My Joule Thief


Introduction: My Joule Thief

A Joule thief: (1) is a device that will suck and all of the juice from your "dead" batteries (2) To make it possible for an LED with a voltage requirement of higher than 1.5 volts to run off of a single 1.5 volt battery! For example, run a white LED from a single AA battery! or im my case run 2, 4volt Leds off a battery measuring 1.2 volts on a voltmeter!!!!
I made using 1ups instructable. I just added a switch and put the project in an old Chocolate tin (Altoids tin).

if your wondering what the coil is/ what it dose. Its a hand wound Toroid. I got 15 Toroid Beads out of my old dead x box.
This circuit works by switching current back and forth 40hrtz (40,000 time per second) the Coil builds up a charge from the >1.5volt battery once it build to 4-8 volts it switches the power to the Leds, they light up and then the current is switched back to the Coil and the Cycle repeats faster than you eye can see.
great use: writing with light



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    29 Discussions

    Here's a Joule Thief with 10 LEDs on a 9v battery:


    Awesome job! I still have no idea why they're called Joule Thiefs, but awesome job. All of 1ups Instructables rule! And this one is cool too. Where did you get the circle thing? I forgot what it was called.

    11 replies

    its a hand wound toroid. i took apart my old (already dead) xbox and found 15 Toroid Beads. you just wrap 2 wires around the bead 8-20 times. and its call a Joule thief cause a Joule is a measurement of energy. so your trying to suck all the juice out of the battery. Basically why throw a battery away when you can put in in a Diy flash light. (more info now in the description)

    Why a blue and a white LED? Any special reason? What would the difference be between an 8 turn toroid vs. a 20 turn toroid? Would it have a capacit(atoring?)(ending?)(orizing?) effect? So would more windings smooth out the pulse like a cap? My understanding of the way the oscillating works is...50%. (crud. 15 toroid cores - that's more than I've gathered in the last 2 years...boohoo)

    They are really called simple Hartley Oscillators. It's a pun of "jewel thief" and Joule units.

    if i were to put alot of dead betteries on this could i use it to power something else?

    NO! It could fry complex circuits,and would be useless because it pulses the electricity.

    BTW a joule is how much energy is needed to push a object with a resistance of 1 newton (100grams) 1 metre.

    joule - that-s the measuring unit for any kind of energy, thermal, electrical or otherwise. a joule thief is a THIEF that steals the last bits of energy from nearly-dead batteries, that have a very low voltage, and cannot power devices which require a voltage above a certain treshold value, like led's do.

    The self inductance of a coil is directly proportional to the square of the number of turns on the coil N .The inductive reactance of a coil is equal to XL= 2(pi)f(L) . We then have the current in the coil is equal to : I = v/(XL) = v/(2(pi)f(L)). I am not sure about how the frequency of the circuit will vary with N ; but , I will say that increasing the number of turns will eventually limit the output current because the inductive reactance wil become so large . I am making the assumption that the frequency stays large as we increase N .