are still losses on the way. Conversion losses often show up as heat, but noise and vibration as well. Essentially, using an alternator powered by an electric motor, we could only ever make a smaller amount of electricity than we started with. (If we could create an equal amount or more, we would have a Perpetual Motion Machine.) However, we COULD make a different voltage. An electric car battery pack is typically over 300VDC, whereas we only need a 12V system for headlights, radio, and other accessories.

DC/DC – A Better Way:
If we only want to convert direct current from one voltage to another, there’s a much more simple and effective way to do it. That’s through a device called a DC to DC Converter. This is an electronic device which takes direct current at one voltage and converts it to a different voltage. It’s still not “free energy”. Converting to a higher voltage means also getting a lower current. Getting higher current means also getting lower voltage. Either way, it’s still the same amount of energy, minus losses, which show up as heat. Basic DC/DC converters dissipate the heat through a metal case. Higher power converters have heat-sinks, fans, or even active liquid cooling.

DC/DC Converters have several advantages over alternators. They are compact. They save weight. They are more efficient. There are no moving parts – no belts to replace, no pulleys, no bearings. That also means they are maintenance free.

If you purchase a DC/DC converter for your own DIY Electric Car project, keep in mind the input voltage and the maximum power. You want the input voltage it’s designed for to match the voltage of your battery pack. Many converters allow for a range of input voltage and are listed as so. For example, one might be listed as “48-96V IN / 13.5V OUT”. Power is rated in the maximum number of Watts that can be produced by the converter. In a car, you need enough power for the headlights, radio, and other accessories. This might be as much as several hundred watts. Remember to fuse the output of the DC/DC converter, and use appropriate gauge wiring for the output current. With rare exceptions, a DC/DC converter is always still combined with a 12V battery, just as an alternator is.

Electric Motor AS Generator:
Lastly, the AC motors used in commercially-built electric vehicles make excellent generators. But you still can’t magically create power while driving the car. Remember, we can only CONVERT energy from one form to another. There are still times when this is useful. Converting the KINETIC energy of a car to some other form (electricity to charge a battery, or heat of friction from traditional brake pads) will remove the kinetic energy and thus SLOW DOWN a moving vehicle. This is perfect when you want to slow down anyways! On an EV, we exploit this and call it “Regenerative Braking”. It’s a great way to recapture some of the energy used to originally accelerate the car, and increases the total efficiency of the vehicle.

In another scenario, a vehicle can be coasting down a large hill or mountain. The POTENTIAL energy is converted to KINETIC energy. In a manual transmission fossil fuel vehicle, the driver might downshift and use the compression of the engine to help slow the vehicle. In an electric car, the motor can charge the battery to do the same. It should be noted that the battery needs to be at least partly discharged to have a place for the electricity to go for regenerative braking to work. Better to live at the bottom of a mountain than the top of a mountain, as a fully charged battery won’t be able to accept any more charge through regenerative braking.

Alternators are neat technology, allowing us to convert mechanical energy into electrical energy. Similar technology is used on a large scale to generate electricity at power plants. Alternators work great for fossil-fuel-burning vehicles, but are complicated, inefficient, and high-maintenance compared to DC to DC Converters used on Electric Vehicles.

We hopes this give you a better understanding of alternators and electric vehicles for you to be able to work on your own Electric Vehicle Project.

-Ben Nelson and the 300MPG.org team



*A fossil fuel engine actually takes CHEMICAL energy (in the form of gasoline, diesel fuel, etc.) and ignites it, converting it to THERMAL energy which then moves a piston (LINEAR MECHANICAL ENERGY) which then turns a crankshaft (ROTATIONAL MECHANICAL ENERGY) which only THEN goes to the alternator via a belt. Energy is lost at every step of the conversion process.
Even worse than that, we need to get the fuel for the vehicle to start with. It takes a tremendous amount of energy to search for oil, drill for it, transport it, refine it, ship it to a gas station, and then finally get it in our fuel tank.
When we look at a total “Well-to-Wheels” scenario, a modern passenger car is possibly the most INEFFICIENT machine in human history.

{ 34 comments… read them below or add one }

1 Garry G May 5, 2021 at 10:25 pm

Why can’t the torque of spinning car wheels be increased through a seperate gearing mechanism which runs a seperate drive shaft to the alternator as the car goes faster ?

