Make a Joule Thief

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.
jeidins19 days 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?
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
Can we use 2 separate toroids 1 for each wire ?
caruano95 made it!2 months ago

5 white leds, powering on a single AA battery.

mittu gat1 year 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.

chexin512 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 ? ? ?

chexin512 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.

PhilKE3FL3 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.

anishvr5 months ago
Hi, if we use a Germanium transistor AC128, will this still low the working voltage of circuit ?
ygupta110 months 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
adien gumilang11 months ago
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.halsey4 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)
i'm making a JT currently with a wrrist watch battery and you won't believe it..i'm revolutionising energy!! :)
colin551 year ago
Here is a Joule Thief with 10 LEDs on a 9v battery
Here is a circuit for 10 LEDs on a 9v battery
DHeigh colin551 year 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?
How do joule thieves work with lemon batteries?
1up (author)  stringstretcher1 year ago
Do you mean how well do they work? It certainly should work. You may need more than one lemon to get at least 1v, though.
colin551 year ago
(removed by author or community request)
ctudoran1 year ago
Can anyone tell me if I can use this circuit to light 5 leds (3V), but from a 2.4V input?
Thank you!
1up (author)  ctudoran1 year ago
You can hook them up in parallel, but there may not be enough current to light them all very well. You could put resistors on each of the LED's so they only draw a few milliamps, but that may still be too dim. You should try and see.
bludlow1 year ago
Is there any problems with using a 1.1k Resistor rather than a 1k resistor as i have only 910e and 1.1k resistors in that kind of area, thanks.
1up (author)  bludlow1 year ago
That'll be just fine.
it should be fine, check the voltage coming out and based on your led choose a correct resistor needed to lower the voltage enough for the led
ssuman12 years ago
Hello will joule thief be able to light up n LED from salt watr
ssuman1,you can't light up a led from salt watr,because the miliampere is very small.
jason10kv1 year ago
hello sillyscript! you could try connections an be sure that the enamel on the wire is removed.
Sillycrypt1 year ago
Hey i made this with a BC337 transistor & a xbox toroid but i doesn't show any signs of working? what could be wrong! thanks
buteman1 year ago
I have just built a joule thief following these instructions and it works well. I used a BC549 transistor rather than the 2N3904 as this is what I had. I used a toroid from a CFL bulb with 5 turns of wire. It will light 2 white LEDs wired in series so I tried using red LEDs in series and it would still light 10 of them in series although with that many they were not very bright!
I have seen lots of comments asking it a transistor type BCxxx 2Nyyy ( you get my drift ) would work.
I would suggest that anyone asking can easily find out quickly by using google search.
It needs to be an NPN transistor and if you search for say hsd965
you will find it is an NPN transistor. check which pin is collector, base and emitter and connect them as explained in this instructable.

The only time you might get a problem is if the gain ( Hfe ) is very low.
The hsd965 is quite high power and it's gain is high too.

If it still doesn't work then assuming you have all the connections made you should try reversing the connections for ONE of the wires. In the picture above for example swap the 2 orange connections over.

Hope this helps.
can i use hsd965 for transistor?

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