Can you use an alternator on an axle to recharge batteries?

If you have a battery powered vehicle of some sort, can you put an alternator/generator or something on the axles to generate electricity to recharge the batteries the vehicle runs on? When the axle turns, the brushes pass over the coil generating electricity which is then routed back to the batteries thereby recharging the batteries. Please pardon the bad Paint drawing, but something like this.

Picture of Can you use an alternator on an axle to recharge batteries?
sort by: active | newest | oldest
Belt-drive the alternators, it'll be much easier to work with and repair.

Search for "regenerative braking" on wikipedia : http://en.wikipedia.org/wiki/Regenerative_braking
Sorry, the regenerative braking this was supposed to start with "See also" as it's a slightly different concept, but it's helpful in electric vehicles.
Tictazzto 7 months ago
Chittermlitem10 months ago

keep an open mind here, we do not need reminding of perpetual motion machines just finding advantages to extend the distance an electric vehicle can travel. To make a system more efficient is the basis behind any engineering project. With regards to the idea to design a alternative charging system using a alternator(s) or generator(s) to supplement the energy required for the batteries to have an extended run time using the axle as a supplier of energy is possible.

A lot of energy is lost to put a vehicle into motion. Picture this drivetrain for example...you pull the engine of your existing vehicle and couple an electric motor with the same horsepower as the engine had. Replace the exhaust, fuel, cooling, air and computer systems with a power pack and controller. The weight difference is negligible. Forget about how far you can travel on petrol compared to stored energy for a moment.

Briefly, the power losses from the electric motor (electric motor losses) through the gears in the transmission/transaxle (friction/mechanical are the same as with an engine) through the axles (more friction and heat) to rotate the wheels are all losses. Nothing in this scenario has changed from the petrol powered system except the electric motor is more efficient than the ICE.

To rotate the tires in this drivetrain system the power is transferred from the electric motor to the wheels with some percentage of power losses.

Who cares

There is a mechanical advantage acquired through the transmission/transaxle/rear end gearing to bring the vehicle to highway speeds.

Once you reach a steady velocity your object is now in motion.

Now is the optimal time to engage your alternator(s)/generator(s). Attach your alternator/generator (secondary) pulley to the inside of your vehicle wheels(rims) (primary pulley)

Basically run your generation system off the inside of your wheels(rims). If your vehicle wheels radius are 6 inches, your vehicle is moving at 100 km/hr you can expect the wheels are rotating at 1740 RPM. If your generator pulley has a radius of 1 inch you do the math 6:1 ratio. You can expect an arsenal of available energy and momentum to harness. The type, size and material of the pulley you use here on the alternator/generator is critical, you have to find the ideal fit between force (possibly movable force; an alternator that can move electrically or mechanically by hand levers, maybe mechanically using vehicle weight distribution or hydraulic brake pressure like a clutch slave cylinder and lever) against the wheel(rim) versus friction for your application.

There will be some losses from the alternator. Essentially this could also act similar to regenerative braking by increasing the magnetic field in the generating system. More pressure would also be required between pulleys (vehicle wheel and generating pulley) to prevent slipping between pulleys. There is a factor of motion down a hill to also consider, in hilly areas you could use gravity to aid you in your mileage increasing your rotor/stator field strength to your generating system going down hills. A more sophisticated system could auto detect these hills and hard braking.

gary01161 year ago

You might think about building your own solar panel for the roof. Much less work and the return is greater. This something I'm currently working on. Plus I would like to be able to use the 150 dollar deep cell battery from any auto or marine place. There are many different batteries. There are benefits and pitfalls to each.

The thing about drive alternators is you have to overcome the resistance of the alternators rotor. But if the car axle itself were the rotor and you were charging capacitors or using a diode to charge batteries, there would be no backfeed, no 'load'. To me this idea makes perfect sense, although I really have no idea/experience/knowledge to back that up.


The time has passed for an electric car. A car one may never have to plug in. The production of oil is all coming to a
close and gas and oil companies are spending 165 billion on exploration and
what are they going to do to our oceans that are in danger of dying
already. The price of oil may rise to
$200 a barrel or about $8 or $9 a gallon for gas or more and that is if the tax
on gas doesn’t go up. When solar panels
became popular to me in 1979 I was thinking of a car with solar panels on the
roof, trunk lid, and hood, then possibly on the tops of the fenders.

Over time we now have the greater black solar that
acquires power faster so we make a car like above and then add two freewheels
that will spin maybe a bank of hi-output alternators, then air-scoops turning
other hi-output smaller alternators. And if not too much drag hi-output
alternators working off the other wheels or axels, and if one just went to work
and back home one may never need to charge the batteries which would cost how much
on the electric bill??? We could call
it The Free Ride, and get permission and play Edgar Winters, Everybody Take A Free ride in
all new FreeRide.

i bought 2 of these little toy ysolar cars. These suckers GO! no batteries. Just a small gear on the shaft that drives a slightly larger gear on one side of the axle. http://www.ebay.com/itm/New-Wholesale-Kids-Adult-Solar-Power-Mini-Toy-Car-Racer-Educational-Gadget-Hot-/141363204837?pt=Baby_Toys&hash=item20e9e752e5 I'm thinking a scaled up version??? Why not?

Even if the resistance of the rotor isn't much, you also lose energy transferring power with a belt.

