Make a Joule Thief

Yes, it's the infamous Joule Thief, in Instructable form! For those of you who don't know, the Joule Thief is a tiny little circuit that allows you to drive a white or blue LED from voltages as low as 0.5 volts. You think those batteries are dead? Don't throw them out yet! Hook them up to the Joule Thief to squeeze every last drop of energy out of them!

The idea and circuit came from this Make weekend project. Why don't you pay them a visit?

Step 1 Parts and Tools

For this project you will need very few tools and parts, as you will see in the picture below.
But for those of you who like it in text, here it is:

Helping Hands (Optional)
Soldering Iron
Solder
A Blue or White LED (Other colors are fine, too)
2N3904 Transistor or equivalent
1k Resistor (Brown-Black-Red)
Toroid Bead
Thin wire, two colors (magnet wire works)

You can get the toroid and transistor from a dead CFL; the transistor is usually labeled 13002.

Also, if you use a 2N4401 or BC337 transistor, your LED will be brighter because they can handle more amps.

Comments

[Malkaris]

I've been playing with this for a little bit and I've had 0 luck getting the LED to light with the setup explained. However, I put a 1uF cap across the 1k resistor and it worked.

I can't figure out what is could be different in my setup that requires the cap.

Any thoughts?

[nodoubtman]

Why should i use a transistor ?

[WildWalkerCT]

because the transistor will drive the toroid transformer by switchingon and off at 50 KHz

[sconner1]

Looking for a torroid?
Take apart a burned out spiral lightbulb.

[claymantoo]

Thanx 1UP!!!
I couldn't get it to work though until I removed the resistor.
Works fine without one.
It works with the said resistor if I put it at the beginning of the circuit, but of course the led is dimmer.
Nothing I tried otherwise worked.

What is the reason for the resistor?

I'm sure that Question has been answered before but I don't care enough look through 641 posts to find out.

Anyone want to take a sec to answer this?

I'm using a ferric torrid,
magnet wire,
<1.5v AA Batt.,
2n3904 transistor,
NO resistor???

[sconner1]

The resistor is to protect the base of the transistor from voltage spikes above the maximum rating preventing damage to the transistor.
It is Not supposed to be in series with the led like the usual job of current limiting.
With only 1 battery, going without the resistor (I hear) should work fine.

[ssuman1]

Hello will joule thief be able to light up n LED from salt watr

[dill1104]

I have tried 7 different times to build this, and I am getting nothing.  I started with #22 wire but could only get 6 wraps on my toroid (radioshack 10 pack)  I then moved up to using #26 and #30 gauge wire..still with no results.  I was using a 1.1k resistor (gold,red,brown,brown) and then switched to a 1.0k (gold,red,black,brown)  My transistor is the same as in this post.

Does the LED matter?  my toroid is about the size of a dime...is that big enough?  What size wire is best...is enamel okay to use?  Does it have to be a WHITE or BLUE LED?  I am also testing with a new AA battery

any help would be great! 

[1up]

I've gotten this from a LOT of people.

And I really can't figure it out, at all. :/

People always tell me they did everything right and it still doesn't work.
Assuming you have checked for shorts, etc, have you tried a different transistor? Maybe you burned it out.
You know the two wires coming out the other side of the toroid? You could try switching them.
After that, I'm not sure what to do. Maybe it's a thing with the toroid? Tell me if it's magnetic or not.

[yaja]

For me, scraptopower's idea of switching one of the windings around worked. Disconnect from res and and batt and reverse. Don't unwind. Thanks

[ifarhan1]

can we use this to charge mobile phone batteries? If can, how?

[1up]

No, it doesn't put out enough current. Plus, it's really constantly switching on and off, not providing steady power.

[ifarhan1]

what is the amount of current needed to charge mobile phone battery? can i use the transistor to increase the current? my idea is to connect the joul thief to my created earth battery. Can i?

[Winu]

i'm also interested of doing something similar... right now im trying to do a decent toroid and finding the right resistance for such application. I think that if you can add a capacitor to temporarily store the charge, it might help somehow.

However, to the circuit you might want to add a voltage regulator (say, an LM317 found in UPS systems) and with the use of resistors you can set a steady current at a specific EMF. For the voltage regulator setup to work you need a voltage input which is greater than your desired output so you probably have to tune your joule thief. The addition of a secondary coil to the toroid (to step-up the voltage) can be an answer.

I'm just a hobbyist with just an intermediate level physics. :P Research just got me better. xd

[Ray Power]

Thanks for the instructable! I could only get 4 wraps on my CFL salvaged toroide but it seems to work

[nodoubtman]

What is the role of Toroid here ?

thanks!

[ernie666]

I tried to make this circuit so many times with no LED lighting up. I figured that maybe the 1k ohm resistor had too much resistance, so I swapped it out with a 560 ohm resistor and surprisingly, it lit up.

[Yewfort]

Does it matter what the toroid is made of ?

[emcelhannon]

Can I prolong the life of 2 double A batteries that power a 3v motor?

[Vick Jr]

Does anyone know where the "8-11 turns" of wire comes from? Is this from trial and error or Is there an actual equation where you plug in the I/O voltages, current, frequency, inductance, etc. and solve for the number of coils? (I like physics and ideal models.) : ] Knowing a formula like this could also help people optimize for using different power sources, LEDs, transistors, and torroids.

