Picture of Making A Simple Joule Thief (made easy)
images copy.jpg
Today I am showing you how to make a very simple joule thief. A joule thief has many applications, the best gadget that I made with was a "Water Powered Lamp", soon I'm going to post on a guide about it but first I need to post this guide. I used an iPhone 4S as my camera :))) 

What Is A Joule Thief ?

To simplify everything, a "joule thief" is a circuit that helps drive an LED light even though your power supply is low. What can we do with it? We can use it to squeeze the life out of our old, almost drained, non functioning batteries. This project can also be considered as a green and environmental experiment, we can also use it as a flashlight that can be ran by an old, weak, almost drained battery. I even tried to use my water powered battery from my previous instructable the "Water Powered Calculator", the project was featured and displayed in instructable's front page in the "Technologies" category.

My Next Projects That Involves A Joule Thief: (soon to be posted)
- Water Powered Lamp
- Water Powered Flash Light
- Dead Battery Drainer Lamp


Here's A Video From Make Magazine:

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Step 1: Parts And Materials

Picture of Parts And Materials

The Parts Needed Are: (click the item to know where to find/ buy)

- Round Ferrite Toroid (can be found in old CFL bulbs)
- Old/ Used Batteries (can be found in garbage cans)
- NPN Transistor (2N3904)
- 1K Resistor (BRN-BLK-RED)
- LED Light
- Battery Tester (optional)
- Soldering Lead
- Copper Wire/ Magnet Wire
- Battery Case/ Holder

I want to share something. Here in the Philippines electronic parts are extremely cheap, they are extremely far cheaper from
radio shack, for example one transistor costs (2 phil. pesos - 6 US cents), a LED cost (9 phil. peso -  29 US cents) and a 1K resistor cost (25 phil. cents - 0.8 US cents). I usually buy thing from Deeco or Alexan. Usually prices here are 15x cheaper from radio shack. Price conversion - $1 US Dollar = P0.31 Philippine Peso (12/24/11). 
vmars3163 years ago
Very cool project.
I am just learning about electronics:
could this same 'circuit type' be used for a
"free energy" from radio waves project?
Could someone, more qualified than me, design such a circuit?
ASCAS (author)  vmars3163 years ago
Harnessing radio-wave frequency and turning it into electricity is not that efficient.
Good luck! One of my first projects in electronics was the joule thief, since it is easy to construct.
grimdaddy3 years ago
I am not a electronics guy and I have a few questions.
1:What happens if you hook this up to a new battery?
2: What happens if you hook it up to a three volt cell?
3:Could this be adapted to a 1watt Led that runs on six volts?
4: Could this be adapted to a flashlight, more specifically a tactical flashlight?
This looks like an idea that could go places.
ASCAS (author)  grimdaddy3 years ago
1. It will have a longer battery life
2. The LED would wear out/burn
3. this circuit is not designed for that/ there are other circuits for that.
4. Yes. I made a flashlight out of it.
Good luck :))))
richarno3 years ago
You got my vote!
Thanks for this nice instructable.
great project! Always wondering what to do with the old batteries i had laying around. im glad im not the only 13 year old doing projects like this. Try my 12 volt varyable power supply project! Thanks!
oanderson3 years ago
Nice Instructable, very useful for the novices out there and the more advanced tinkerers! I see your next project is a lamp, I check this one out: I'm thinking of making one :)
ASCAS (author)  oanderson3 years ago
thanks for the comment and reply :)))) Hope you luck :D

will a BC 547 or 557 will work?

and if not in which item i can find a 2n3904

larry.rivard made it!2 months ago
made it.
larry.rivard made it!2 months ago
I made it on a breadboard. I found the toroid in a retired network switch power supply. I wrapped the toroid with 22 gauge solid wire. This is a great project and instructable. I will post it finished once soldered.
shaldar28 months ago
can anyone please tell me the problem i have used bc337 transister i have used bx547 kn2222A as well but it didn't worked out please help me where i am going wrong
kentuski shaldar23 months ago
you should connect the beginning and the end of the other wire
kentuski shaldar23 months ago
you have a wrong polarity of wire,,,
shaldar2 shaldar28 months ago
* BC547 correction
shaldar2 shaldar28 months ago
the polarity of the led is fine.
clchee made it!3 months ago

I couldn't get 2N3904 so I substitute it with 2N2222 instead and it works. My soldering isn't the prettiest but it works !

