Picture of Making A Simple Joule Thief (made easy)
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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). 
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vmars3162 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)  vmars3162 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.
grimdaddy2 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)  grimdaddy2 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 :))))
richarno2 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
MakersBox made it!2 months ago

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

ASCAS (author)  MakersBox1 month ago


Can you post the circuit analysis? how does it work...
Thanks in advance

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

rjohnson652 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..


DangerousTim2 months ago


shaldar25 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
shaldar2 shaldar25 months ago
* BC547 correction
shaldar2 shaldar25 months ago
the polarity of the led is fine.

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

ASCAS (author)  mohammadsalem947 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? .

LAS10 months 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 :-)

Warmtint1 year ago
You need to improve your English. Thank God for the pics because the written instructions are nothing but confusing and impossible
ASCAS (author)  Warmtint1 year 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.
PhilKE3FL ASCAS11 months ago

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.
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