[poza]

your question is a year old, to be sure, but i'm working on a somewhat similar electronics project and i stumbled across your question while looking for answers to my questions. i have no knowledge on this subject and i'm in the process of learning as i go. i found a formula that mentions the number of turns around a toroid. you might check this out: http://www.mantaro.com/resources/impedance_calculator.htm#toroid_inductance

[robot1398]

can i use a bc547 transistor in place of 2n3904

[-max-]

i used a transistor out of a flash camera, it worked. after playing a lot with it, i found the 2n3904 to be vastly superior. most other transistor didn't work or barely did.

[robot1398]

i made it with bc547 and works better than 2n3904

[-max-]

great for you! i dont know if half the transistors i used were NPN or PNP. i think most were PNP

[robot1398]

then how did u know the pinouts

[robot797]

all npn transistors work

when i build one
i get my junk box and desolder the firsth npn i see :P

also if you make the 1K resistor a 2 or 5 K pot you can tune it into the right frequentie

[robot1398]

thanks

[RONEDOGG]

i just tried this for a xbox 360 controller leds. and well it didnt go so well. i used the same size troid same transistor but my resistor was abit different. it was grey in color. and it heats up liek bad. enough where i have a blister on my leg where it fell. lol

any idea what transisotr to use for 4 LEDs?

[S33PlusPlus]

Sounds like you either shorted the supply rail to ground or overloaded something (the transistor can only dissipate 100mW or so, and the most abundant resistors are rated for 1/4W)

Which parts got hot? And is there a reason you need to drive the LEDs with a joule theif?

[RONEDOGG]

hello. you might be right. i did short out the transistor it started making a high pitch noise after.
it was the resistor that got hot. but i realized that after i forgot the battery on the xbox controller is 2x 1.5v.
i started over again and got it all working.

the reason for the joule thief is with wireless xbox 360 LED ABXY mods, when the battery gets under fully charged the LEDs in the controller dim really fast. and its noticeable after about 30 40 mins of using the controller on a fresh charge.

so i herd talk of people thinking of doing a joule thief in the xbox 360 controller. but no tutorials anywheres i could find. so i pieced this together myself. this joule thief tutorial and another for LEDs in the controller.

how i have it setup now is a 1k resistor from the controller to the joule thief + input. and the - to the joule thief to the - on the controller.

then on the +s and -s on the output of the joule thief i put 4 x 5mm white LEDs.

the batterys in the test controller are completely dead. cant even connect to the console for more then 2-3 mins. yet the LEDs for ABXY are bright.

when im saying + or - im referring to polarity. and my joule thief is using all the parts listed above. just put together abit neater.

[1up]

That's probably not a resistor, then. And you don't need this for XBOX controller LED's. The 360 controller already has a 3.7v battery, so you just need a resistor for your LED's.

[RONEDOGG]

yeah lol thanks i was having a slow moment the other day. i figured it out. i forgot to have a resistor coming form the controller to the joule thief. got it all working now.

i just put another 1k resistor off the controller + before the joule thief

battery life at 1 bar and the LEDs are still super bright. now just to fit this troid into the controller housing lol

quick question 1up. if i wrap the troid more then the recommended turns will this improve brightness for 4-6 LED's?

[1up]

You're not listening. :P Don't use a joule thief. The 360 controller already has a 3.7v source, which is plenty enough to drive these LED's. A joule thief is for when you want to run 3.3v LED's from a 1-1.5v source.

Just calculate a resistor for your LED's and use that in front of them.

[RONEDOGG]

yeah lol im listening. there is one factor your missing. when the battery pack starts to die. the 3.7v is no longer 3.7v its more like 2.0v. so the LEDs dim. i used the right resistor and it did nothing. when the battery's were under fully charged. the ABXY buttons would dim. then by the time the battery got to half, there was no illumination to the ABXY at all.

dunno maybe i am missing something big here. i dont know anything about what im doing but i do know is the joule thief did fix the dim ABXY LEDs lol

If you google around people talk about similar issues with DIY ABXY LED mod on wireless controllers. thats why they mainly do it on wired controllers. because if the battery's for the controller are not fully charged the LEDs are considerably dimmer

I am wiring my LEDs in the controller on the positive and negative leads inside the controller.

Not sure if any of this is making sense to anyone. but i can post pictures and show what im talking about. its clear to see lol

[S33PlusPlus]

More turns shouldn't make a huge difference. I made one the other day on the same ferrite core (Dead CFLs are handy!) with ~20 windings of 30AWG magnet wire and I didn't notice improvement over my 12 turn toroid.

[ajain7]

Can ferrite out of adapter, which is square in shape, work? I used it with transistor named 13001 and a resistor but it was not working at all.

[ajain7]

Can ferrite out of adapter, which is square in shape, work? I used it with transistor named 13001 and a resistor but it was not working at all.

[rtty21]

the way the torid is configured steps-up the voltage, right?
Please explain to me what the torid does exactly. I really appreciate the time and effort you put into this project! Thanks for posting!

[jhao]

you could get a nice battery holder instead of soldering the wire straight to the tip of the battery :)