Check it out

MakersBox made it!5 months ago

I made a circuit board for it and added a switch. Makes a great night light.

ASCAS (author)  MakersBox4 months ago


moez.elmassry4 months ago
Can you post the circuit analysis? how does it work...
Thanks in advance
MFarrasalifm4 months ago

Hey, i saw the "mini version" do you have the instruction for that? i really need it. Thanks

rjohnson655 months ago

Very simple design can use any "Common NPN type transistor" ie 2N3904, 2N2222, 2SC945, BC546, MPSA06...

But it would be slightly better with a 47uF cap across the battery...

10 to 100uF and 3 to whatever voltage... Size is the limit... really..


DangerousTim6 months ago


great job... but how that's work when the battery is death???

ASCAS (author)  mohammadsalem9410 months ago

It depends on how drained it is. This circuit drains the battery completely to zero.

it's doesn't work. i use BC337 transistor? .

LAS1 year ago

On your schematic the coil has dots on opposite sides of the core, indicating that it is wound from opposite directions.

Your pictures show that you "double wound" the coil, starting both from same side.

To have the "double wound" pictures fit the Schematic, opposite ends of the "double wound" must be tied together, red from one end to black of other end :-)

Warmtint2 years ago
You need to improve your English. Thank God for the pics because the written instructions are nothing but confusing and impossible
ASCAS (author)  Warmtint2 years ago
I'l try my best to re-update my words/ instructions. Thanks though, for reminding me. It was a challenge for me to write ible guides since I posted this when i was 11 and English isn't my primary language.

I think you did a very good job. It was obvious English was not your native language as it would be for me if I tried to write an Instructable in German. I even lived and went to university there for a year when I was in my early 20's but now I'm in my 60's and it has been a very long time since I've written or spoken German. At age 11 I think you've done an outstanding job! Updating the instructions, as your English improves, would be big help for, and I'm sure appreciated by, those for whom electronics isn't all that familiar.

PhilKE3FL1 year ago
What is the voltage drop for the LED I have two types 3V & 6V ultrabright LEDs will this work for them?
Would a 9011 transistor work in place?
It looks awesome... using this we can make a new 'radiation harvesting' system
syedj941 year ago
How much voltage is it outputting?
ASCAS (author)  syedj941 year ago
About 3.6 volts
Schmidty161 year ago
Where do you get the toroid and could u just use a magnet that is in the toroids shape
ASCAS (author)  Schmidty161 year ago
I tried to drill a hole on the magnet's center and it didn't work.
The toroidal cores are very abundant in CFL bulbs, specifically in their balasts.
Oh cool looks like ill be taking apart lights what else can i scavange in them
ASCAS (author)  Schmidty161 year ago
You can pretty much make a joule thief out of a torn apart CFL. The only thing needed is a general purpose NPN transistor, the best example is the 2N3904.

