How to Build a Bicycle Generator

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Picture of How to Build a Bicycle Generator
Using a few easily accessible parts, you can make a bicycle generator that can power various electronic appliances, such as laptops and batteries!

Materials needed:
Bicycle Stand
Bicycle frame
24V  DC scooter motor
DC-DC battery charger
A car battery, or something similar
DC-AC inverter
Wires for electrical connections and various bike parts and tools.

A multimeter might be useful to check various voltage differentials between different objects.

The specific hardware we used:
Motor: 24V 300W Scooter Motor
Battery: 12V 18 amp-hr lead-acid battery model 7448k51
Charger: Thunder 620 battery charger- 300 Watt 20 Amp
Inverter: 400 Watt inverter Model 6987k22

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Step 1: Bike Stand

Picture of Bike Stand
First you need something to hold your bike. You can either build your own bike stand or buy them. We used a bought stand for the back and made our own for the front. 

Buy a stand: These stands are especially nice for the back wheel because some of them are adjustable from side to side (right and left to the rider). This variation makes aligning the connection to the motor easier. 
Wazzupdoc1 year ago
I'm working on a similar project. I have a frame and will mount a wheel and gear on the back axle to power a bare rim. I envisage the rear rim as a pulley. I have an old clothes dryer drive belt I'll use to drive the generator from the rim, adding a few more RPMs. I'm playing with the generator portion now. I purchased a rebuilt alternator from Pep-Boys for about the same $ as your 24 volt motor. I'm leaning toward the alternator because of the plethora of automobile parts/adapters/interfaces to 12volts batteries and DC/AC Inverters. I have a solar trickle charger on board as well. Thanks for the inspiration!
abemckay (author)  Wazzupdoc1 year ago
Using a dryer belt sounds like a great way to get from the wheel to motor. Best of luck on your project!
ai4px1 year ago
Why not take the tire off the rear and run a big lawn mower V belt around the rim? You could probably run a 12 alternator from a car with that (and it has a V belt pulley on it!
abemckay (author)  ai4px1 year ago
That's what Wazzupdoc thought too; it's a good idea.
Jerz abemckay2 months ago

Keep in mind that the idle speed of a car engine is around 800-1000 RPM.
Using a car alternator directly driven by the rear wheel, you'd have to
be the flash to sustain any usable power.

peopleunite Jerz2 months ago

My bicycle's rear wheel sits on an axil. I get about 18 rotations with one full rotation of the wheel. That should give me plenty of RPMs.

anurag24794 months ago
working on this project
peopleunite4 months ago

I was hoping to make a direct drive, without the need of a pulley, but I'm stuck. I thought I got lucky with a good deal on a used bike resister. It's a bike stand with the rear wheel sitting on a cylinder (the resistance part is for exercise, but loosen it all the way and it's great for a generator). I also got a car alternator. The problem is the axis of the cylinder on the bike stand is about 10/32 of an inch wide, while the axis of the alternator is about 20/32". I was hoping to find a coupling at the hardware store that would screw onto both ends, but I guess it's too big a difference. Nobody carries anything like it. I would try searching online, but I'm not 100% sure of the measurements (done with just a ruler) let alone the thread width. The threads on the axis of the alternator look fine for something that big. I don't even know how they are measured. Any suggestions?

If I can't solve this, plan B will be to install a pulley. But it seems like an extra complication that could lead to more problems. I don't want to lose RPMs.

jayneil12348 months ago
hey do you think it is possible if i maximized the use of the bike im trying two use 2 motor to generate electricity one is with chain and the other is on the back wheel. do you think i can pedal the bike... i also seen on other post they remove the rubber on the back wheel and putted a belt connecting it with the motor. what you will produce more electricity?
myrepublic8 months ago
has anybody thought about replacing the wheel with a heavy flywheel? I know the engineering would be a little more difficult, but the rotating mass at speed would mean that it would continue to generate electricity after you stop pedaling. A speedometer mounted on the flywheel would let you know when you would have to pedal to speed up the flywheel to maintain optimum output, instead of pedaling continuously. Again this goes to extra cost, but one could add a second or more alternator and increase the electrical output. This type of setup is my goal.
ty.zardoz8 months ago
Some automotive alternators require that you supply voltage to "flash the field" before the alternator will produce electricity. Do a Google search to learn more about this.
stubbsonic8 months ago
This is exactly what I want to try to build. I have a trainer and could modify it. But I have a bunch of questions.

I'm leaning toward the car alternator version (because it would be cheaper). Unfortunately, I don't know what features to look for. Is there some rating about "torque" (?), in other words, should I be looking for something on how easy/difficult it is to rotate the shaft? Are there other specifications I should look for? I'm hoping to maximize power output (if I'm saying that correctly), so that I can get the most electricity possible for a reasonably cost.

Is a rim-drive possible with an alternator? Or is that too difficult to turn? I suppose I could find a used back wheel with gear cluster so I could put a belt on the wheel itself. I'm imagining this would be no easier to turn.

On the charger (or charge controller?) I'm guessing I'll need to make sure my choice of alternator & battery will affect what kind of charger I need. Should I choose this first and get other components to match or get alternator & battery first and then pick this last?

