Contactless Dynamo Bike Wheel Lights




On this instructable you will see how to power some LEDs spinning in a bike wheel without any battery. This project is very similar to another one previously presented ( ), with the difference that now the coils and the LEDs are spinning and the magnet holds still.

What you will need:
  - 3 relay coils (I had some with 200 and others with 600 windings);
  - 1 HD magnet;
  - 3 diodes (general purpose diodes are ok, I used 1n5818 schottky for the low voltage drop);
  - 18 blue LEDs (you may use how many you want or even other colors - white is also cool).

For the continuous mode just add:
  - 1 capacitor (4700uF seemed fine, you could test some other values);
  - 1 switch to be able to choose between modes.

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Step 1: Circuit Diagram

Each coil is placed in series with a diode and three of these configurations in parallel. This way when one coil is providing energy, that power will not be consumed by the two other coils (simple half wave rectifier). The current flows directly to the LEDs where the voltage is the one generated by the coil with about 0.6V drop at the diode in case of a general purpose one. For a schottky it should drop only 0.3V or even less.

When the capacitor is connected to the circuit, it will be charged and will keep the LEDs on for some time when no coil is providing power.

Step 2: Rear Wheel Setup

I used pieces of aluminum to place the coils on the spokes. There is a gap of about 4mm between them and the HD magnet.

LEDs have their anodes wired to the circuit while cathodes are attached to the spokes, which are connected to the coils. This makes less wires around the wheel.

Step 3: Front Wheel

Here we the setup from the older instructable applied to the front wheel. The circuit is just all LEDs (1 blue + 5 white) in parallel with the one coil. The blue LED is located ate the coil and the white LEDs are on the front light.

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    29 Discussions


    Reply 3 years ago

    Doubtful, since it's going to be air cooled - the faster you go, the more it gets cooled. As for overloading, if in doubt you could always place a limiting resister or regulator, but those coils aren't really going to be too much of a risk


    5 years ago on Introduction

    Has anyone seen any instructions with getting something like this to work with revolights?


    6 years ago on Introduction

    Just did this on my girlfriend's bike. She's so happy. Great instructable!!


    7 years ago on Introduction

    Would you get the same effect on continuous if you used 5 high brightness leds instead of 18 standard leds?


    7 years ago on Introduction

    Hey what LED's did you use? I'm trying to figure out the maximum forward voltage so they aren't blown


    8 years ago on Introduction

    I'm just wondering if changing the diodes into a bridge rectifier setup would help - at the moment to my thinking you're losing half the energy generated. Looks great, though. I'm seriously tempted to build one of these for my bike wheels. Just have to scrounge the parts.
    At the moment I'm using battery powered blue wheel lights - big chunks of silicon that slide in between the spokes.

    1 reply

    8 years ago on Introduction

    im looking at putting thison a sport bike but could you put another video up? youtube wont let me see it


    8 years ago on Introduction

    Ooh i totally love bicycles, theres so many things i want to add to it =P You got real good project. Thanks for giving inspiration to me.


    8 years ago on Introduction

    hey friend, i failed to find a relay coil so i used a small 12v transformer. with normal magnets it produced around 6 mA. hhah is it because of the magnets or coil length
    as i recon resistivity is propotional to length,area of crosssection


    9 years ago on Introduction

    by the way, nce song - viva la mano negra ;-) !


    9 years ago on Step 3

    wow this is great, I commue by bike everyday and I'm looking for a solution to be seen this winter. last winter i had blinking lights hanging from the bike, my bag and so on but this year i'd like to have it on the bike.

    the other i saw the led blinking bicycle tyre ( which look amazing. Now I found your instructables which +/- does the same; unfortunately it looks a bit beyond my knowledge :( I have no eletronic knowledge at all


    9 years ago on Introduction

    Is it possible to use ordinary magnets in place of the HD magnets? I have some strong magnets I might be able to use if so.


    9 years ago on Step 3

    I don't know if HD magnets are proper, because they are half N and half S.And not on the opposite site (that's normal), but on the same side. To prove it, put 2 different magnet on contact. Too difficult to explain here, just think on what you expect by normal magnet and verify that it does _not_ happens. You can cut it in half, but i read that high temperatures generated by the cut may demagnetize them (if you use grinding machine). The efficiency is very low here i think. But you spent nothing for neodimium magnets, so i approve your choice and your project! :) Anyway is better to know this characteristic of HD magnets. Bye.

    1 reply

    Reply 9 years ago on Introduction

    perhaps i'm mistaken, but i think that cutting the magnet would just make two magnets similar to the original (provided they weren't demagnetized. Again, i'm not really sure.