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Very powerfull joule thief torch flashlight

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.


  1. Haaa.. really good.. been interested in this joule thief thing recently.. impressed by the way, how much power can be juiced out of a dead cell..

  2. battery voltage should be above 0.5v , lower than that it doesn't work

  3. Hey buju 0.2 uF

    is this a capacitor.......becoz resistance has OHM as its unit
    and if this is the capacitor what is its voltage and whatz battery backup of ur torch

  4. you are right , its supposed to read "capacitor" not resistor.
    The torch uses a single AA battery.