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.
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.