The Joule Thief

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Introduction: The Joule Thief

About: I love building things and taking pictures. If you want me to build something...I'm open to ideas. My motto? "If you want something to be done in this world, you must do it yourself.

The Joule Thief. I found this device on accident. I was searching for a WORKING decision maker and found this on accident. It can power many LEDs.

The inevitable: I make an instructable on: the Joule Thief.

This is a great circuit to teach children about electronics especially inductors and coiling considerind it contains so few parts and is so easy to make...

Let's get started.

To get us started, I have a video.

By the way: I had forgotten to put the arrows for the LEDs...sorry.


Step 1: Materials, Materials, Materials

You will Need:
3 ultrabright white LEDS
1 "dead" battery (with 1 volt left.)
1 2N3904 Transistor
1 jumper
1 handmade inductor or two pre-made. 
1 Solderless breadboard

Step 2: The Inductor.

Which one should I pick???There are thousands!

Well, I think you'll stick to the one in the second picture.

The 4th photo and beyond is courtesy of Evil Mad Scientist Labs. When I was making mine, I didn't realize that I had used enameled wire instead of colored CAT cable wire.

Step 3: The Circuitry.

Once again, I thank Evil Mad Scientist Labs.

Anyways, I omitted the 1k resistor. I don't know what it does but for now, i just know that I can power more LEDs. It might have something to do with current supply. If you know, please leave a comment.

So, build according to the schematic. Just remember, the two tabs that are tied together are the same tabs that connect to the positive of the "dead" battery.

Step 4: Fin.

Once you have built it, sit back, relax and enjoy the show that these LEDs put on.

One "dead" battery will give you about 65-70 hours of constant use. If you only use it at night then you would have a lot more time.

As always...if you experience any problems leave a comment and I will try my best to help you.

If you did make it successfully well then...leave a comment saying you made it successfully!





Step 5: Troubleshooting.

The problem with this circuit is that troubleshooting is virtually impossible unless you have a scope...

When I used a multimeter, it showed 1.2 volts going into the white, 3.6v LED. (The battery was 1.3v.)

A scope would show you the pulses though...

Well, there's not much I can explain about this circuit...but I'll do my best if you have any questions.

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    83 Comments

    Hi,

    What changes do I have to do to connect 12 LED's?

    Best Regards,

    Marujju

    I'm trying to make a Dodecahedron (12 sided polyhedron) Christmas ornament, with each face having an LED lighting it up. How do I hook 12 LED's safely into this circuit. Do I still use the 1K resistor?

    10 replies

    Note I think a third inductor should increase voltage going into the base or emitter for that type. I got it going with on AAA cell with a couple of electrolytic caps one being 1200 uf. And a 10pf to the base and a third inductor was place in the circuit. Oh well.

    One more thing, I have this joule thief running an un modified solar led light and so far it stayed on for most of the night. I would count said AA cell nearly new as it may have had 1v or better.

    Yep, just put how ever many LED's in parallel and choose the right battery capacity.

    Well, I would, but space is limited where they are going. A "C" battery is the largest that will fit.

    My other problem is that I was planning to hook up self-flashing LEDs to get special effect, but the pulse of the circuit seems to be resetting the LEDs' built-in circuit. How can I hook up a capacitor to maintain an operating voltage on the LEDs?

    I've tested this circuit with a C battery, and so far it's lasted 4 nights running close to 6 hrs each..

    Connect a small diode to the collector of the transistor, then connect the positive of a 100uf capacitor to the output of the diode, and connect the negative of the capacitor to the emitter of the transistor, then connect the positive and negative of your LEDs to the positive and negative of the capacitor. If it doesn't light up at all, check the battery, if the battery is good, make sure your joule thief isn't shorted out anywhere and that you connected the capacitor the correct polarity, remember, the positive lead goes to the collector and the negative goes to the emitter, if it still doesn't work, try reversing the diode or using another diode. If it STILL doesn't work, your joule thief might not be strong enough to run with a capacitor and you build another, with more powerful components. If it light up but still flashes and malfunctions, then try a bigger capacitor, such as a 220uf capacitors a 330uf capacitor, if it still flashes and malfunctions, try a 470 if capacitor, be sure that none of the components are overheating, if they overheat, replace them with higher power components. If it still doesn't work and you have tried all of the above tips, smash it, and build another, with high power components!! Maybe instead of small LEDs, you could use 100 watt LEDs, with big heatsinks and use high power TO3 transistors!!