You can find a variety of:
- Mini Transformer
- Toroidal Cores
- Tons of Resistors (1k included)
- Dozens of Capacitors (H.V.)
Schmidty161 year ago
Im trying make this out of grabage what can i find the 1k resistor in
Or can i use another kind of resistor
Schmidty161 year ago
Does the joule theif also make the led emmit a brighter light
Can you link to a place selling suitable toroid? Taking apart a CFL really isn't the best option for me.
Any ham radio store or electronics shop should carry a wide spectrum of toroidial cores.
Good point.
Its true that the RF ferrite toroids for low frequency rfi filters (hf) frequencies are low permiability, but the toroids used in the Microwave bands (a very large part of the hobbie now) and the toroids used in switching power supplies, are high permiability, even some using neobendium toroids as chokes.
Many ham radio operators often build their own radios and amps, and power supplies etc. Those working in the microwave frequencies, usually build the bulk of their radios, due to the high cost of commercial microwave radios.
Toroids lose there inductance as the frequency increases, so rare metal ( neo) toroids work much better in high frequencies
Another good source are toroids used in defunct neon sign circuits.
That was an excellent idea, to use the CFL toroids, as reusing those tiny toroids keeps one more thing from the landfills.
On a side note, Ive switched from cfls completly, to LED lighting, saving the toxic chemicals and horrendous fluctuations of life time, in CFL's, caused by cycling the on off schedule of CFLs. CFL bulbs should only be used in lights that only get turned off and on once a day. normal multiple on off daily cyclces of CFLs, cause failure in CFLs in about a year. I think LED lighting actually makes CFLs defunct.
A great idea for an instructable how to video, might be the rescue of toroids from dead CFLs.
Thanks for the great info. :-))

