Wednesday, September 29, 2010

Hand-cranked Torch Used To Power Radio

I've liberated the power from an inexpensive hand-cranked torch so it can be used to run an inexpensive FM radio. The torch contains a small rechargeable battery that is charged by turning a crank-handle.

Why? - This equipment is being sent to a part of the world where batteries are very expensive, where farmers need torches to manage night-time pests and where farmers need radios that give them access to weather reports which help with crop management.

Click Read More build details.

The model of torch was chosen because the plastic crank-handle can be easily replaced when it breaks, for its reasonably rugged build and for the three LEDs which give good light and last forever; And it was inexpensive.
I cracked open the case and found a series of gears connected the crank-handle to a small generator from which two wires connected to a small circuit board. The three LEDs are soldered to the circuit board from which two wires connect to an LIR2032 battery.
A quick search on google revealed that the battery was 3 volt / 40mAh - enough juice to power the radio.
Experimentation showed that the circuit board prevented too much power from reaching the battery or the LEDs and that when that little battery dies the hand-crank can still be used to power both of the devices.

Two new wires were soldered to the battery and their other ends to the two bolts to be used as terminals. A couple of holes were then drilled through the back of the torch case and the bolts pushed through before securing them with nuts. The whole thing was then put back together.

Next, I found a $2 FM scanning radio built to run on two AAA batteries. A quick look inside the battery compartment showed that the batteries were connected in series to provide 3 volts - just what I needed.
Two wires were then soldered to the battery terminals and a hole drilled into the back of the battery compartment cover. The two wires were then knotted to prevent them accidentally being pulled out before being pushed through the hole in the battery compartment cover and labelled.

The radio can now be powered by connecting the two wires hanging from its rear to the two bolts protruding from the back of the torch case, securing them with a second nut on each bolt.

I decided to keep the two devices as seperate units because the useful life-expectancy of the torch is much longer than that of the radio. The radio is also less expensive to replace.

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