Picture of 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?
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Step 1: Parts and Tools

Picture of 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
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.
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dONTbEdICK3 months ago

What effect does this technique have on a fully charged battery? can it fold up at the transister? Im a total noob so please forgive,

It will just be brighter. I actually took 2 rechargeable AAA batteries that had 1.2v in them and the LED shined really brightly.

ob103ninja7 months ago

What happens with a full 9v battery and 30 turns?


nfhaines13 days ago

Help me understand the role of the transistor? Is this specific to the joule thief? Running and LED directly from battery source (with resistor) doesn't seem to require the transistor, so I'm curious about what changes with the joule thief to make the transistor a requirement?

The LED will only light up if the battery voltage exceeds te forward voltage of the LED. Think of it as a threshold. So connecting a 1.5V battery to an LED with a forward voltage of 3V won't light it up. The Joule thief circuit here pulses the power through the coil, which causes a voltage spike, which is high enough to light up LEDs with a forward voltage much higher than the battery can provide directly. Furthermore, it can keep doing so untill the battery is almost completely drained, in effect 'stealing' every last bit of energy from the battery. It is so good at cranking up the voltage, it can work with batteries that are too discharged for most other devices.

X3msnake made it!22 days ago

Hard to see at first what is connected to what, I used parts of an old psu to build mine :)

mind power2 months ago

Can i use a transistor from an old CFl

colin552 years ago
Here is a Joule Thief with 10 LEDs on a 9v battery
colin55 colin552 years ago
Here is a circuit for 10 LEDs on a 9v battery
DHeigh colin552 years ago
I'm trying to fix a 3 LED, 2 D-cell flashlight, the LEDs don't light.
The circuit they are in has a 3-pin device labelled only "8N 11027" & a 2-pin device w/o any label.
I thought I might rebuild it with a joule thief that would work with 3 white leds off 2 D-cells. Can you help?
mjhearn DHeigh3 months ago

I'm a little late with this post, but built a pretty small (like dime sized) Joule Thief yesterday night, per 1up's instructions/suggestions. Used magnet wire suggestion, as well as the CFL toroid and the 2N4401. I say all that to say: for the LED portion of that circuit, i used a 3 LED lamp from a keychain light. The 3 LED's were VERY bright, powered with only a 'dead' 1.5V button cell (AG13?) and the JT.

adarshmodh6 months ago

hey i was able to make a simple working model bt wt i'm curious about is dat

1) wt effect would we see if change the no of windings ?

2) wt does it do exactly does it amplify the voltage, if yes then can we amplify a voltage of 3.5V to 5V by maybe increasing the no of windings on both sides....

please reply asap

suvinks6 months ago

Hello,When am trying, 1.3v Battery is providing only 1.2v across the LED and hence it is not lit up. Could anyone tell me where I might have went wrong?

Tried with 10, 11 and 12 turns around the toroid. Same result :(

mittu gat2 years ago
Hi my transister is getting rlly hot!! but the led lights up. i hooked up 1.5v battery......

Same here, I would like help with this issue if you have solved it.

I found out that there isn't really much you can do. Unless u want to add a heat sink. But what I did in my new version is that I glued the transistor to the bottom of the LED and this helps reduce the heat.

too much voltage and/or amperage going through. is it the same as the one in the instructable?

if not, you might be interested in getting the same one.

jneave6 months ago

spent an evening with the wrong two wires on the inductor twisted together. Made a hot transistor. Seems to require at least one volt but there we go.

ob103ninja7 months ago

Try cranking it up with 50 - to - 500 turns on both coils and attempting to arc it

jeidins8 months ago
weird thing happening. as I take AA battery at 0.8v it makes it 1.5v but when I take 5v joule thief makes no difference. any know why?
GreeceFallout9 months ago
Wow , well it worked just fine with 10 wrappings around the toroid i managed to make a "dead" battery to light up a Led it couldn't before , pretty simple and useful instructable
P.S. Does it really reduce amperage ?
Cause im thinking of using it as a boost to run a motor
GreeceFallout9 months ago
Can we use 2 separate toroids 1 for each wire ?
caruano95 made it!10 months ago

5 white leds, powering on a single AA battery.

chexin5111 months ago

I tried a GET5172 ( = NTE123A ) and the LED is the brightest yet. It consumed .1V from the single battery in 24 hours.

2N4401 lights better than a 3904

2N2222A doesn't light at all ? ? ?

chexin5111 months ago

The critical part of the winding the toroid instructions are:

Keep winding the two strands through the toroid until you have about 11 turns
We now have two pairs of wires facing opposite directions.
Take one wire from each pair ensuring they are a different color and solder this
"crossover pair" together. This goes to the positive of the battery.

PhilKE3FL11 months ago

None of these transistors can handle "amps" they are all probably in the 200 mA range. A 2N3904 is listed as 200 mA typical EC current I believe. But I'm sure most people will understand what you're saying. The other point is that while the transistor can push 200mA if 200mA went through the LED it would burn up in a very short time. Most of these LEDs are rated for around 20-30mA that's about one tenth of the rated current handling capacity of the transistor.

anishvr1 year ago
Hi, if we use a Germanium transistor AC128, will this still low the working voltage of circuit ?
ygupta11 year ago
Okay I made one. But how do I make the LED brighter?
Can you just use a straight ferromagnetic core? or does it have to be a toroid?
yes i can, but i just curious, i found these on my small electric motor, then i think, can i substitute the toroid with this?
um.. forgive me, i just a beginner
can i subtitute the toroid with the same-shaped magnet ?
Jollyrgr1 year ago
Since I don't see it, I will add my two cents. The Base of the transistor connects to the resistor. The Emitter goes to the negative side of the battery.
colin551 year ago
Here's a Joule Thief you can make from a fridge magnet. And it flashes:
This bike flasher uses a single transistor to flash one or two white LEDs from a single cell. And it uses a fridge magnet for the core of the transformer. This means anyone can build it with common components.
Cut a small fridge magnet into four pieces and make sure each piece sits the same way on the previous piece. The size of the pieces do not matter. 1.5cm x 1.5cm works well. Now wind 30 turns and then another 30 turns. Build the first circuit and connect the wires. If the circuit does not work, swap the feedback wires.
Now add the 10u electrolytic and 100k resistor (remove the 1k5). The circuit will now flash.
rabitt1 year ago
hey man how i can conect 20 leds on this circuit....tnks
rabitt1 year ago
hey man..what i nedd to change on this circuit if i want 10-20¡¡
m.halsey5 years ago
We made two and both aren't working. It's not the batteries, we tested on old and new batteries. We followed the instructions step-by-step. The only thing we can think of Is maybe the toroid coil wires? Is there a specific way the toroid coil's wire need to be to make it work? We have red and green soldered together and then the green soldered to the transistor and led light and the red soldered to the 1k resistor. 1st timer here. Thanks
yes, for the two leads that you coil together, they must be one of each separate coil (using different colored wire for the two helps here)
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