LEd survival

[Voltboy]

Hello.
I was the other day in a store and I saw a LED survival flashlight that it got power by shaking it.
**broken link removed**
It looked like that one, just that it had two coils instead of one.
I saw the PCB inside the LED and I could see 8 diodes, a capacitor (I will talk about it later), a red LED and a white LED, and 2 resistors.
I guess the diodes are for rectifying (if I'm not wrong the magnets with the coils produce AC current), but you only need 4 diodes for a full wave rectify, why it had 8?
Each time the magnets went trough the coil the red LED flashed, that easy thing.
But now, the capacitor, I stay looking at it alot of time, I couldn't see any values because the color was diffused, and after a time I star suspecting its not a capacitor. It was kinda axial shape, but it had like a slope in the middle which made me thought it was an inductor, but I don't know.
So if anyone know anything about it I'll appreciate alot

Thanks

 

[Nigel Goodwin]

You might try searching the forums?, there's been a lot about them over the years - basically a magnet is moved through coils and used to charge a capacitor - basic electrics!.

 

[Oznog]

Actually the one "crank" type I took apart did NOT use a capacitor but a rechargeable lithium battery in one of the standard "button battery" forms, like CR2320 or something.
I looked it up, the batt type is relatively low capacity, something like 1/10th what a primary non-rechargeable lithium batt in the same case size would have.

 

[Nigel Goodwin]

Actually the one "crank" type I took apart did NOT use a capacitor but a rechargeable lithium battery in one of the standard "button battery" forms, like CR2320 or something.

The hand cranked ones do (I bought one the other week), the shaking ones usually use a capacitor instead though.

 

[Hero999]

I have a cranked LED torch, it says it has a lithium battery in it but when I opened it up it had a NiMH battery in it, consisting of three button cells. The battery doesn't last for that long, after cranking the voltage measures 3.6V but iot quickly decays to 3V after a few seconds and the LEDs aren't very bright.