Today I would like to show you how to build a very cheap yet working bicycle generator. My idea is not competing with a store-bought “dynamo”, but instead teaching you a fun project made from trash (and some of the science behind it).

Step 1: What’s a Generator and How It Works?

A generator is a machine that converts movement into electrical power using a principle called “Electromagnetic Induction”.

Every time when electrical current travels through a conductor (let's say a piece of wire), a magnetic field forms around that conductor. You may ask “If that’s true, why my cellphone charger cable isn't sticking to metallic stuff right now? Well, the strength of the magnetic field is proportional to how much current is flowing through the conductor, and in the case of your charger the current is negligible. But with more powerful currents the field is significant enough to, for example, lifting industrial metal scraps with a crane.


Electric field running through a conductor. Result: Magnetic field is produced around the conductor

Step 2: What’s a Generator and How It Works? (cont.)

The principle also works backwards. If you move a magnetic field near a conductor, an electrical current will be induced in the conductor. Now, by “moving” it’s equally valid to physically move the magnet or just turning the magnetic field on and off repetitively.

So remember:

Moving a magnet near a conductor. Result: Electric current is produced on the conductor

Step 3: Real World Generator Example

No matter if you buy a old squeaky “Bottle Generator” like the one on the attached picture, or a "hub generator" (the beautiful noiseless alternative), the principle is the same. The movement of the spinning wheel spins a magnet, which is in close proximity with a wrapped coil of wire.

The interesting thing is that a toy motor can also be used as a generator. The motor converts electricity into magnetism, and magnetism into movement, right? Well, spinning the motor will produce electricity. Same principle, used backwards: Moving the magnets inside the motor induce electrical current.

Step 4: Enough Theory, Let's Make the Generator Now!

As you obviously guessed, we will need a small electric motor. I got my motor from a burnt hair dryer. You can get yours from an old toy, it doesn't really matter if the device is broken as long as the motor still works.

Step 5: Preparation

This motor has a couple of ventilation openings on the sides. This is for refrigeration, but I'm closing them to avoid dirt and crap from the road entering the internal parts.

Edit: Don't try to re-use motors from computer fans because they use a slightly different working principle. The same applies to step Motors from old printers.

Step 6: The Poor Wheel

To transmit the rotation between the wheel and the motor I'm going to use a rubber wheel from a LEGO set I stole from my friend Juan when we where kids. Sorry pal, I'll someday return it.

Note: I strongly recommend you to find a creative alternative to the wheel. The truth is, a LEGO wheel is not designed to withstand the loads of a bicycle ride and will fail soon.

Step 7: Adapting the Wheel to the Motor Shaft

You can attach the wheel using super-glue

...but I just liked to show off my new set of drill bits, so I inserted a retaining screw, taking advantage of a flat face on the motor shaft.

Meh, this was a total overkill for a wheel that will not last long. So forget it, just attach the wheel with your favourite super glue!

Step 8: "Spring" System

The bicycle rims tend to be non-aligned, and you must provide a method to maintain a constant pressure between the generator wheel and the rim no matter of the bumps or depressions.

A commercial generator is mounted on a spring loaded structure, but since we are working with dirt here, a piece of foam will do. Obviously you are free to find a more decent method after you finish the experiment.

Step 9: Fastening the Assembly

Since this is a somewhat disposable arrangement, I used zip ties. Find a balanced point where the motor doesn't fall from your bicycle, but there's enough pressure from the foam to keep the LEGO wheel spinning against the rim. Don't get frustrated if you don't nail it at the first time.

Step 10:


Nah, is really is 12 volts under load. But the current is decent enough to light a small bulb from a car interior light.

Step 11: Slight Improvements

You can focus the light using parts from a flashlight

Step 12: No LED for Now, But Coming Soon!

You can see I used a small 12V, very inefficient, incandescent bulb.

After building this prototype the next natural step would be wiring it up your much more efficient and good looking existing LED lights.

But I recommend you to wait, because some considerations must be taken. For example, depending of the type of motor you pick up for the experiment, your generator will end up producing DC or AC current. You should also provide a way to regulate how much current goes to your LEDs.

Step 13: DC Vs. AC Current and Voltage Regulation

If you see a battery, the terminals are labelled with + and -, and this arrangement is maintained during the life of the battery. This is called DC, or Direct Current. But other power sources, like the outlets at your home, provide current that is constantly changing sides (technically called "polarity") each second.

AC or Alternating current is very useful for power transmission, but unfortunately your LEDs will not like it. Since they only glow if polarized on the correct way, they will blink like a party strobe light every time polarity is reversed. They can withstand this condition for some time, but inevitably they will burn out.

Even If you are lucky and your generator produces DC, there's another problem. The output of your generator will vary proportionally to the wheel speed. That means that if you go too fast, the voltage output will also sky rocket. Brightness of your LED will increase until again, they inevitably burn out.

But fear not: we can fix all of this using some cheap electronic components on a next instructable.

