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

[123awsomelad]

Can you just use a straight ferromagnetic core? or does it have to be a toroid?

[adien gumilang]

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 gumilang]

can i subtitute the toroid with the same-shaped magnet ?

[Jollyrgr]

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.

[colin55]

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.

[colin55]

circuit:
http://www.talkingelectronics.com/projects/200TrCcts/images/BikeFlasher-Amazing-1.gif

[rabitt]

hey man how i can conect 20 leds on this circuit....tnks

[rabitt]

hey man..what i nedd to change on this circuit if i want 10-20 leds....help¡¡

[m.halsey]

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

[blakdragon19]

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)

[mtuks]

i'm making a JT currently with a wrrist watch battery and you won't believe it..i'm revolutionising energy!! :)

[colin55]

Here is a Joule Thief with 10 LEDs on a 9v battery

[colin55]

Here is a circuit for 10 LEDs on a 9v battery

[DHeigh]

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?

[stringstretcher]

How do joule thieves work with lemon batteries?

[1up]

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.

[colin55]

(removed by author or community request)

[mittu gat]

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

[ctudoran]

Hello!
Can anyone tell me if I can use this circuit to light 5 leds (3V), but from a 2.4V input?
Thank you!

[1up]

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.

[bludlow]

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]

That'll be just fine.

[alindsey3]

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

[ssuman1]

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

[jason10kv]

ssuman1,you can't light up a led from salt watr,because the miliampere is very small.

[jason10kv]

hello sillyscript! you could try connections an be sure that the enamel on the wire is removed.

[Sillycrypt]

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

[buteman]

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.

[echuzzzzcute]

can i use hsd965 for transistor?

[echuzzzzcute]

is it okay that I use 2n3035 for high amp?

[emcelhannon]

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

[tylervitale]

Probably not. Joule thieves don't provide a lot of current. They work with LEDs because LEDs use very little current. A motor is likely to draw far more current.

[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.

[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.