Pedal Powered Battery Charger




About: I have a project at on making x-rays. I post some of my projects in a blog on the MySpace page.

Introduction: Generate enough power to charge 12 volt batteries.

There are increasing numbers of people who are behind on their utility bills and could have their electricity cut off. They need something to help reduce their dependence on the electric company, something that can also supplement wind and solar power generation. This may help.

This is a project to generate practical amounts of electric power by using bike pedals. I ended up using three stages of chain to drive a DC motor as a generator and charge a car battery. The use of chains turns out to be durable and efficient. The various sprocket sizes let you choose the speed that you need for the motor you have.

I used a discarded 24volt scooter motor in this project, but this thing is flexible enough to work with lots of different DC motors.

Everything in this project was from stuff I found in the course of my dumpster diving, including various bicycles and bike parts. I have no prices for any of this.

Above, you can see a photo of my contraption. Find a good, comfortable seat for this, otherwise your derriere will get quite sore.

Step 1: Materials Needed

1. Scooter motor with it’s chain and sprockets.
2. Cheap jumper cable.
3.  Two rear bike axles with nested sprocket.
4. Two small hinges.
5. Two bike frames.
6.  Two metal brackets.
7. Plywood. 16“x20“x5/8“ and 11“x16“x5/8“.
8. Lumber. two 2x6x18“, two 2x6x15“, one 2x4x28“, and one 1x2x14“.
9. Mounting board for the motor. About 6x6x3/4“
10. Two bike chains and chain tool.
11. Diode. 100 volt, 3 amp will do.

Absent a scooter motor, you could test various other motors by spinning the shaft with an electric drill while monitoring and comparing outputs.

Step 2: Find a Junk Adult Sized Bike.

Once you have the bike, remove the front and rear wheels. The front wheel is not needed. Remove the tire, rim, and spokes from the rear wheel.

I used wire cutters to clip the spokes. They are tough and hard to cut. Another method may be easier. Photo 1 shows a closeup of the spokes gone.

Step 3: The Stand.

Devise a stand for the rear assembly using the plywood and lumber. Photo 2 shows what I put together. The C-clamp at the top is there as a handle and is not necessary.

I used drywall screws to put it together, just in case it was necessary to change it.

Step 4: The Brackets.

Fabricate the L brackets and attach them to the rear of the bike. Then attach the brackets to the stand using screws. Photo 3 and 4 show this. Test the rear axle to make sure the chain does not jump from the sprocket you want to use.

I used some scrap sheet steel to make the brackets.

Step 5: Second Chain Assembly.

Cut the rear tubing from a child’s bike and mount it on the hinged platform as in photo 5. The perforated strap in the photo was not needed. The white wire is there to pull the gear into alignment.

The two hinges are under the platform, out of sight. The weight of the motor assembly was not sufficient to keep the chain tight. The straps are a failed attempt to fix that. I ended up using a 1x2 to wedge the frame tight. This wedge board is visible in Photo 2.

Step 6: Large Scooter Gear.

The large scooter gear that I have was able to fit over the spoke ring on the second bike axle. There was minimal grinding required for a tight fit. I use four bolts to keep it together, as shown in photo 6 and 7. Incidentally, the small scooter gear is on the shaft of the motor.

The chain tool will be used to make a bike chain that links the two rear axels, as shown in photo 4 above. The chain tool I have is shown in photo 8.

Step 7: The Second Rear Axel.

Install the second rear axel and make a chain that will fit. Test the running of the chain. You need to make adjustments so the chain runs smooth and won’t jump to neighboring sprockets when tension increases. Photo 9 is a top view showing my chain positioning.

Note: There are slightly different chains and sprockets out there. Make sure you get matching ones, otherwise the friction and roughness will be high.

Step 8: Mount the Motor.

Cut a 6x6x3/4 inch board to mount the motor and a terminal block for the diode and connections to the battery. Devise a clamp arrangement so the position of the motor is adjustable to tune the chain tension and alignment. See photo 10.

To make room for the chain, you may have to notch the board as I did in photo11.

Step 9: Adjustment.

I used part of a discarded jumper cable to connect from the terminal block to the battery, attaching part of the cable to the frame to avoid bending the connection.

You will probably have to adjust the angles and position of the gears to keep the chains running true and in their proper place. Photo 12 is another angle.

Step 10: The Output.

The diode, which came from an old TV set, is probably three amp at about 100 volts. It is just a blocking diode to prevent the battery from running the motor. The output from my motor is opposite in polarity from the leads. That is, the red lead is negative.

As you increase pedaling speed, you generate more power and it becomes more difficult to keep up the effort. I was able to generate 5 to 6 amps at about 13 volts for about 30 minutes before taking a break.

Photo 13 shows an oscilloscope trace of the top 10% of the output showing that it is pulsating direct current. The pulse rate depends on the rate of speed of the motor shaft. You have to adjust your chains to give the most comfortable pedaling rate for the output you want to produce.

I have added photo 14 to show the diode on the terminal block.

In answer to the questions: Will this brand of bike work?, Will this type of motor work?, Will this part or that part work? The answer is... I dunno’, you will just have to try it. I have not tried other motors because this assembly has been working so well.

There is no video because I don't have the experience or software to make them.

This was an evolutionary project that started as a posting of an idea... . I was asked to expand on it with an Instructable and so here it is. Have fun with it.