2 Vu Nguyen May 29, 2021 at 12:57 am

Well, if u guys worried about the drag of alternator when car moving then why not giving it a clutch? And attach that alternator to another smaller battery to supply lighting and something else.
The clutch only attach when not on gas the secondary battery is low

3 Roger Bradley June 3, 2021 at 11:18 pm

If the gear ratio to the wheel was such as it is on a ten speed bike or mountain bike then, the amount of energy used would not be a drag on the car. Just as you shift gears on a bike to reduce the amount of energy used in pedaling to make it easier, you can do the same on electric cars using an alternator connected to the wheels. I can’t believe that such high minded intelligent people like yourselves haven’t thought of the fact that to get smoother and more efficient use of gearing the wheels and motors of electric cars like that of 12 to 16 geared bikes will work!

4 Deplorable_Dog June 4, 2021 at 8:46 am

I wonder the same thing others do. Obviously an alternator cannot be ran off of the electric engine. However why can’t multiple alternators be ran off of the axle? And I am not saying that should make the vehicle never need to be charged off of a plug in source. However I will use the new Ford electric truck for an example. They say the range will be 300 miles with a 1,00o pound payload. So could alternators be used to increase the distance hypothetically speaking to 450 miles? I feel like one of the selling points of electric vehicles is range. I have one road trip I take at least two-three times a year that is 675 miles. My current Chevrolet Truck can drive 675 miles without stopping for fuel. I will not consider an electric truck until it can pull the same trailer, haul the same cargo and go just as far on one charge.

5 BobJ June 20, 2021 at 11:30 pm

Reading this discussion there was one suggestion maybe resolving this dilemma – what would happened if there where two separate batteries and some kind of alternator charging them separately one being use for drive when the other being charged and so one.
How come nobody is picking discussion on that?

6 Ben N June 28, 2021 at 9:37 am

This sounds a bit like having two glasses of water and pouring the water back and forth between the two.
You will never end up with more water than you started with. In fact, you will only eventually spill and have LESS water than you did originally.

With energy (whether electrical or other) you just have to think about where it’s coming from and where it’s going.
Moving it back and forth between two batteries does’t give you any more, and it’s even LESS efficient than using a single, larger battery pack.

7 John Jeffrey Pruett July 17, 2021 at 2:27 am

Ok geniuses why hasn’t anyone thought of a solar panel built into the rooftop not only would
Would it be nice looking as an accent done properly but it would absolutely increase the distance to which the car could travel.
“Solar Roof Panels concept Copyright 2021 GQ1981INC all rights reserved” my idea anyways just saying!

8 David Rosenbloom July 23, 2021 at 11:52 pm

Reading some of these comments helped me understand how some can believe trump won.
Listen people, engineers have thought about this far before you did. Alternators ARE amazingly easy to spin by hand… UNTIL you place a load on them, at which time they become increasingly difficult to spin.

Just stop for a moment and think about that 2000 watt (20 amp) Honda generator you used to go camping with. Why was it so heavy? Why did it need a two hp engine just to power the equivalent of 20 100 watt lightbulbs? Why do the engines of generators get larger as we ask for more output? Why do you actually hear the motor ramp up as you add more electrical devices or load to the generator?

9 Umed singh July 25, 2021 at 1:47 am

If we add a wheel (30kg )on the shaft of a 1hp dc moter and add a 6″ pully on same shaft with the rpm of motor is 1400 and the pully of 90amp dc alternater is 2.5″ what is the result

