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How Battery-free Flashlights Works.
It sound too good to be true. Let's see how these battery-free flashlights works. (5/20/2006)
Source: http://www.josepino.com/?how_flashlight Tags: light
circuits
electronics
I decided to build my own "Battery-free" flashlight after I saw it on TV. After a while, I came with the idea how it works and I created this schematic:
Taken from http://www.josepino.com
I decided to use germanium diodes because the forward voltage is only 0.2 Volts and it will not discharge the capacitor faster as silicon diodes do. The silicon diodes have a forward voltage of 0.7 Volts.
I was not able to build my own battery-free flashlight because the frame and the case are not easy to build. I forgot the idea for long time until my honey bun gave me a battery-free flashlight as gift. Here is the picture of the flashlight that I got:
Before I said "thank you", I disassembled the flashlight. Here is the flashlight in parts:
As you can see, there is some interesting parts:
B Plastic Lens
C Rubber (stops the magnet when it is shaked)
D Magnet imitation
E Two Lithium Batteries.
F Circuit board with only a white LED.
I Copper coil connected nowhere.
YES! this "battery-free" is a fraud! This imitation can be purchased with only $1 USD or little more, but look closer this detailed picture:
As you can see, there is not circuits, the coil wires are soldered at one point, so is not functional. This "battery-free" flashlight works with two CR2032 Lithium batteries.
I tried to call the company that manufactures this flashlight, but the box doesn't have any information. How this product came to the USA without the legal information? I have no idea and I don't want to talk abou it.
I went to buy the "real" battery-free flashlight to see how it really works. Here is the picture:
As soon I started to disassemble this flashlight, I found the magnet is really powerful. My tools immediately stick to the magnet.
I found that this flashlight have an interesting design. It doesn't have any resistor neiter a switch. Instead a switch it have a reed switch. The diodes used are silicon diodes and the capacitor, as I thought, is 1F 5.5V.
The reason why there is a reed switch instead a regular switch is because this flashlight is water proof.
This product is not too bad. To be honest, I prefer to use flashlights with batteries unless it is really needed for an emergency. Is not worth of shaking it for 40 seconds to get about one minute and half of light.
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08/09/09 - 17:48:26 acmefixer from near Disneyland wrote: I bought a shake light and was very disappointed in its performance. You shake it a long time, and the light immediately gets dim after you stop, and is weak for only a minute or two. Later I bought a crank light, and it performed much better, I looked inside and found that it uses a rechargeable lithium cell instead of a super cap. My advice - never buy a shake light.
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