school dc motor generator challenge

hello all,

we are working on a project for a high school engineering competition.
we need to generate electricity by harnessing the wind power from a floor box fan, then store that energy and use it to power a vehicle carrying a load (weight).

After some experimenting we have found that we can store a charge onto some capacitors and use that to power a small dc motor to run the vehicle.
Using 10F (2.3V) super caps we can run a little 3V motor for 5 minutes or so (we rigged two caps in series and two series sets in parallel) If we understand this right that should give us roughly 5+ volts with higher amps?
However the charging at this point has only come from a power supply.

Our question is this: What would be the best way to harness the wind power to charge the capacitors? (the charging and vehicle run must take place within 5 minutes.)

We have tried using 12V computer fans/motors. With the floor fan set on high, we can at best get 2V from one comp fan. We tried rigging two series sets of 3 minifans in parallel to get close to 6V at unknown amps. This takes forever to charge the 10F capacitors....

Are the 12V motors a bad choice, if we can only spin them fast enough to generate 2V? Would it be better to run say a little 3V motor to generate the 2V?

We need some help to figure out this last hurdle...
Thanks a million!

Hi Verdonko,

if the project is not fixed to DC-motors you might try small stepper motors, e.g. a stepper motor of a print head. They generate pretty good voltage even at low rpm.

A bipolar stepper motor has two windings which you might connect to a bridge rectifier each and parallel the rectifier outputs for higher current. To reduce ripple use electrolytic caps for smoothing.

I haven't measured the output current yet, but depending on the input power (e.g. the motor rated 5V, 200mA) you should get about 150mA out.

Boncuk

verdonko said:

Using 10F (2.3V) super caps we can run a little 3V motor for 5 minutes or so (we rigged two caps in series and two series sets in parallel) If we understand this right that should give us roughly 5+ volts with higher amps?

Click to expand...

Wiring up four 10F/2.3V supercaps as indicated above gives you 10F at 4.6V. (The first two in series gives you 5F/4.6V, i.e half the capacitance but twice the voltage rating. Wiring two such sets in parallel restores your capacitance back to 10F, and maintains the new voltage rating.)