Bike Light Generator




This project came about because batteries go flat. Especially when you don't want them to.

If you want a bright light on the front of your bike and don't want the hassle of recharging batteries or heaven forbid having to buy new ones, then check this out.

Some expense is required, but no more than the cost of a decent halogen head light.

Also there is some manufacturing involved, but if your still keen, this system works.

The specs are
-No Batteries!! Energy Storage is two supercapacitors 100F, 2.7volt in series, giving 50F at 5.4volts.

-It takes a few minutes to charge but the light will work at full brightness as soon as you start pedaling.

-It has a 15min run time before it starts to dim (when you stop at the lights and the generator is not running) .
The 1Watt LED requires 3.5volts, using the right resistors this time can vary between 4 to 30 mins.
The LED can draw up to 350mA, but my setup drew 160mA, still bright enough to dazzle drivers.

-The generator can run the light and maintain the charge. I used a Stepper Motor from an old dotmatrix printer, it can generate 500mA when shorted on a multimeter.

-Another advantage is the capacitors have no memory problems and are self regulating (meaning they cannot be over charged).

Step 1: Parts Required

First you need to source a decent Stepper Motor. You need one with a very low resistance in the coils, this should give you the Amps required.
Mine had 2.88volts and 2.4A on the label, the resistance was 1.2ohms across the coils. On testing this Stepper motor put out 500mA when shorted with the multimeter at 400rpm!!.
At 15km/h the average bike wheel will be doing around 160 to 200 rpm. That means the motor could be mounted near the hub of the wheel reducing the effort to drive it, unlike the old dynamo running on the tyre at a 1000rpm.

Secondly, you need to purchase a couple supercapacitors which could be found here

Thirdly, you'll need

-x8 1N4004 diodes,
these will rectify the AC generated by the stepper motor to a DC supply.

-x1 LM317T Voltage Regulator,

-x1 0.1uf ceramic capacitor (suggested by LM317 datasheet)

-x2 Resistors for the LM317T, a 240 ohm and a 820ohm 1/4watt will give you the 5.5 volts needed for the capacitors, this should not be exceeded!!

-x1 LED 1 Watt

-x1 Resistor for the LED, 11ohms 1/2watt, this creates a current draw of about 160mA.

Other items to find are
a torch/headlight case to fit the LED into.
a small case to protect the capacitors from damage.
Some wires.
A 100mm dia. plastic drain pipe approximately 25mm wide, epoxied to the spokes of the wheel.
A pulley or rubber wheel for the stepper (approx 50mm dia) and
tools, soldering iron, and what ever is required to fit it to your bike.

Step 2: Building the Generator Circuit

Firstly I didn't use a circuit board, I just soldered the components together and then covered with an epoxy glue to protect it.
My Stepper Motor had 6 wires, 2 are Com which you don't use, and the other 4 come from the coils.

Solder the diodes together like the diagram, this creates a parallel circuit giving you a DC supply.
Solder the Capacitor between the + and -, this stabilises the Voltage Regulator.
Then solder the LM317T and the resistors in place.
Fit the LED into an old headlamp with the current limiting resistor.
Run the wires from the light to the Capacitors via a switch, and then down to the voltage regulator.

Stepper Motor==Voltage Regulator==Capacitors==Switch==LED

A slight modification I did was to add a resistor in series to the Capacitors to limit the charging capacity. The reason being if the capacitors are flat they will pull the voltage to low for the LED to operate. The down side is the Capacitors will take longer to charge but the LED will work straight away.

To Be Finished with more photos to come.

Step 3: Fitting Stepper Motor to Bike

Finally got around to fitting the stepper motor to the bike.
I used Metal Pipe clamps to hold the motor and used the mounting holes normaly used for the disk brakes.
Used an old bike tube as a tensioner, ( not shown in photo)
The Motor wheel is running on a section of 100mm dia PVC pipe, This was fixed with glue and tape, but might need screwed clamps as the Bike tubes tension needed to be good to stop wheel from slipping.



