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
http://www.altronics.com.au/index.asp?area=item&id=R4945

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,
http://www.reuk.co.uk/Using-The-LM317T-To-Regulate-Voltage.htm

-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
http://www.jaycar.co.nz/productView.asp?ID=ZD0424&CATID=33&form=CAT&SUBCATID=917

-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.

Comments

[sumaru]

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

[gordoflash]

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.

[tinstructable]

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.

[gordoflash]

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
http://www.tpub.com/neets/book2/3e.htm

[Wisley]

that there would be a 100mm PVC pipe?

[gordoflash]

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

[loccci]

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

[gordoflash]

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!!

[loccci]

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

[gordoflash]

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.

[hobbyhawk32]

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?

[gordoflash]

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.

[hobbyhawk32]

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

[jules15]

or just use a regular 2 wire motor

[gordoflash]

Yes you can.
But a 2 wire motor requires alot more rpm to produce the same voltage and will struggle to produce the same amps.
A stepper motor only requires 200rpm so fitting it to the hub instead of the rim will make less work for the cyclist.
That was the whole reason for the instructable.

thanks for your input