10 Ronnie Owen July 31, 2021 at 11:45 pm

There is a lot of debate here over why an alternator type technology cannot be feasible on an electric car. Yes, in conventional cars, it is the motor that turns the alternator, and when the alternator is under load the drag becomes more and more. However, there are very cost effective ways of using the wheels of the car to turn one or even multiple alternators by use of gearing, such as found on a ten, twelve or twenty-one speed bike. Some friends of mine and I have been experimenting with alternators wired together with fan blades attached to turn them with wind power to charge batteries to power a home. The biggest problem is that when under load, the alternators cannot be turned by normal wind power. So the solution we used was a very old and well utilized one, gearing. To accomplish this, we did have to go back to the pulley system instead of direct attachment of the fan blades. But we soon discovered that by utilizing a multiple gearing system (the 21 speed works the best) from a mountain bike, we only needed one fan blade to turn the alternators, (in this case 16 to provide ample power to charge 20 batteries), we were able to accomplish our goal. Now this would not eliminate the need to plug the car in when not in use, but it would increase the effective range of the car by 50 to 75% depending on the driving being done, such as stop and go versus highway, and on the other ways the battery is being used like for electronics and lights on the car. The tech is inexpensive, yet would provide a substantial boost in range which could mean all the difference on trips as well as could mean not having to end up stuck in a situation where you deplete the batteries and cannot charge (the equivalent of running out of gas.) this could also offset the difference in range if you were towing or hauling something. The same gearing tech could also be very effective by allowing the electric motor in the car to turn the alternator, but by not utilizing the wheels and using the motor the effective increase does drop to only a 25-45% increase in efficiency. But that is still an increase in range none-the-less.

11 Ben N August 1, 2021 at 10:13 am

It’s not that an alternator COULDN’T be used on an electric car. It’s that it could NOT be used to extend the range, as ALL the energy is coming from the battery pack – it’s would just be going to an alternator in a very roundabout way. The load of the alternator would create additional drag on the vehicle, greater than any energy it would be able to create.

For something like a wind-turbine, the source of energy is EXTERNAL – it’s the power of the blowing wind. The generator portion of a wind turbine creates resistance to turning the blades, which is a big part of why wind turbines generally need some particular minimum wind speed. Most commercial wind turbines DO use gear reduction.

Gearing does NOT create energy – it simply trades speed for torque, or vice-versa.

In the old example of a dynamo on the front of a bicycle which powers a light, the bicyclist must PEDAL HARDER when the dynamo is engaged as it’s the bicyclist himself who is the source of the power to run it.

12 Autumn August 8, 2021 at 1:39 am

I have the same question Garry. Why can’t belts on the tires generate power to an alternator that would go to a controller that would then charge 24v (two 12v batteries in series) to an inverter that then could make a plug that could plug the car in that could give it a constant charge? This is what I have pictured. I was hoping this question would be answered here. I mean the breaks could cause an issue, but I’d say the belts would need a release that would remove the belts from the tires when the breaks are applied temporarily stopping the alternator charge until the car is in normal motion again. And Why can’t the cars have solar panels on the roof going to the same controller keeping help in a constant day charge?

13 Ben N August 9, 2021 at 9:21 am

What powers the wheels?
The energy has to come from the battery to spin the wheels to then (in a roundabout and inefficient way) charge the battery. You can’t charge the battery with the battery. There’s no gain.

On the other hand, solar panels CAN charge an electric car! The external source of energy is the sun. The issue is that solar panels tend to create a small amount of power compared to that which the car uses. So, it’s totally possible, but just not practical.

14 Negentropy August 11, 2021 at 10:58 am

You should check out the MEG, or Motionless Electromagnetic Generator, created by a team of accomplished engineers, including the celebrated nuclear physicist ret. Lt. Colonel Tom Bearden – see website. Newton’s quaint 2nd “Law of Thermodynamics” is not a complete understanding of energy, and certainly not a law. In fact, the opposite of this “Energy Conservation” ideology is true in certain cases.

What we have been taught about electrical generators applies only to closed systems, or all available alternators and generators which endlessly manifest and destroy a dipole. Very inefficient way of harvesting free electrons! Why not create a dipole and leave it open? Then you have expended energy once, and diverted the free electrons down an alternate flux path without disturbing the primary. Yes. That concept is proven and independently confirmed by many others, including a device called a ‘Bi-Torroid Transformer’ by Thaine Heinz having 2 secondary coils and a primary. Very clever!

You see, we have simply not paid attention to the math that E.T. Whittaker exhaustively showed us in 1903. His work was an extension of the famous Maxwellian principles of Thermodynamics, which gets misquoted all the time due to omissions. Thanks Lorentz, you turd. Unfortunately, engineering and math like this goes above most people’s heads so we just accept the party line explanation of why we can’t do something. Simply put, you can. All you need is to do some research and stop accepting no for an answer.