I don't need to visit any website to tell me what I already know. I've had the same thing happen to me as what Canoeman stated. Turn CFL bulbs on and off and end up with a dead CFL.
eventually when you discard old lamps or circuitry, keep some of the toroids...
ASCAS (author)  activenowhere3 years ago
coolest thing
to make
Utsav252 years ago
Can I add a capacitor or another transistor somewhere to increase the output power so that the LED glows more brightly?
ASCAS (author)  Utsav252 years ago
Probably no, you will need to completely redesign the circuit
Utsav25 ASCAS2 years ago
OK. I'll try it out .Do you have a schematic that you can provide?
Utsav252 years ago
Very nice project works great .!
dash243 years ago
is it ok to used an any kind general purpose npn transistor instead of what you used there?
Goodwin73 years ago
Nice instructable, I find it helpful, thanks!
nerj3 years ago
Good instructable's for all enthusiast, keep it up.
For my joule thief, can i use zinc wire instead of copper? Is there a difference in performance if zinc wire is used?
ASCAS (author)  Aperture Laboratories3 years ago
Yes. It would be fine.
oh good,that was all i had laying around:)
does it matter what npn transister you use?
ASCAS (author)  project_builder3 years ago
Just choose something similar. Also consider the fact that different NPN transistors also have different arrangement of the terminals.
Jordan Dyck3 years ago
hmm? i'm thinking my transistors dead
luig3 years ago
hello i have been trying to make one but i didoes work. yes i assembled just like it says in the diagram, but is there something else that could keep this from working? for example what would happen if i put many more coils on the Toroid. what if the emitter and the collector are backwards etc.
Acmefixer is right on the money! I was wrong in identifying the oscillator as a resonant colpitts. It is in fact a blocking oscillator with a square wave output. The biasing isn't right to allow it to oscillate resonant, because the frequency would have been up in the tens or hundreds of Megaherts. This oscillator is going at some frequency under a couple of thousand Hertz. Sorry, that I got you so riled up - my intention was not to mislead.  I thank you that you weren't so mad that you ignored my desire to be set straight.  It's no shame to be wrong once in awhile.  The trajedy is to stay that way and go through life with blinders on.  Thanks again .
ASCAS (author)  luig3 years ago
try following the video.
luig ASCAS3 years ago
ohh i just found found out that the led works at 4.5 volts could that affect this project?
dagob3 years ago
Can someone explain the theory behind this circuit?
Is it applicable to 9,6V? I know the circuit must be reconfigured for 9,6v usage, but if it is possible, could someone point out here how to do it?
The circuit is an oscillator - specifically, a transistor,Colpitts oscillator. If you look at the classic Colpitts oscillator circuit you may ask," Where are the capacitors?" "Nowhere in this instructable does our brother mention any need for capacitors." There is capacitance. It is the capacitance between the wires that are being close, and tight-wound over the ferrite core. Remember, two things: first, a standard, passive capacitor is merely two conductors in a circuit separated by a non-conductor - be it air, mica, polystyrene, polycarbonate, or air or a vacuum- in this case, the insulation of the copper wires; secondly, an oscillator oscillates at a frequency determined by its' passive components, so even if you may think that this capacitance is so small that your capacitor meter isn't even registering it, you can figure that this circuit is oscillating at a very high frequency, and doesn't need much capacitance. That is why the author said that if you wind more turns on the coil it seems to get better. This is because the frequency is coming down into a more manageable range for the transistor, and there is a more optimum storage of power in the increased windings of the coil. This circuit is being operated as a flyback transformer in a boost configuration, meaning that the voltage of the weak battery is being augmented by the back-EMF (high spike voltage) from the energy stored in one-half of the two coils that are wound on the ferrite as the transistor oscillates. Well, where is the diode as are used in other flyback transformers? It is the LED, which is a lossy diode in the sense that it doesn't supply power to some other circuit, but uses all the available power itself to waste as a micro amount of heat, and to convert into light energy. Of course, without a measure of the inductance of the coils, you're blindly ignoring the maximum operating characteristics of the LED and transistor. Does the circuit work? Clearly , yes. May the output voltage be too much for the LED, or exceed the transistor's specs? It might. When you have properly made circuits, you just follow a recipe and do what it says, and it pretty much works. If you want to learn something, research the specs of the transistor you're using, and the formulas that govern the operation of the Colpitts oscillator, and you may find that along with an oacilloscope, you may find that you may have to adjust or add components to make everything last a long time. If you are a scrounger and can't get the transistor from your junkbox to work, learn how to identify an NPN from a PNP with a meter, and for your particular transistor, how to identify the Emitter, Base, and Collector. The wrong hookup will either cook the transistor or just not oscillate. An oscillator is just an amplifier with feedback, so if it doesn't oscillate, you may have to adjust the resistor. Don't give up if it doesn't work. You don't learn anything, if everything is given to you and you don't have to exert research and sweat to gain better understanding of what you're doing.
People have been using the ambguous phrase 'joule thief' which basically means nothing. In order to explain an ambiguously named circuit I tried to relate it to what has already existed for years in the common realm of electronics by means of the earliest use of a specific class of switching power supplies - the flyback transformer. As such, the flyback power supply would take the relatively low, full wave direct rectified line voltage of 164 VDC and add to it the output of the oscillating coil, rectified through a high-frequency power diode to minimize losses through the diode.This is how you got your 250 volt and higher plate voltages for tubes without having to have bulkier input power transformers. Of course the energy in a coil is stored in the magnetic field but it is unnecessarily splitting hairs to say that one must specify this for inductors, and yet if one discusses capacitors, you dont have to mention the electric field or the chemical composition of electrolyte for electrolytics, or the physical geometry of the plate effects in super capacitors. If further explanation is required, I wait for uncertainty to arise before addressing the concern further, otherwise the discussion could take the place of an instructable in itself. I would be interested in your analysis of the circuit, as to what you say the existing class of oscillator it is. An inductor is useless unless it stores and releases energy. To do this it has to cycle or oscillate at some frequency, and basically, 'it's all been done before". It has to fall in the class of some existing oscillator.
kostya3 years ago
I've built a dozen of flashlights around this schematic using BC547 as an NPN transistor. They work well but efficiency is low. If electronic parts are so cheap in the Phillippines you may try to buy Zetex LED drivers. They are a bit tricky to solder being smd-components but adding a ready-made inductor and a resistor you will have a highly-effective flashlight.
I prefer Zetex ZXCLD381. Here it costs under .5USD. It is a bit tricky to solder because it is smd. The other day I built a micro flashlight around this chip, an inductor(resistor-like) - 22uH and a white LED.
ASCAS (author)  kostya3 years ago
Its true. But I am teaching the other people, mostly the beginners, to learn more in a slow instructional process :\\
Perhaps, instead of decrying someone's choice, you might state why you have different idea and why your idea might work better.