Step 14:

<p>Thank you very much by your comments guys!</p>
<p>very cool</p>
<p>nice implementation. easy to understand. i plan to make it</p>
<p>Great instructable, did you take any measure concerning the mA you can draw from the small motor depicted in the photos at a reasonable cruising speed??</p><p>Thx</p>
<p>Keep in mind that hard drive motors are 3-phase - have fun with that. And the turntable motors in some microwaves have a high gear ratio where cranking it once a second will generate something like 400 volts.</p>
<p>This is a great device and has applications for other kinds of drive power. Like wind and water to power a bunch of LEDs at night or what ever one can think up. We need to come up with an easy regulater that has outlets for 3, 5, and 12 volts DC. That way you can power your LEDs, phone, tablet or whatever. The older RC car motors are cheap and they work great. The ones with ball bearing last a long time and can put out several amps.to charge batteries or caps. Thanks for the idea. It has been years since I experimented with the little motors as generators. Cheers</p>
<p>So it is strange to note 23.2V at speed then &quot;12V under load&quot; because the voltage generated should just be dependent on the speed the motor is running, not load. I don't think it should be effected by the load, that will simply determine the resistance of the generator wheel turning. This is assuming the generator wheel doesn't slip on the bicycle tire. Let me know if I'm missing something</p>
<p>I've made these in the past. Depending on the motor chosen to use as a generator, I agree using an automotive bulb is a good idea as they handle almost 14 volts. I would further suggest that a current limiting resistor as well as a zener diode (something in the 12v range) be wired into the system, just in case the cyclist really picks up speed and the generator exceeds the bulbs max. voltage.</p>
<p>when we were kids, they use to sell these in the stores and they lasted forever. Last forever??? There's no profit in that!!! Let's stop selling these and give them battery operated cheap junk. </p>
<p>The generator on that picture was a Chinese &quot;bottle generator&quot; I got for around 2 bucks. The wheel that comes in contact with the outer tire edge detached after some weeks of use, a testimony of superb building quality!!</p><p>I have, however, a 1950's model, maybe made on the US or Europe, it came from my grandparents bicycle. The surface finish and weight of the unit speak by themselves. If you want I can upload the pictures of it. </p>
<p>You can make a hand crank generator from a battery powered drill. Put an allen wrench in the chuck for a crank, and put alligator clip leads on the leads that go from the motor to the battery (remove the battery). The other end of the leads go to your light (or small motor). If you put a fan blade on these little motors you can make a tiny wind generator.</p>
<p>Hello qdogg! here's an excellent guide that uses your concept<br><br>https://www.youtube.com/watch?v=hCxmn1ERbXc</p>
Great minds think alike!
<p>Hahaha no doubt about it!</p>
<p>there are motors in hair dryers? Schwing!</p>
<p>That was the one!! on step 3</p>
<p>Well Done</p>
<p>Nice job, a next step could be to make it weatherproof!</p>
<p>Great little project. I am a Sr. Electronics Engineering Tech you explained this very well so that even a beginner or non-electrical person will understand somewhat of what's going on. Good Job!</p>
<p>Thank you by your comment PJSolarz, glad to read this, that was the idea I was aiming for!</p>
<p>Are you sure that the generator produces AC? Looking in through the vent holes (which you covered), it looks like a typical fixed-magnet, rotating armature with a commutator. This would produce &quot;DC&quot;, with a varying voltage, not the AC that is typical of the &quot;bottle&quot; generator (nice name, which was new to me with this article).</p><p>Thanks for such a detailed description. It takes time that most don't bother with.</p>
<p>Hello CarlM11!</p><p>Thank you for your positive input! You are correct, this specific motor does generate DC (that can also be confirmed on the picture showing the multimeter reading). However, after some friends accidentally ended generating AC (using brush-less motors) I prefer to tell the reader to always expect AC. Rectifying DC current will only waste power due diode drop, but may spare them the frustration of getting their (possibly expensive) LED fixtures burned. For the sake of technical accuracy I will include this on the guide, thank you again.</p>
<p>If you have Firefox you can send it to the pocket to review at your leisure.</p>
<p>Great write up! Passing this along to all my teaching friends. Fantastic primer. </p>
<p>Hey MichaelG9. What gets me about Instructables is that we give them all of this free information and they in turn want to charge us fee for this same information. I guess that capitalism at its best</p>
<p>It says you can download if you sign up, but then they want to to &quot;GO PRO&quot; and pay a subscription?</p><p>Just &quot;VIEW ALL STEPS&quot; and copy and paste!</p>
<p>Yes i needed to see that, thanks.</p>
I am definitely going to build this!!<br><br>Great job! :D
I am definitely going to build this!!<br><br>Great job! :D
<p>nice work</p>
nice one make sure you return the tire<br>

About This Instructable




Bio: My name is Felipe, I'm an Industrial Designer from Bogot&aacute;. I used to document all my works on my own blog, but today I ... More »
More by Menticol:Reviving a squeaky or jammed fan Pressure Wash with 100% Recycled Water Make a ultra-cheap generator for your bicycle (by cheap means from almost dirt!) 
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