Unless the magnetic fields in the generator itself are working against the turning of the axle. Not sure how that works.

jeanga14 years ago
how about TWO batteries???... one used for the vehicle and its uses..

the alternator charging the unused battery.. then when you need power swap over to the charged battery then vice versa.. would that work ??/
jeanga1 jeanga14 years ago
I mean like a dynamo affect.. charging the not in use battery when your on the go instead of having to plug in to charge, or using a trickle feed solar panel to charge your unused battery while using the other fully charged one to power
I actually asked this question once and tried to build a little go-kart to test but had to much trouble getting a motor that would work for it.
I think that with proper gear ratios you could get a much larger return by using an alternator that is built for much heavier duty rather than a little <150 watt car alternator.
I once used one with bicycle gears to make the ratio changes and had it powering a light, but only as an experiment, it wasn't practical and the low speeds produced little amperage. The amount of extra bits made it unusable as a bike also.

Another thing to remember is that in most instances your alternator actually requires some electricity to run too. Something to do with creating the EM field inside it. So your not just losing on the mechanical side.
Zippomanonfire (author) 8 years ago
With this possible concept and with the regenerative braking concept, other than normal battery life expectancies and overuse etc., what would keep it from going 1000 miles on a charge if it is constantly recharging? Unfortunately Electronics isn't my thing. I don't get why if it recharges itself, you only get like 20-80 miles per charge. Lemonie- this might go a little into the perpetual energy thing.
You better watch out. You need voltage regulators and stuff but you can get speed controllers to do that.
Well there's no way you're going to get perpetual energy out of it. It's just not possible in the real world. Maybe in a world where everything is perfect and skittles fall from the sky but nobody ever gets diabetes... Every alternator/dynamo/generator you add to the system increases friction and weight, which the motor has to work against. Even more damning, the alternator doesn't reclaim anywhere near 100% of the energy your motor releases to turn the wheels. It's probably less than 20%. The extra energy is spent actually MOVING the car and through friction/losses within the system. Even the motor isn't 100% efficient, and I'll bet it wastes a good percentage of the energy it uses to produce heat and to fight its own friction. I'd guess conservatively, that an ordinary alternator from a passenger car would only increase the range of an electric vehicle by about 5-10%. I think this may top at around 20% using premium, lightweight alternator. Regenerative braking techniques have had claims of up to around 20% energy savings (which equates to a 25% increase in range)... but that's a best-case estimate and I do not trust it (and I even rounded it up just for easier math). I might even be wrong about the alternator's value. It might be that the alternator doesn't reclaim enough energy to compensate for the resistance it adds to the system. In that case, it actually helps to DRAIN the batteries faster. Yipee! Thats why, even if you have an electric vehicle, your range is limited. However, there are lots of things that can be done to increase range. 1. Improve the batteries: Technology still needs to catch up (but they're working on it) with this one. Today's batteries that are suited for this job are bulky and heavy... which hinder the abilities of the vehicles they power. 2. Reduce weight: Cut weight elsewhere in the vehicle and the motor will have less to pull, therefore less energy will be consumed. The challenge here is to cut back weight without sacrificing comfort or safety. 3. More efficient motor(s), gearing, steering, etc: More efficient parts use less energy (by definition) to do the same amount of work. In some cases it needs to be engineered, in some cases it just requires extra money. 4. Use of regenerative braking, alternators, to reclaim a PORTION of the energy that is lost.
That's awesome. Thank you for explaining it in detail for me. Thank you also for for not treating me harshly for my ignorance. I am mostly a tinkerer. I have lots of ideas for things with no clue how to get them to work, let alone how it works. I know a little bit about a lot and a lot of about very little. This is why I love Instructables. It helps satisfy my tinkering, and I get to learn new stuff too.
A little? You think? Try this. Take a alternator or dc motor and spin it by hand. Eventually it stops, right? That's friction losses inside the alternator. Now connect the output together so it's shorted out and try to spin it again. Little tougher, huh? That's because the physical motion is being converted into electrical work (in this case heating up the wire that's shorting it out). Every bit of friction and work and conversion to heat saps energy. By forcing the motor to run an alternator you loose energy (about 20% plus friction to get the power transferred). By adding the alternators you get LESS range because of these losses.
lemonie8 years ago
Yes, but please tell us this isn't some kind of "free energy" idea?

Zippomanonfire (author)  lemonie8 years ago
Nope, Just don't want to have to plug it in all the time/possibly extend the range.
so you're thinking have a motor drive you foward, and alternators generate power for you.

Only problem with that concept is that driving forward *costs* energy from the batteries, in exchange for motion.
The alternators *cost* energy from the momentum, slowing you down 'equally' - so you dont just get to keep the momentum AND the energy into the battery. When you use your alternator concept, the car comes back to a halt.

This is effective for recouping energy instead of putting it into heat in the brakes. - hence 'regenerative braking'

One time I hooked a small dc motor from a toy to a small dc generator, and it was pretty neat. Normally the motor would stop quickly, but this device would slow down much less quickly (would run for 2-3 seconds instead of less than half a second). This did not mean I was getting energy for free, just that it was recouping some.
You can use the motors to regenerate the batteries on downhills, some simple switching. L
Zippomanonfire (author)  lemonie8 years ago
Would it be just as simple as fabricating something like my above design? Or something more involved?