Perhaps you have access to a wide range of components. Other might not.

Perhaps you have access to technical information, and know how to use it. Others might not.

Perhaps you have technical training. Others might not.

It's always better to educate rather than criticize. A few well-chosen comments will enlighten and encourage!

Sorry if this is largely a duplicate; instructables doesn't have an edit option as some forums do. Just delete and post again. No doubt there applications where the higher collector current capability of the 2N4401would make it a better choice, but respectfully this is not one of those applications. Using a nearly spent battery to power a LED or as in the Make video making it possible to power a LED that requires 3 V. from a 1.5 V battery. While it can certainly varies, in general a LED requires 20 mA, a transistor that can handle more than 200 mA is not require here . You seem to be suggesting we should expect the 2N4401 should perform here better than 2N3904 based on a single criteria that doesn't matter, you appear to be that pot calling the kettle black.
I capish the tech..

But this young man is 13. I do not know what part of the globe he calls home. he may not have RS access! He has been interested in electronics since he was 4 and I absolutely applaud his efforts!

I am long retired with old degrees in electrical/electronic engineering. I have never heard of a joule thief. I read the 'able because I was curious.

Perhaps you could send this fellow a bag of transistors to help him develope his talents...
I've had good luck using the 2N3904, or 2N3906 with polarity reversed. But I also parallel the resistor with a small capacitor (a couple pF is good) which helps the transistor turn off a lot faster, which helps performance whatever transistor you use. Also, if you use a 2N3904 with a full alkaline cell, a 2k resistor is appropriate to avoid exceeding transistor specs.
If I understand the Schottky diode correctly, it has a very low turn-on voltage (in the forward direction) which will let the positive pulse start sending current into the capacitor where it accumulates until the LED turn-on voltage is reached. When the pulse goes negative there will still be some usable charge in the capacitor that would otherwise be dumped to ground. Sound reasonable? Anybody got a spice model to run?
So your 'scope observations see no improvement with the Schottky+ capacitor in the circuit? Sometimes the output of the coil can be considered as a 'current source' in which case it would be pushing current into the capacitor that is already charged up to the LED's required voltage. Your 'scope shows what's happening -I'm just trying to understand the 'Real World' like everyone else is. ;-)
The diode + capacitor give a more steady current to the LED, which makes the LED more efficient. But that is countered by loss in the diode. Hard to be sure how much of a net win it is.
From your second reference:
"Note that most of the modern ultrabright LEDs have close enough to maximum efficiency at currents near or below their maximum rated current. If your average current through each LED is around or over 20 mA, use steady DC. It does not pay to pulse the LEDs when the average current is around or over 20 mA."

Pulsing increases efficiency with very low average drive current or the older inefficient LEDS.