Open systems are the future and the full understanding of energy cycles must include the reciprocal to Entropy, which is called Negentropy. Yin to the Yang. Open to the closed systems. Now that you know, please check out my claim and you will see the hoodwink our corporate overlords have foisted upon us in the name of dollar$. #TeslaKnewWeWouldFigureItOutEventually
#ZenneckWave #SpaceTimeConnundrum

15 David Sands August 15, 2021 at 8:25 pm

Many of you are missing a few key things:

1) When the accelerator pedal is pressed, all energy is coming from the battery. You can’t capture that energy to put back into the battery. Gears don’t magically add energy. Whatever you gain in input torque you lose in output rotations. The more gearing you use to make it easier to turn, the less actual current you will get out of it per turn of the initial gear. And energy would be lost in the process by friction in all the gears, belts and other moving parts. So the energy needed to maintain or increase speed would increase to account for any energy removed from the system to turn the alternator. You’d draw MORE extra energy from the battery just to maintain or increase your speed than you would get back. You will always end up losing energy (and therefore lowering your range) on this. You can’t get around that. (And that’s ignoring all the extra mass you would be adding, as Ronnie claimed he needed 20 alternators to even register enough current to even charge a battery)

2) You might be thinking ‘Okay, but what about when you take your foot of the pedal to slow down?’ The engineers already figured that out. This is what regenerative braking is. As soon as you take your foot off the pedal, the motor disengages and uses the rotation of the wheels to spin the motor backwards to work as a generator, slowing down the car in the process. This process isn’t that different than how an alternator works. But it ends up being more efficient because it doesn’t add extra moving parts.

To summarize: The spinning wheels are either spinning because of battery power, in which case adding an alternator would just be draining the battery some extra amount just to put less energy back into it, which would REDUCE the range. OR, the energy is already being harvested by the regenerative braking system in a more efficient manor. If you think there is some other source of energy that would spin this alternator, I’d be curious to hear about it. Any sort of wind turbine would cause more energy consumption by adding drag than you could get out it.

16 Dtuttle2000 August 25, 2021 at 7:57 am

Ben N., finally someone on here that actually understands physics.

17 Beñ m September 1, 2021 at 10:40 am

They have the technology for the constant charge to make it 100% self-efficient they just don’t want to use it. not yet. It’s all about the marketing God forbid for them to make a vehicle that doesn’t need charging or fuel. The bigger picture is that kind of vehicle will be a problem for Big industry and marketing.

18 Ben N September 1, 2021 at 10:42 am

Who are “They”? If “They” are hiding something, wouldn’t it be a big conspiracy and hard to hide the technology? Why haven’t backyard mechanics built such things if it’s possible?

19 Patrick September 24, 2021 at 10:26 am

Pls my question is relating to the topic discussed but not the case study.
If I’m generating AC using an inverter from a 12v battery and then, using a battery charger to charge another battery from the generated AC in the presence of load. Is such system effective?

20 Scott Munyon September 27, 2021 at 8:44 pm

I’ll figure it out and get back to you all. Thanks!!!

21 Kevin October 26, 2021 at 8:16 am

Hydrogen power I suspect is already being an alternative after all money’s are taken from battery power!

22 bob November 2, 2021 at 5:34 am

Air is the answer to the question you need to put fan on alternater and use direct air from front of car this would not fully charge it but would give more miles.

23 Ben N November 2, 2021 at 8:14 am

So adding MORE air resistance makes the car more efficient?!

24 Ben N November 2, 2021 at 8:15 am

No. You are simply moving energy from one battery to another, and there are losses along the way, so the second battery doesn’t even get charged as much as the first battery loses.

25 Ben N November 2, 2021 at 8:27 am

There HAVE been electric cars with solar panels in the roof!
The important aspect of it is that the sun is an EXTERNAL source of energy, and the solar panels bring that energy into the electric car’s battery and motor system.

In general, cars us a LOT of power to move about, and solar panels need to have a large surface area (and be pointed straight at the sun) to produce large amounts of power. So, a typical America-style car is NOT going to get a large portion of its energy from solar panels on the roof, but it certainly could get some.

Probably the best known solar cars are ones that have been in engineering competitions. Such as the World Solar Challenge

I’m sure we’ll eventually get some mainstream electric cars with solar built-in on them sometime soon. A company called Lightyear One is working on such, but it’s unknown how far along they really are on their goal of a car that is COMPLETELY charged by built-in solar.

In the mean time, solar panels on a person’s house or garage can charge an electric car AND power the home.

