how about crank lights?

I got a wind-up/crank light for xmas, the one from costco with 3 LEDs. It is pretty bright when wound up, and I leave it in the car to use if I can't find another light. It doesn't have a battery in it, just a metal plate that stores the energy somehow. Overall it is a pretty good product... but not something I would use for any specialized task.

One nice thing about this light for keeping in the auto is that it doesn't need batteries which are sensitive to extreme temperature changes. I feel comfortable knowing that it WILL light up when needed. Probably wouldn't have bought one for myself, and considered re-gifting it, but decided that the glove box would be a good place for it.

How does it work?

the crank is attatched to a large gear through a shaft into the body, the large gear turns a much smaller gear to increase the RPMs.. some crank lights may have multiple gears to increase the ratio farther. (so that 1 turn of the crank, will result in many turns of the final shaft).. I would venture to guess the ratio is somewhere around 1:10 or higher...

The final shaft, probably turns a set of small magnets(2, or 4, or more, even numbered) The magnets are mounted to the shaft such that apposing magnets are facing with opposite poles outwards. mounted just next to the magnets that are turning, there is probably 1 (or more) tightly wound coils of magnet winding wire (probably 30ga or smaller)... If there are multiple coils, then they are probably wired in series to increase voltage.

I have just described a perminant magnet generator design. The output is AC power. The frequency of the AC is dependant on RPMs, and has to be rectified to be used in a DC device. A small rectifier is used there. Then there is probably some form of electrical storage device, in this case, probably a capacitor.

not sure if this answers your question... and to be honest, i'm not 100% sure this is the method used by the light.

here's the daddy of crank lights. Freeplay has an internal spring that you wind up for a long runtime. has a regulation balance wheel simular to a clock.

I too got a crank light for christmas from my uncle and ue it alot in my truck. My uncle knew I was a flashaholic and was impressed with a bunch of flashlights l took with me to a family gathering that lasted well into the early morning at my other uncles farm with no other lights like those found in a city. I think i'm winning him over to the "light "side but the prices that l paid for a few of them kinda keeping him from converting.