Making a Simple Joule Thief (made Easy)




Introduction: Making a Simple Joule Thief (made Easy)

About: Hi I'm Angelo! I am a college student taking my engineering majors in BS-EE/ BS-ECE at the DLSU. I use my course as an inspiration for making my current projects! I've been posting projects here ever since I...
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:

Step 1: 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). 

Step 2: Schematic Diagrams

Here are the schematic diagrams that are involved with the joule thief circuit.

Step 3: Winding Wire at the Toroid

First, connect both ends of the copper wire before wounding, be sure to remove the insulation. Then try to solder the ends so it would not split up. Second, wind the wire until you run out of space in the round ferrite toroid. I have some tips for you, try to use a gauge #22 enamel coated copper wire for better performance, oh! my last tip is that "the more you wind the wire to the ferrite toroid the better".

Step 4: Soldering the Resistor

Solder the resistor with one end of the wounded ferrite toroid's wire. Oh! also don't forget to level the other end of the resistor with the other unused wire from the wounded ferrite toroid.

Step 5: Soldering the Transistor

Solder the proper connections to the transistor. For the emitter - connect another wire, the wire will be connected to the negative part of the battery. For the base - solder the other end of the resistor to the base. For the Collector Solder the unused wire of the ferrite toroid.

Step 6: Soldering the LED

Solder the shorter wire of the LED to the tansistor's emitter and the longer part of the LED to the transistor's collector. After all that, you can now trim the excess wires.

Step 7: Time to Look for Old Batteries

Use your battery tester to confirm that your battery is close to death. The tester is only an optional tool, it's just used to determine the battery's remaining power.

Step 8: Time to Test It - You're Done !!

The wire connected to the transistor's emitter should be connected to the battery's negative side and the remaining wire of the ferrite toroid should be connected to the battery's positive side. Oh! one more thing, I advise everyone to use a battery case or attach a conductive magnet for each wire, so you wouldn't hold it all the time.

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128 Discussions

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.

5 replies

There are pre-made dc-dc step-up convertors with a USB port already on them. Try this one: Input voltage is 0.9v to 5v, output is 5vdc. Easy peasy.

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 :))))

I have the topic as my school project but the problem is that the project looks too small. is there any way to make to big.

Actually if you added a capacitor in parallel with the transistor you probably could power a 6 volt device. But the pulse width would probably be so small it would still appear to be turned off.

Actually scratch that, you'd need to use a zener diode. To power higher voltages you need higher frequencies. This means lower switching potential is needed, and a lower capacitance. Lower capacitance than a diode is a tough one.

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?

1 reply

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.

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!

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 :)

1 reply

Question 4 weeks ago

Hello, this question is a bit urgent. How can I connect more than one LED to the joule thief?

can the wires be aluminium?


1 year ago

Hi Nice project.......

I am not from an electronics background, but I am wondering if this could be used to power a string of LED Christmas lights.

I guess you would need to use a fresh battery and change or add some components to up the voltage.

I am looking at a very simple circuit, this looks like it may do it, I would be interested in your thoughts

Thanks again

Is it possible to use conductive tape instead of wires to make it more compact? Or does it HAVE to be the copper wires?
Just wondering so I could make it sturdier and more compact.
Love this idea!

On one of your pictures near the top of this 'ible it looks like a circuit with a pre-made joule thief on it. Do joule thieves come pre-made? I'm having trouble finding spare parts to make one. I just don't have a lot of parts laying around.


1 year ago

does the copper wire have to be coated?

1 reply

usually copper wire made for transformers has a transparent isolation layer

well done! I love your instructables! :)