mini wind powered generator

hello all. i would like to create a mini wind powered generator. i was hoping that i might be able to get some advice on designing a setup which will get as much current as possible.ideally i would like to be able to get enough power to charge a mobile phone. i dont want the span of the turbine blades themselves to be more than about 6 inches.i understand that it is possible to take an electronic motor and use that to generate electricity but is this a sensible solution for my problem? would a gear system be needed to get enough rpm to generate enough power? does this sound feasible? thanks in advance for any help.

you can use a bycycle dyanmo being in the construction of a small wind turbine, have a look at
http://www.reuk.co.uk/Dynamo-Hubs-For-Wind-Turbines.htm
http://www.youtube.com/watch?v=3ONp0qyFt0E
**broken link removed**

"As much current as possible" and "as small as possible" are
not compatible goals. A local optimum is the best you can
hope for, and that needs clearer goals.

A scrounged DC motor (like from a cordless drill) might be
a good approach, and the higher the battery voltage the
higher the motor-as-generator output. Without a gear (or
belt, or ...) reduction you will be hard pressed to get useful
voltage out of a small slow turbine. And a small radius turbine
would probably not have enough breakaway torque to spin
the drill head with its nice integrated gearbox, alas.

You might need to add a boost converter at the motor
output (low voltage capable) if you can't count on wind
speed and turbine details to get you the RPM to make 5V
(assume the phone is USB charged). You might also need
a 5V shunt regulator as a backstop in the event that you
do find "good wind".

I'd say to start with the turbine you can tolerate (size)
and put it onto any motor you can find, and measure the
open circuit voltage and short circuit current you can get.
This would be a sanity reading, to drive "next motor"
selection. You might also like an intermediate data point
like current@5V (the end game) to compare to the phone's
real charging draw, and some idea of what the phone's
response to undervoltage and overvoltage might be -
nondestructively obtained, you hope.

Have a look at a toy pinwheel. You hold it up in a breeze and it spins. It needs to be lightweight, and on a low-friction axis. Otherwise it will not spin.

It is easy to stop with your finger. That is the small amount of torque it generates.

Suppose you scale the size up to a large pinwheel. You might get it to spin freely in a breeze. You might get it to turn a motor.

i would like to be able to get enough power to charge a mobile phone.

Click to expand...

For a generator a good prospect is a cassette motor, or similar hobby motor, which will generate over 5V. You'll need to fabricate pulleys, gears, etc. The aim is to find a proper gear down (or up) ratio.

Unless you are in an area where the wind blows continuously at over 20 MPH, a 6" diam windmill will not deliver more then a few milliwatts. You will need a watchmakers lathe to construct the bearings to the required tolerances. A 9V motor from a cassette player is about right for your generator, a cycle dynamo is rated in watts and would not turn at all. The power output from a turbine is proportional to its diameter cubed, so doubling its size will give you eight times more power. Whatever size the turbine, it still needs to be high so its in a clear zone for the wind, so by the time you have built a 3m high tower, you might as well use a decent sized turbine on it.
Frank

it appears that i erroneously thought that a small turbine could generate more power than a small solar panel. i am surprised at how difficult it is to use one to get even a small amount of current! thanks for all the reply's.

A small solar panel is a good idea - I use one to keep the boat battery charged over winter

living in the uk where sun is a luxury i thought it might be wiser to use a small turbine since wind is so common.is it just very difficult to turn mechanical energy into electrical energy on a small scale?i watched a video of someone spinning a hefty axial flux generator with neodymium magnets at 2000 rpm and it only just managed to power up a lightbulb.i suppose in my naivety i thought electricity was easier to generate.no wonder we are so dependant on fossil fuels!