Together a friend and i built this hand powered light, the idea just came to me while we were playing around with some stepper motors i had salvaged over the years from various things like printers and scanners.
My Hand Powered Flashlight
Sorry for this terrible schematic, i download a really junk program to make this one, if you know of a better one please let me know.
Here is a brief explanation of how the circuit works:
1) the stepper motor is spun, generating AC power.
2) AC from the stepper motor is rectified by the 2 full wave rectifiers into DC.
3) DC power from the rectifiers is then stored in the 12,000 uf 50 volt electrolytic capacitor.
4) voltage from the capacitor is regulated by a 7806 6volt regulator.
5) current draw (amps) of the LEDs is regulated by the 300ohm resistor.
6) the 3 LEDs which are connected in parallel all light up, a better way to do this would be to use a seperate resisor for each led.
The reason for the voltage regulator is so that no matter what voltage is in
the capacitor you will stil have a constant current
and voltage going through the leds even if say the capacitor had 50 volts stored or only 10, although the voltage regulator
does have its drawbacks, for instance the higher the input voltage the more energy is turned to heat when it is lowered to 6 volt.
because of this the metal tab on the back of the 7806 does get warm to the touch, although not warm enough to warrent a heat sink.
The whole circuit would be much more efecient if it used a higher farad capacitor that wouldnt get so high voltage, maby i could regulate
the voltage going into one of thoes 1F 5.5 volt memory caps or something like that to make it last longer.
the result is a hand powered light that when cranked for 10 seconds will shine for 30 seconds.