A crank flashlight is wonderful to have on hand; you never have to worry about the batteries. I have one that I use all the time. I decided to take it apart to see exactly how is functions, and there’s really quite a few things in there. The flashlight has one big button plus a crank you turn to charge it up. If you click the button once, all three LEDs light up, if you click it again just the center one lights up, and clicking it a third time shuts it off.
I started by remove four screws on the back to reveal the inside.
Inside, there’s a DC motor that connects to the crank shaft. When the crank is turned, the DC motor turns too, which generates a voltage, and the battery charges up. The push button, which is right in the middle of the PCB (printed circuit board), which is the only input to the system. All of the capacitors, resistors, and diodes are used to control the process through which the LEDs cycle through the on and off cycle. I was interested in the four-legged integrated circuit (IC) in the middle. I’m used to seeing eight-legged ICs.
Next I removed the screws (circled in yellow in the above pic) holding the PCB to the black box. From there I could remove the clear plastic shell around the light, and pull the PCB away to reveal more screws that attached the whole chunk to the outside shell. There’s only three little LEDs that provide all the light given off by the flashlight!
Finally, I took apart the black box which contain the gear mechanism for the crank. The three gears are set up so that turning the top gear (connected to the crank shaft) slightly makes the bottom gear (connected to the motor) turn a lot. You can see there’s some slimely stuff that looks like petroleum jelly all over the gears to help the turn smoothly and quietly.
After I took it all apart, I put it back together using only my trusty little phillips screwdriver.