    Connect a small diode to the collector of the transistor, then connect the positive of a 100uf capacitor to the output of the diode, and connect the negative of the capacitor to the emitter of the transistor, then connect the positive and negative of your LEDs to the positive and negative of the capacitor. If it doesn't light up at all, check the battery, if the battery is good, make sure your joule thief isn't shorted out anywhere and that you connected the capacitor the correct polarity, remember, the positive lead goes to the collector and the negative goes to the emitter, if it still doesn't work, try reversing the diode or using another diode. If it STILL doesn't work, your joule thief might not be strong enough to run with a capacitor and you build another, with more powerful components. If it light up but still flashes and malfunctions, then try a bigger capacitor, such as a 220uf capacitors a 330uf capacitor, if it still flashes and malfunctions, try a 470 if capacitor, be sure that none of the components are overheating, if they overheat, replace them with higher power components. If it still doesn't work and you have tried all of the above tips, smash it, and build another, with high power components!! Maybe instead of small LEDs, you could use 100 watt LEDs, with big heatsinks and use high power TO3 transistors!!

    The 1k resistor is technically optional because all it does is limit the amount of current that can flow into the base of the transistor (it's a good idea/practice to include the 1k resistor however). When adding in LEDs, all you have to do is wire all of the LEDs in parallel. Keep in mind that the 2N3904 transistor can only supply a limited amount of current (0.2A) so if you plan on using a large number of LEDs, you may want to use a transistor that can supply more current like the 2SC1384 (1-1.5A) or a darlington transistor like the TIP110 (2-4A). You may also want to try high voltage power transistors that are commonly found in CFL light bulbs (I've never tried using them) like the KSE13003 (1.5-3A).

    Okay, another crazy question: can the 2N3904 be used in parallel to increase current capacity? Since the transistor is voltage controlled, being in parallel won't affect their switching on (altho, differences in sensitivity might).

    What do you think?

    The answer to this question is actually more difficult than I thought it was; I didn't know you could do such a thing until I researched it just now. However, in doing so you may have to be quite careful because one transistor will often try to draw a greater amount of current which will cause it to heat up, causing it to draw more current, causing it to heat up even more, etc. In order to try and resolve this, you can connect them in parallel like you said, but at the emitters of each transistor put a 0.6-1 ohm resistor.

    It is probably better to just use a single transistor that can handle a greater amount of current. However, if you are in a rush it is a viable solution, just risky.

    Thank you.

    Buying the high-current transistors is not possible right now, but I have plenty of 2N3904 in stock.

    Have not had any success at all in replicating this experiment. I suggest that you need more that a 1:1 wind on the toloid

    As you were winding your enamel wire in a pair, how many turns did you actually put through the core?

    6 replies

    The large one with the Green wire I had put as many turns that would fit (About 30) The smaller one I had tried to do the same but it didn't work out because I ran out of wire. Oh well, guess I have to get more.

    So does that mean that you ended up with 2 * 15 windings or 2 * 30?

    1==please explain what is the gauze of the wire?
    2==what is the diameter for the ring that you use?
    3==magnetic ring or ferric core ring?

    I would never use a magnetic toroidal core for a Joule Thief. The output might blow a hole in the universe, or just not work the way you planned it to work.

    The Large Hadron Collider created fears of punching a hole in the fabric of the Universe and it hasn't done so, well, not so far as we've noticed. Although I've never seen a toroidal magnet (the round ones from Microwave ovens are face-to-face), I don't think that on a domestic level it achieve much apart from stuffing up the rest of the circuit.