The Joule Thief

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

Comments

[aarchbold]

aarchboold ask
We have had lots of power autage lately therefore id like to make several joule thief but before i make the inductors I`d like to know what wire you recomend as the best- What type, number . If thicker or thinner is better. etc
Thanks

[blinkyblinky]

I suggest this: magnetic 58930-a2

Whether or not you can use it is a question. I used CAT5 cable (solid)

Any torroid will work as long as you wrap a lot of turns. As long as you purchase a torroid like in the picture below...to me, color and size don't really matter but I could be wrong.

[acmefixer]

Actually there are many grades of ferrite, from very low permeability to very high mu (permeability). For a Joule Thief you want a toroid that has high permeability, because it allows you to use fewer turns of wire and keeps the DC resistance of the wire low. The DC resistance should be much less than 1 ohm. You should be able to get enough inductance with 7 to 20 turns of wire. Get some Fair-Rite 2673002402 cores from Mouser.com, they work well for experimenting and only cost 12 cents (U.S.) apiece. Get a few feet of 24 AWG (0.5mm) solid insulated wire from an old telephone cable. You can use the wire inside of a cat5 cable but it's a lot kinkier and harder to unwind. I get about 10 turns of two windings on this size core.

[aarchbold]

aarchbold ask:
I got the same torroid in your picture so I´m on my way and I understand that the more turns the better.
Thanks.

[blinkyblinky]

You're welcome.

[acmefixer]

One other thing I forgot to say. Without the resistor, the high current will seriously shorten the battery life.

With the right transistor and resistor, you can light up 5 or more LEDs brightly. Some of the right transistors are: KSD5041, KSC2500, 2SD965, NTE11. These transistors are made for handling high current - several amps. The 2N3904 is a poor choice for a Joule Thief, its rated at an absolute maximum current of only 200 milliamps.

[recuat]

can i know how is the circuit go on this transistor? is that using the same circuit? KSD5041, KSC2500, 2SD965, NTE11

[acmefixer]

The same but you will have to experiment with different values for the resistor and number of turns on the coil to fit the number of LEDs.

[blinkyblinky]

My sentiments exactly.

[blinkyblinky]

Yes you just need to play around with values to get it to work a LONG time.

[blinkyblinky]

What I had on hand.

[recuat]

why the step 4 picture circuit is difrent from your given circuit?
can i have that circuit so can drive many led instead 3, thanks

[blinkyblinky]

No, no, no... :)

That picture with the big transistor and ic is not related to the thief in any way whatsoever. It is an organ I never finished. I just needed a large breadboard. I don't know the number of LEDs or the power each one consumes so stick a potentiometer where the 1k resistor should go and find something you like by adjusting the values.

[Treknology]

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

[blinkyblinky]

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.

[Treknology]

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

[blinkyblinky]

2*30

[recuat]

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?

[blinkyblinky]

1. I think it is AWG 24.

2. I used a 1 inch (2.535cm) diameter ring.

3. "Ferrite" not "ferric" core ring.

[buteman]

If you connect a diode from the positive end of the LED's to a small capacitor with the other end of the capacitor connected to the transistor emitter I think you could measure the voltage across the capacitor you might see the the peak voltage ( less the voltage drop across the diode )

[blinkyblinky]

Smart...but diode lowers voltage.

Very good idea.

[aarchbold]

well, I´m just a bigniner but I´ll make mine and comeback with results.
Thanks for your instrucctios,
Alarchbold

[blinkyblinky]

You're welcome and good luck!

[mikolynn]

I got an "BC547 Transistor in TO92". Can I use it?
And I got a recycled inductor like this one:
http://media.digikey.com/photos/Bourns%20Photos/08412.jpg
Can I use it? And how I can connect it? because it have 4 pins, not only 3...
Thanks!

[blinkyblinky]

Yes and no. I tried a transformer recently but that didn't work and so, I would stick to Ferrite Cores. I read about using a nail would work but that also failed with me.

Your BC547 should work just fine...just make sure you check which pin is which.