Using a 2n3904 in a joule thief, and a resistor selected to limit peak current to 200mA, you're getting a 200mA peak current to the LED without the diode and capacitor to convert the pulse. That comes to the neighborhood of 30mA average current, 100mA average during the pulse, ~30% duty cycle depending on driver efficiency and battery voltage.
"without the diode and capacitor to convert the pulse" the current through the inductor has nowhere to go except the LED when the transistor turns off. In a properly operating joule thief the current through the side of the transformer connected to the transistor and LED follows a fairly neat triangle shape between zero and peak. When the transistor conducts, current in this inductor increases. When the transistor turns off, this current decreases feeding the LED.
The plot where you measured collector current by putting a test resistor in series with the emitter shows a problem. For the circuit to work well the collector current needs to snap off quickly, like in the later spice plot. The soft transistor turn off you measured would sap efficiency and result in peak LED current much less than transistor current. A capacitor in parallel with the resistor, as I mentioned earlier, helps with the fast turn off. The ferrite used for the inductor could also make a difference.
The Schottky diode is used because of its low voltage drop and fast switching ability. Both of these are good for efficiency. But of course there does have to be SOME loss involved.
ashy33213 years ago
hey can any body explain the use of 1k resistor in this circuit and what if i cut it off
keroroman3 years ago
Instead of using a battery case, can I use some electrical tape to hold the wires in place?
ASCAS (author)  keroroman3 years ago
or_ford983 years ago
wow, thats a really nice camera for a phone :O
ASCAS (author)  or_ford983 years ago
Yeah! The picture is resized, meaning the original file of the picture is much better. I love the iPhone's camera, it takes picture like a SLR camera. I suggest you buy one.
or_ford98 ASCAS3 years ago
lol im definately not going to buy an iphone 4s or a d.SLR camera.... but i sure like them!
ASCAS (author)  or_ford983 years ago
If you have money to afford a Nikon D7000, I suggest you buy one. My dad has one and it works great!
or_ford98 ASCAS3 years ago
well i found a place to buy iphone 4s cameras lololol XD
luig3 years ago
I am curious can this work on dead 6 volt batteries. you know the big ones that they use for lamps?
ASCAS (author)  luig3 years ago
yes! but it will only work when the batteries voltage is around 0.3-1.5 volts.
Ace Frahm3 years ago
Is there a practical use for a joule thief? Lighting LED's with a flat AA battery isn't the best use, so I'm wondering if it can be scaled up to start a car with a flat battery etc..
If I may, I would like to suggest a site that discusses alternative construction and components, and has tips on how to get your joule thief running,
HandySun3 years ago
The thing I like about this is the blue light indicating the jewel thief action is kinda hard to see. If it was RED the whole world would see whats going on with your toy
sgoldberg3 years ago
Very nice work and excellent pictures and explanations.
keep it up!
build-mat3 years ago
It very much impresses. But there are questions. Esteem also here these articles: Too it is a lot of interesting.
ASCAS (author)  build-mat3 years ago
Sorry. But I don't know that language.
At the risk of showing abysmal ignorance, I didn't know what CFL bulbs were, (Thank you, Wiki) so could I just add that, for people like me, CFL means Compact Fluorescent Lamp. How very nice to find that parts of them can actually be useful!
would be nice to see an instructable that takes an old battery and drains it into a storage trap of some sort that could be used to recharge the batteries that can handle a recharge using a similar process to the joule thief
Kante Tech3 years ago
Yes I understand the fundamentals of resistors for I had already build like 3 but what i was wondering is can you use a fresh battery instead of a drain battery? For i think that a fresh battery will probably drain out or something.
ASCAS (author)  Kante Tech3 years ago
Yes. You can use a fresh battery. I've tested it and it will have a longer time lighting the joule thief compared to the old one.
ASCAS (author)  acmefixer3 years ago
Thats true :))
souichi3 years ago
isnt 1us$ = 50 philippine peso? but then this comming time it becomes P43

and yes electronic stores here in the philippines is very cheap i make alot of projects with electronics..

nice instructables.
ASCAS (author)  souichi3 years ago
Yesterday, I was shocked because the conversion was around 1us$ = 31 php.
icekid3 years ago
I see you made another project of yours! I already made a joule thief but it gave me a hard time making it because some guides in the net are incomplete but yours is extremely complete and fully illustrated.

Keep it Up! Nice work!
I find subscribing with you very useful. Thanks a lot with your cool projects.
bigjeff53 years ago
It's winding, not wounding. To wound the toroid you'd need to hurt it in some way, and I don't think such a thing is actually possible for an inanimate object.

Yes, the toroid is wound, but you had to wind it to make it wound, you didn't wound it. If this is incredibly confusing, this should help clarify things: wound, the past tense of wind; and wound, the act of injuring, are homographs. They are spelled the same but pronounced differently, and have two entirely different meanings. They aren't even the same tense.

Wind and Winding are the words you want here, not wound and wounding.

ASCAS (author)  bigjeff53 years ago
I'm sorry I did that 12:00 midnight waiting for Christmas, my brain seems to be dull :)))) I'm so sleepy. Don't worry I'l change that.