Step 4: Try it Out!

Picture of Try it Out!
Joule Thief Schem.PNG
And that's it! You're finished with your Joule Thief. Touch the twisted wires coming from your toroid to the positive side of a battery, and the extension wire to the negative side. If all is working well, the LED will light up! If not, try using thinner wire on your toroid. I've included a schematic in the pictures if you prefer.
nfhaines8 months ago

Help me understand the role of the transistor? Is this specific to the joule thief? Running and LED directly from battery source (with resistor) doesn't seem to require the transistor, so I'm curious about what changes with the joule thief to make the transistor a requirement?

DHeigh nfhaines6 months ago

My understanding: LED's require >3V to work. Joule Thiefs use one battery (1.5V or less) by charging the coil and adding its discharge to the battery's charge to power the LED.

The transistor does the switching from charge to discharge. The LED is actually blinking really fast like AC florescent bulbs do, but just too fast to see.

ppanchal16 months ago

Will using it reduce amps?? Please help.

X3msnake made it!9 months ago

Hard to see at first what is connected to what, I used parts of an old psu to build mine :)

ob103ninja1 year ago

What happens with a full 9v battery and 30 turns?

Wow , well it worked just fine with 10 wrappings around the toroid i managed to make a "dead" battery to light up a Led it couldn't before , pretty simple and useful instructable
P.S. Does it really reduce amperage ?
Cause im thinking of using it as a boost to run a motor
Jollyrgr2 years ago
Since I don't see it, I will add my two cents. The Base of the transistor connects to the resistor. The Emitter goes to the negative side of the battery.
rabitt2 years ago
hey man..what i nedd to change on this circuit if i want 10-20 leds....help¡¡
can i use hsd965 for transistor?
Ray Power3 years ago
Thanks for the instructable! I could only get 4 wraps on my CFL salvaged toroide but it seems to work
RONEDOGG4 years ago
i just tried this for a xbox 360 controller leds. and well it didnt go so well. i used the same size troid same transistor but my resistor was abit different. it was grey in color. and it heats up liek bad. enough where i have a blister on my leg where it fell. lol

any idea what transisotr to use for 4 LEDs?
1up (author)  RONEDOGG4 years ago
That's probably not a resistor, then. And you don't need this for XBOX controller LED's. The 360 controller already has a 3.7v battery, so you just need a resistor for your LED's.
RONEDOGG 1up4 years ago
yeah lol thanks i was having a slow moment the other day. i figured it out. i forgot to have a resistor coming form the controller to the joule thief. got it all working now.

i just put another 1k resistor off the controller + before the joule thief

battery life at 1 bar and the LEDs are still super bright. now just to fit this troid into the controller housing lol

quick question 1up. if i wrap the troid more then the recommended turns will this improve brightness for 4-6 LED's?
1up (author)  RONEDOGG4 years ago
You're not listening. :P Don't use a joule thief. The 360 controller already has a 3.7v source, which is plenty enough to drive these LED's. A joule thief is for when you want to run 3.3v LED's from a 1-1.5v source.

Just calculate a resistor for your LED's and use that in front of them.
RONEDOGG 1up4 years ago
yeah lol im listening. there is one factor your missing. when the battery pack starts to die. the 3.7v is no longer 3.7v its more like 2.0v. so the LEDs dim. i used the right resistor and it did nothing. when the battery's were under fully charged. the ABXY buttons would dim. then by the time the battery got to half, there was no illumination to the ABXY at all.

dunno maybe i am missing something big here. i dont know anything about what im doing but i do know is the joule thief did fix the dim ABXY LEDs lol

If you google around people talk about similar issues with DIY ABXY LED mod on wireless controllers. thats why they mainly do it on wired controllers. because if the battery's for the controller are not fully charged the LEDs are considerably dimmer

I am wiring my LEDs in the controller on the positive and negative leads inside the controller.

Not sure if any of this is making sense to anyone. but i can post pictures and show what im talking about. its clear to see lol
ajain74 years ago
Can ferrite out of adapter, which is square in shape, work? I used it with transistor named 13001 and a resistor but it was not working at all.
jhao4 years ago
you could get a nice battery holder instead of soldering the wire straight to the tip of the battery :)
robot13984 years ago
can i use a bc547 transistor in place of 2n3904
-max- robot13984 years ago
i used a transistor out of a flash camera, it worked. after playing a lot with it, i found the 2n3904 to be vastly superior. most other transistor didn't work or barely did.
robot1398 -max-4 years ago
i made it with bc547 and works better than 2n3904
-max- robot13984 years ago
great for you! i dont know if half the transistors i used were NPN or PNP. i think most were PNP
ShemySheza4 years ago
thanks but 1 question-how many wounds of wire?just 10 or can i use more?does it matter?
with most Joule Thiefs it doesn't matter. as long its more than 2 or so. the more windings you can fit, the better.
jtod4 years ago
How can drawing power OUT of a battery charge it up.? I don't make sense to me.
-max- jtod4 years ago
the dead battery still has a lot of juice in it when it wont power up stuff around the house. the Joule Thief will take advantage of that power and charge another battery of course it wont have more charge as the first. as the law of conservation states.
1up (author)  jtod4 years ago
Where did I say this would charge the battery?
lperkins4 years ago
It's perfectly possible to solder to batteries without any ill-effects. Commercial battery packs use spot-welding, and you want the heat characteristics to be as close to that as possible. Basically you want a high-power soldering gun. One of those little pencil irons is not going to cut it. In my experience, a good rule of thumb is to never put your iron to the battery for more than about two seconds, and then let it cool completely first if you have to hit it again. If you can't make it work that fast, you need a hotter iron. I can only speak for Alkaline, NiCd, and NiMh batteries. I wouldn't even try to solder things with "Lithium" anywhere in the name without good safety gear and a fume hood.
rayfalcon4 years ago
hey it works kind of! let me explain whats going on it blinks my led but will not keep it lit up and my battery gets extremely Hot so i quit using the one i just made and taking some time to try and get help on itthe 1 k trans might be wrong on mine its a clear glass thing with Brown black and red on it but its glass and on one side it says 48 thats all it has on it.....Is that a 1k trans or is this a diode? if so can that be the problem?
1up (author)  rayfalcon4 years ago
It's a diode if it's glass. :P Look up some diodes and resistors on Google images so you can tell the difference.
kcarring 1up4 years ago
+maybe it is a 1n4147 diode. resister shouldn't be glass. if it looks like this: http://tinyurl.com/27l63z6 it's a diode
rhanson2944 years ago
Not to be offensive, but I have always been told that you never solder to a battery. In some of the pictures it looks like the wire is soldered directly to the battery. Just wondering how safe that is.
I think that with a pair of magnets the soldering can be avoided. Just an idea to who wants to avoid soldering.
1up (author)  rhanson2944 years ago
It does looks like that. I actually slid the wire under the plastic cover on the battery to hold it in place, and the bottom wire is just being sat on by the battery.

You are right, you should never try to solder to batteries.  
anupamvipul5 years ago
it would be great if u add theory of coil used and diagram with colour
Blofish5 years ago
Outstanding detail!