Intro: Pedal Powered Battery Charger
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... https://www.instructables.com/community/Generator-from-scooter-motor/ . I was asked to expand on it with an Instructable and so here it is. Have fun with it.