I decided that I wanted to try and build the most powerful single cell torch using the joule thief circuit. The toroid that I used was not a ferrite ring but rather a steel ring with as many windings that I could put on it using very thin wire. In this configuration its powering 4 x 20k mcd LED's with hardly any loss of brightness. I also experimented with the resistor and found that a 0.2 ohm worked the best. The housing came from a old "maglite" type torch.
this is where I got the idea: http://www.instructables.com/id/Make-a-Joule-Thief/?newComment=true#comments
I used this schematic , but used a BC337 transistor and 0.2 ohm resistor.
First I made a test rig as usual:
Then I compacted all the parts to fit into the torch:
Put it all together and tested:
For some reason it would not work with 2 AA batteries in series , perhaps it was the toroid.
So the final product, with shortened body looks like this:
|powerful joule thief torch|
|powerful joule thief flashlight|
I'm quite impressed , small , compact and bright enough to light up a room.
Other AA flashlights you can purchase.