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    22 Discussions


    4 months ago

    Would you be able to post a complete electrical schematic? Thanks!


    2 years ago

    I have sourced a stepper motor but the calculated resistance is roughly 68 ohms with load. I'm very new to this thing, but my guess is that the resistance is way to high, correct?

    Here's the specs for the motor:

    2 replies

    Reply 2 years ago

    I believe the motor you have is not a stepper motor, stepper motors have 4,5 or 6 wires, not 2. The DC motor will produce power, but not enough. The stepper motor I used will generate about 1 amp I think.


    Reply 2 years ago

    Ah, drats. I had hooked it up to a cheap dollar store circuit board with two LEDs. I spinned the axel with my finger and got near-full light. The motor was from a stereo system I took apart...I'm not sure what it was used for, but my guess is that it powered a mechanism that spun the interface open when the stereo was given power. I figured the bike would power more current than just my finger. I might try to experiment around with it until I find a more appropriate motor, but thanks for the confirmation!


    3 years ago

    Nice instructable! One day or the other I want to put together a bicycle charger for my phone, requiring 0.5 to 1 Amp to charge in a decent time. Anyone knows how to guess, from the several stepper available, how to choose the one sufficient to provide a current in that range?


    5 years ago on Introduction

    hello guys;

    i have sun tracker project, i wanted anyone can help me to know the specifications of my supercapacitor ( my dcsource voltage is 20 volt and i want 1 amp current for my actuators)



    8 years ago on Introduction

    Nice, will all kinds of motor work? how about motors with no permanent magnets, will they work?

    1 reply

    Reply 8 years ago on Introduction

    it would depend on the motor, try spinning it with a battery drill and have a multimeter or small torch bulb attached and see if you get anything from it.


    You say that two 100F capacitors at 2.7 volts wired in series is equal to 50F at 5.4 volts... that is incorrect. You still would have 100F. Two wired in parallel would give you 200F at 2.7 volts, and in series you stay the same Farad rating.

    1 reply

    sorry, I google stuff like that as I'm not an electrical engineer.
    I discovered the equation for 2 capacitors in series is,

    Ct = C1 x C2 / C1 + C2

    more than 2 capacitors, it should be

    Ct =1 / ((1 / C1) + (1 / C2) + ...(1 / Cn))

    taken from


    Reply 8 years ago on Step 3

    that there would be, about 25mm of it. I cut slots with a hacksaw to hold it on the spokes.


    8 years ago on Step 1

    hi, how do you mount the stepper motor? where does it touch on the bike?

    1 reply

    Reply 8 years ago on Step 1

    I only just got round to it my self. I will update with pics on that asap. I used a section of 4" pvc pipe epoxied to the rear spokes to run the stepper on. I held the stepper to the bike using metal pipe clamps. will try to update before the weekend. My wife thinks its great and wants the back lights running off it as well!!


    8 years ago on Step 2

    i dont understand how to use the capacitors, where do i put them? Im finding it difficult to find any information on how to use capacitors with a stepper motor to store charge while also using leds. thanks

    1 reply

    Reply 8 years ago on Step 2

    you fit the capacitors the same way you would batteries. the difference is in the way they charge and discharge also, the voltage sent to them must not exceed the capacitor voltage value, hence the voltage regulator. I will try to update the instructable with another more complete circuit.


    9 years ago on Step 2

    How do you tell which wires are com and which are from the coils?
    How can I be sure that my motor will work for this?

    2 replies

    Reply 9 years ago on Step 2

    How many wires come out of your motor? 4,6 or 8
    4 wire motors have no Com wires, which can make it easy.
    6 and 8 wire motors, you should still only end up with 4 Coil wires.

    Use a muiltimeter to find the resistance (ohm) value between wires.

    Coil to Com value should be approx. half the Coil to Coil value.

    4, 6 or 8 wire motors can all be used,  join all com wires together.

    any problems, let me know.


    Reply 9 years ago on Step 2

    I have a bunch of motors, most have 8, I think 1 has 6, but some have 12.
    thanks though, this really helps.