For the battery, I've seen something called "gas & coil" (optima) batteries that supposedly last longer. But any advice about which deep charge battery to get would be appreciated.
abemckay (author)  stubbsonic8 months ago
Thanks for your interest stubbsonic! I'll try to help the little bit I can:

I've never heard of "gas & coil" batteries, but you are looking for deep charge batteries, as you say. Google and wikipedia know more than I do.

I don't know that much about alternators either, but I found a study by these guys from MIT that may give answers your questions. They say alternators are usually rated for between 2,000 to 10,000 rpms. 
This is similar to the 2800 RPM rating of our scooter motor. I would imagine that using a back wheel (with some kind of belt) would give around the 3,000 RPMS you would want for an alternator, as it did with our motor. 

If you use an alternator, you may not need the charge controller. In that same alternator article, they say, "The alternator has a regulator that tries to keep the voltage across the battery at a steady 14.4V (the optimal voltage to recharge 12V car batteries). It does this by regulating the amount of current flowing to the field coil"

In our project the difficult-of-pedaling depended on the current which was in turn set by the charge controller. The RPMs and output voltage are similar for alternator and the motor/charger setups, so I'd imagine the third part of that balance - the difficulty-to-pedal - would be similar too. 

Good luck with your project, and let us know how it goes! Additions are always welcome, and we'll be sure to give you credit!

Thanks so much for taking the time to respond. This link is very helpful. For the rim-drive, there is a small rubber wheel that clamps up against the rim of the wheel (on the same part of the bike wheel where the brake pads squeeze). This little wheel has a diameter of roughly 9", so maybe there would be 10 revolutions of the alternator per one revolution of the bike wheel. My guess is that this would be comparable to having a big belt on the entire wheel rotating the shaft of the alternator.
TJ721 year ago
I'm building one that is powered by a 25cc 2 stroke from a weed eater...
Macattacku1 year ago
Yes tge charger is nice. I just wanted to point out u could save money by leaving it. Isnt yours low powered tho? Ive seen bike gens 300 watt+.
Leaving it out might have another issue; I'm not an expert on this, but when I built a bike generator & during early experimentation, I found out that it's possible to have power inadvertently backfeed from a charged battery. This made the pedals on the bike turn backwards! (and would have drained the hard-won juice from the battery.) I've been told that a diode needs to be included in the wiring arrangement. A diode is generally included inside devices like inverters/converters/chargers. I used an inverter (for its USB & 110v outputs) between the bike motor & the battery, and this made the project better, and solved the 'ghost pedaling.'
This looks good now how can I suddenly get fit enough to keep this Instructable at full power
Macattacku1 year ago
Let me just say that higher voltage will not damage a lead acid battery. With lead acid the only thing that matters is amps. You can charge it with 1000 volts dc if you want but as long as your under that 5 amp charge current the battery will drop all that extra voltage. The only time when charging at 1000 volts or anything high is a problem is when the battery is fully charged. You dont need a charge controler either all you need is a voltmeter. Charge it at whatever voltage yah like just stop when it hits 14.4 volts on the battery, meaning its full.
abemckay (author)  Macattacku1 year ago
We definitely agree, you can charge up the battery at any voltage above its current potential. However, our emphasis on not having a high voltage was more for the well-being of the charger rather than the battery itself. The nice thing about the charger is that it has circuitry that helps charge the battery better. Generally, it is recommended to charge Lead Acid batteries in three stages, depending on the current capacity of the battery: Constant current when the battery is low, topping charge (a sloping downward current with respect to capacity) while charging in the middle, and trickle charge, which is what you mentioned where it is important not to overload the battery while it is full. The charger that we bought managed all of that for us so we don't have to worry about our current and voltage, and helps maintain the charge and lifetime of the battery. Unfortunately, we found out the hard way that overloading the charger with a high voltage just from pedaling can break it (which was not easy to do-just be aware that the voltage being inserted doesn't exceed the manual's recommendation) and so that was our reason for including the voltage warning. Thanks for the advice!
Great idea! I just shared a link to it on Facebook.
Cyncha2271 year ago
PhilKE3FL1 year ago
Quick note: The "Thunder 620 battery charger- 300 Watt 200 Amp" is really rated at 300W 20A, not 200A (P = IV or V = P/I so 300/200 = 1.5 Volts which would be of no use to charge a 12 V battery!)
abemckay (author)  PhilKE3FL1 year ago
Good catch on that typo.
Joohansson1 year ago
Nice project! Would be interesting to calculate how many KWh you get of eating a 2000kcal pizza or something.
abemckay (author)  Joohansson1 year ago
Interesting thought. Here is a link to a website that guesses people are about 20% efficient. We would then need to test the efficiency of our generator. We have not yet tried it, and I'm guessing it would be difficult to measure the energy burned by the pedaler.
This is a great idea for couch potatoes. Hook the television up to it and only watch if you're pedaling.
I agree that a car alternator makes more sense than using a motor. I know the principles are the same, but it makes sense to use something that is purpose built if it's available.
I remember seeing this many years ago in a documentary on a war area. The power was constantly going out so this one fellow they followed around had done this. The bizarre thing (to me at least) was that the announcer talked about how the fellow would watch TV hoping for news that would indicate a possible end to the war so things would get back to normal and made no mention of the fact that the guy essentially plugged his TV into a bicycle.
What an innovative way to build a simple generator. The good thing I like about it is because it uses stuff that is readily available. With this you do not need to worry about long power outages and good thing it has an extra added advantage in that as you charge you are also exercising your body. Thank you for sharing this.

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