Instructables
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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.
HOW IT WORKS
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
colin552 years ago
Here's a Joule Thief with 10 LEDs on a 9v battery:
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nice, just t note, I've read the switching speed is closer to 40KHz then 40Hz
thats 40,000 times a second?!
Yep
40 Hz you could HEAR!!! It would sound like a fat guy humming...
Kirbsome!4 years ago
Does more turns equal higher efficiency?
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I think that toroid looks scary...but it might lower efficiency. Don't waste turns.
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.
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)
Wow...you hit the JACKPOT!!!
i make shooting things (author)  Udon5 years ago
nope they we just rolling around in my desk drawer
They are really called simple Hartley Oscillators. It's a pun of "jewel thief" and Joule units.
junits15 VIRON5 years ago
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.
a cap should even it out...
BTW a joule is how much energy is needed to push a object with a resistance of 1 newton (100grams) 1 metre.
Its a pun off of JEWEL THIEF. It "steals" joules (measurement of power) from dead batteries.
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.
pk27122 years ago
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 .
 This joule thief thing look much like the circuitry used on camera flash bulbs. Using more wire turns and a capacitor instead of a battery may enable you to light a flash bulb. But for flash I think it would be better if you use more batteries in series (3 or 4.5v) and non-dead batteries.
animaster5 years ago
does a 2n2222 work?
-Aj-5 years ago
just a quick one, 40 Hz is 40 times a second. 40,000 would be 40 kilohertz or 40khz this 'joule thief' thing is similar to the dc/dc power supply in single battery led torches that have a 1w superbright led or similar in them
theburn76 years ago
how did u do the light drawings
Camera on tripod in pitch black room. Set camera to long/manual exposure. click shutter button. using a light with on/off step back 6-10 feet shine light/draw what you want and click the button again to close the shutter (if its not manual it will do it for you obviously) for instructions that make since check out this instructable
mikedoth6 years ago
Can someone explain what the coil's maximum (theoretical) limit it will reach with a single battery? I can expect that it depends on how many windings you have but i'm sure it can only go so high, right?
i cant help you out there. ask unknownuser2007 or 1up (there instructables should to the right and bottom of this page)
westfw6 years ago
Ah. Nice; a fine use of a slideshow; showing your own implementation of an existing instructable!
i make shooting things (author)  westfw6 years ago
Thank you.