26 Creative Curt December 2, 2021 at 8:15 pm

Why can’t you have a pulley attached to the axle and a pulley to a generator with a belt that charges the battery while you’re driving? As long as its moving its creating electricity?

27 Ben N December 2, 2021 at 8:19 pm

You could – it’s just that for every bit of electricity being generated by your belt and generator, even more electricity has to come from the battery to push the car down the road.
Generators are NOT free energy – they take MORE work to turn, and that energy has to come from somewhere. In the case of an electric car, it’s coming from the main battery.
So, you just end up draining the battery more, NOT charging it up!

28 Paul Rodgers December 11, 2021 at 11:25 am

Imagine plugging a flashlight into the wall that is being charged by the light turned on with solar power. There is a way this works and I will never tell you guys…😐

29 howard January 5, 2022 at 5:54 pm

guys. think you make it like an alternator weighs 4500 lbs that are no drag or cost it would far more costly to constantly to charge the car an alternator use will make the purpose of going to a charging station less next to zero because that part is covered by the alternator in which is far overlooked and it’s less costly to replace than to replace any component of an EV if you worry of a heat issue just add a water pump to it to pump cooling fluid to prevent overheating by tubes basic tech stuff in short dint make excuses to eliminate basic things and that can be USEFUL.

30 Terrigenous March 12, 2022 at 6:02 pm

I have made a car very similar to a tesla car.. And it is about 8 years old.. Does pretty much same things as a newer car, other than auto pilot. But when the battery is down to 20% after 274 miles, a small 15 hp gas engine starts with a big alternator and recharges the battery. Takes roughly an hour while driving and sitting about 35 minutes. The gas engine can run for 8 hours on 2 gallons of gas. So years I can travel little over 2000 miles on 2 gallons of gas. Once battery is at 98% the engine shuts off and car runs completely on battery until it’s down to 20% again. I can also tow a small camper with this setup.. However towing reduces the times the battery needs recharging more often.

31 Mike B March 21, 2022 at 12:11 pm

There are some really interesting ideas here. When it’s eventually cost-effective to implement supercapacitors at scale, we may very well see an alternative to regenerative braking for charging capacitors -one that’s conducive to highway driving and fleet vehicles traveling long distances. It may even look just like some of the proposals above, or a combination of them. The equation changes when we factor in the efficiency of delivering power. Instantaneous power to the motor -without loss- delivered via supercapacitor during periodic moments of heavy load could be exactly the solution EV trucks need for practical work and fleet use. If the efficiency gains can exceed the enwrgy cost to charge those supercapacitors, it will lead to a more efficient allocation of energy from the primary system when say, passing or climbing a hill while towing a load. The supercapacitors would not suffer the waste and inefficiencies of the primary system, increasing what can be achieved with the same energy cost. So in such a situation where we can use stored energy more efficiently, it might be advantageous to do what otherwise would seem like a net loss. Advancements with graphene for recharging supercapacitors could change everything. In the city with regenerative braking, supercapacitors couls make an enormous difference in range. As of now, not so for highway driving.

32 Ben N March 21, 2022 at 12:46 pm

Do you have some more information posted somewhere on that project? I’m sure we would all love to see it.

33 Paul April 11, 2022 at 9:38 am

One question I got was using a brushless generator, say on the rear wheels with a small axle. The magnets don’t have to be that big, and have very very low friction bearings or something, as just want to extend the range. This would be on top of the high output regenerative braking. I actually think that is doable, even if only extends 5%, these days would get you another 10-20 miles. Thoughts?

34 Ben N April 12, 2022 at 10:26 am

It doesn’t matter where on the car you put an alternator/generator, or how small the magnets are. Energy has to come from somewhere. In an electric car, it comes from the battery.
Alternators are a LOAD! They USE power (mechanical) and convert it to some slightly smaller amount of power (electrical). In a gas car, that means it uses gas to make electricity. In an electric car, you would be using electricity from the battery to make some smaller amount of electricity (due to inevitable losses) You do NOT come out ahead.

Regenerative braking is a neat trick because it converts the energy of the mass of the vehicle already in motion to electricity. Since it’s using energy to convert, it slows the car. Keep in mind that the energy that’s created there originally came from the battery – when the car accelerated – and that not as much is ever recovered as was spent to get the vehicle moving in the first place.

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