The Simple Joule Thief.

The Joule Thief is such an easy and simple device, but what it does is amazing. It can use a battery that is not usable in any other electronic device and give it life again. It can even take a battery that won't even power a basic LED by itself when it is brand new (1.5 volt AA) and amplify the power so that it can.

This "Joule Thief" circuit, using a battery that won't work in any other device, can power a blue or white LED for approximately 8 days straight before it stops working. It could probably power a red LED for at least 10-12 days. You could also use it to power a microcontroller (such as an AVR or PIC MCU).

This is an entry in the LED Contest with Elemental LED and the Hurricane Lasers contest, so if you like it, vote!

Step 1: Why Is It Called a Joule Thief?

The reason the Joule Thief is called what it is is because of what it does. (That sentence was confusing) (:

Basically, what the Joule Thief does is it "steals" every last Joule of energy from your batteries. The explanation of what a joule is can be found on the Wikipedia page here. The quickest explanation I can think of is that a Joule is a form of energy that, in the way we use it, can be used to power electrical devices. I won't go into any more detail here because it gets very complicated.

Step 2: Parts List

To make this "Joule Thief", you will need:

1x 470uH inductor (looks like a fat resistor)
1x 2.2K resistor
2x 1K resistor
2x basic NPN transistor (2N3904, 2N2222, 2N4401, etc.)
1x 1000pf (same thing as 1nf or 0.001uf) ceramic capacitor
1x AA battery + holder (or any other 1.5 volt battery)
As many LEDs as your heart desires.

Step 3: Make It on a Breadboard!

It is super simple to make on a breadboard because it has such a low parts count. Look at the schematic to figure it out.

Step 4: Make It Permanent!

I have included the .sch and .brd files for making your own PCB. You can send the .brd file to the OSHPark website here, and they will make 3 copies of the board for $2.30 with free shipping. Not even kidding, it's that cheap.

Step 5: It's Done!

See, wasn't that easy?

You can also use a 2x AA battery pack instead for enhanced brightness. I'm not sure how many batteries you can go up to until the LEDs burn out, but you can sure test it yourself! :)

Step 6: BONUS! Use It to Power Your Projects!

You can add this Joule Thief to any of your projects that use microcontrollers also! Add it to my LED dice project here and get a super-green Dice circuit!

You could also probably make a super-high-power Joule Thief power supply with a 9 or 12 volt battery instead!

Comments

[MadOverlord]

If you add multiple LEDs, do you install them in series or parallel?

[Robert Powell]

If you use a 2n4401 transistor you will burn out the led at 2.3 vdc because 2n4401 can handle more amps. But idk with 2n3904 or 2n2222 so idk. :-)

[pieniondz]

It wouldn't behave differently, because the current drawn by the diode is not going through the transistor, but you would be able to pull more power through the circuit (if the coil is ok with it of course).

[pieniondz]

If you were to power something from such circuit be sure to add a capacitor of at least doubled capacitance parallel to the output (in the same fashion as an LED). It will prevent voltage noise and without it the powered circuit i.e. microcontroller may not work.

Feedback on my suggestion is very welcomed.

[QUACKULLA]

hi there,

is it possible to make a joule thief that will work from 48 vdc -128 vdc and handle 500 amps?

anyone?

[chuckr44]

Yes, theoretically, however recall that powerin = powerout, or wattsin = (wattsout * ineffciency_factor), where inefficiency_factor is about 0.8. So if you want to boost volts you will lose amps in the process. So if you want to boost volts from 10vdc to 30vdc, you will have to start with input of 1875amps (1500amps/0.8 inefficiency_factor) and end up with around 500amps.

That's a lot of amps!

[chuckr44]

Thanks for posting the equivalent values of things, like the capacitor in picofarads and nanofarads for us newbies. While I enjoy electronics I just don't have the time to do it enough to get good at it. My main jobs is as a software guy. :)

I've also seen other designs that use only one transistor.

[gizmologist]

One joule = one watt for one second. It is a unit of work as is a kilowatt-hour. How is that complicated??

[JRV31]

Mine lit a red LED for nine days.

[JRV31]

I built another Joule Thief instructable using a self wound coil. As soon as I get the choke I'm going to build this.

It's based on the same principal as the fly back diode attached to a relay.

[Technobly]

Was my comment deleted?

[hypery11]

i use 2N3904 as the transister, but it doesn't work!!

[the radio man]

nice project im doing it now unfortunatly i dont have LOL only have 1 red and im happy i can power it for more than 15 days (because im not using a dead 1)