    • Big and Small Contest

      Big and Small Contest
    • Toys Contest

      Toys Contest
    • First Time Author

      First Time Author

    19 Discussions


    2 years ago

    That's just about the coolest terminal block I've ever seen.


    6 years ago on Introduction

    Nice Job. I wonder if you could do the same for the front and utilize the other sprocket atached to the pedles? Well done, we need more of these. Plus it will help us get in better shape.

    2 replies

    Reply 6 years ago on Introduction

    You could indeed find a way to use the front.... but, the work you do would be distributed among two motors, and thus reduce the output from an individual motor. It would also increase the friction in the system, due to added chains, and reduce your output.


    At the end of 2012 I was at Occupy L.A. for 3 weeks (I had a place to live, and I left before on the last weekend, as soon as the LAPD notified everyone we could be arrested from that point forward). Anyway I was there to watch history and shared a tent with a friend who was writing about it for the Examiner. Batteries were the bane of our existence; I killed 2 cell phone batteries totally dead every day, then there was the issue of writing on our laptops. The organizers did manage to provide decent wi-fi, though, at least up where the media tent was.

    There was plenty of voltage from the solar panels they had set up but not that much current. Plus the power provided by the organizers had already been converted from the DC solar output to 110 AC, the bulk of which was used for laptops, etc., so taking that AC and plugging a laptop's power supply in to revert to DC was probably pretty wasteful (I never did the math, because no one could tell me the efficiency of the DC to AC conversion).

    Anyway, this is exactly what we needed and I mentioned that, repeatedly. Unfortunately electric bicycles hadn't really taken off yet - the few that were on the market were prohibitively expensive. There was a ton of free labor available, also 50 or 60 bicycles, some of which weren't fully road worthy anyway. I even spent half a day walking around where the Asian toy & electronics importers were in downtown L.A. looking for any kind of effective kinetic-to-electric charger. I had seen those things they were shipping with the $150 laptops to Africa during the "one laptop per child" initiative, but I couldn't locate anything like that, only items I regarded as useless; turn a crank for 5 minutes to make a 30 second to one minute phone call.

    In the end we wound up doing most of our writing from a local Starbucks and I charged my phone batteries at the same time. But I still wound up running both batteries completely dead every day, the absolute worst of all battery management strategies.

    On a side note, despite all of the negative forces both within and without the occupy movement (including professional provocateurs who were very good at their jobs), it was a core group of 25 or 30 serious people that kept that encampment going for months. Of course you never saw any of those people on television, only the 'fringe' elements.


    4 years ago on Introduction

    Thanks for sharing. Follow plus favorite. Cheers....


    5 years ago on Introduction

    Hmm, could this be rigged to an electric converted bike to charge the battery while peddling?

    1 reply

    You would need to drive two sets of chains. One chain to drive the rear wheel in the normal fashion, then another set of chains to drive the generator at the high rotational speed that it requires. The energy you produce would be divided between the generator and your forward motion.


    6 years ago on Step 10

    Why not use the Alternator from a car?

    They can be had for pretty cheap at the junk yard.

    They come with diode packs and are designed to charge batteries.

    You can run them with belt pulleys or be modified for chain pulleys.

    7 replies

    Reply 6 years ago on Step 10

    I tried an alternator once and found it takes much more effort to generate the same power. The alternator will draw power until you get it running about 3000 rpm, at which point it transitions to generating more than it uses.

    Alternators do work well enough when run by a small gas engine.


    Reply 6 years ago on Step 10

    I would have to see a side by side test on that. The using more power does not make sense. An alternator creates a 3 phase AC out that is converted to DC and then is run through a regulator to save a battery from damage.

    Besides if there was a 3000 RPM issue then switch to a diesel alternator or change the gear ratio.


    Reply 6 years ago on Step 10

    Remember, there are no permanent magnets in car alternators. The rotor is an electromagnet that receives power from the battery through a pair of slip rings. That power must be restored by increased effort at the petals.


    Reply 6 years ago on Step 10

    Hmmm I guess I would have to build a permanent magnet version then. I've seen plans for them online and are better than using a DC motor.


    Reply 6 years ago on Step 10

    On a solar power site, I found modified alternators for sale. The electromagnet rotors were replaced with a permanent magnet rotor. I don't have the link.


    Reply 6 years ago on Step 10

    I hope you don't take me wrong I honestly like your plans.

    I just think differently that most people and I had remembered that Tesla had used 3 magnets on an equal lateral triangle spinning on a shaft to create AC power. So I was shocked to learn that Alternators have brushes.

    I have seen homemade 3 phase permanent magnet wind turbines. I often forget that manufacturing designs often don't make any sense.

    I do apologize if I come off as being argumentative, I am not trying to be.

    I just had remembered from design that using an electric motor as a power source was an inefficient method. Effective yes efficient no.

    I am just always looking to eek out the last drop of power that I can from something like this.

    Thank you for entertaining my questions and inquiries.


    Reply 6 years ago on Step 10

    No problem.
    I have found great variation in how well a motor generates power. One way of testing a motor is to short the leads and spin the shaft. A shaft that becomes hard to spin will indicate a good generator. In some cases, after connecting one motor to another and spinning the shaft, you can see the second motor working from the output on the first motor.

    If you want AC, use a stepper motor. Old printers, scanners, and copy machines often have stepper motors. It would be interesting to connect the output of a stepper motor to the oscilloscope and see how the voltage and frequency varies with shaft speed. Use a variable speed drill or Dremel tool to spin the shaft while monitoring output.