[mikolynn]

Ok, Thanks!
But this is not a transformer, it seems to be one, but is an inductor...
Well, I try to make an inductor with an speaker magnet.
+1 point for you! ;)

[blinkyblinky]

Make sure you use the ferrite core. If you want, take apart an old radio and use the ferrite core to wind it together. I have not tried this method so let me know if you do.

Good Luck.

[mspinks]

I was curious about the resistor so I've been reading about it for a while from various sources. So far, from what I can gather is that the resistor is there simply to protect the transistor. According to the wikipedia article on the joule thief, with a very small load the voltage "may rise to more than 100 times the supply voltage." This would exceed the transistor's base-emitter voltage limit and cause a transistor failure.

[blinkyblinky]

Well then, I guess leaving out a resistor for high power applications would be fine.

[Magnelectrostatic]

Only if the transistor can handle the power, or the voltage. With a circuit like this you are more likely to exceed the maximum voltage rating on the base than the maximum power rating.

[blinkyblinky]

I thought about it and I came up with this:

What is power? Power is voltage x current. If there is extremely low voltage say...0.5 volts...and 15 amps of current, then the power is 7.5.

However, if voltage is high and current is low, like in solar panels, then power is also low. If I had 15 volts and 0.5 amps then my power would still be 7.5.

Now, if I had high voltage as well as current, then the transistor may blow such as 15 volts and 15 amps...it equals 225.

However, if I had lots of LEDs, then there would be much less current because each LED steals some current. That's why I put them in parallel not series. In series, each LED takes the voltage it needs and then passes it on. However if one light blew, all of them would blow. In parallel, the LEDs try to all pull whatever they can. However, if I have lots of them and they all pull all they can there would be less current for the transistor to dissipate.

I know what you mean though. When I left out the resistor and had one LED, I heard a slight whistling sound. as I added more LEDs the whistling sound slowly died down.

[davidbachman2028]

I have heard about the whistling sound on other joule thief designs, and the source is usually the inductor. The changing current flows can cause the windings around the ferrite to vibrate slightly and produce a high pitched noise.

When I have built joule thief circuits I normally put some hot glue on the inductor to stop the noise. It has worked for me.

[blinkyblinky]

Thanks I will add it to this ible.

[mspinks]

A whistling sound? Very interesting. I may to build this soon so I can experiment a little.

[blinkyblinky]

Sort of like a high-pitched squeal only able to be heard by younger people...very quiet too...

[Higgs Boson]

without the resistor my transistor got very hot. I've noticed this happen in other circuits, but especially this one. Did you have that problem?

[blinkyblinky]

Yes it does. User acmefixer said some pretty true things. (below)

How many LEDs did you use? I left out the resistor because I was going to power lots of LEDs for a long time.

What types of LEDs did you use (color) and what voltage are they rated at?

What type of transistor did you use?

These questions will help me access your problems.

[Higgs Boson]

only used two ultra bright white LEDs. that was probably the problem. But I did use the 2N3904.

[blinkyblinky]

As I said above:

What is power? Power is voltage x current. If there is extremely low voltage say...0.5 volts...and 15 amps of current, then the power is 7.5.

However, if voltage is high and current is low, like in solar panels, then power is also low. If I had 15 volts and 0.5 amps then my power would still be 7.5.

Now, if I had high voltage as well as current, then the transistor may blow such as 15 volts and 15 amps...it equals 225.

However, if I had lots of LEDs, then there would be much less current because each LED steals some current. That's why I put them in parallel not series. In series, each LED takes the voltage it needs and then passes it on. However if one light blew, all of them would blow. In parallel, the LEDs try to all pull whatever they can. However, if I have lots of them and they all pull all they can there would be less current for the transistor to dissipate.

I know what you mean though. When I left out the resistor and had one LED, I heard a slight whistling sound. as I added more LEDs the whistling sound slowly died down.

If you use a bunch more it should work.

[ernie666]

Check out the micro ferrite core that I used