Joule Thief

[gyulasun]

Hi Conrad,

Please allow one notice with respect to the output voltage, for you sound as if you were expecting more output voltage?  (If you don't, than sorry  )

Red LEDs forward voltage drop range between 1.7-1.9V or so and they are very good in doubling as Zener diodes because they can nicely limit the voltage across their legs when they sense forward polarity. So no surprise you see a near 2V_pp across it, the LED keeps collector AC voltage at its forward voltage level, cannot do much else... 
Just place a similar red LED in series with the first one (also in forward direction of course) and you will find a near 4V_pp voltage across them with your nice scope.
And if you increase the number of turns at the output to get an up-transforming turns ratio, then you may connect more LEDs in series but you surely know this.

rgds,  Gyula

[crowclaw]

To the Joule Thief Masters in this Forum!

I just built my first Joule Thief (and I know you moved way beyond that beginner level).


Greetings, Conrad

Hi Conrad and welcome, you'll find plenty of help and  support here for your project. Your circuit is fine... now try adding  another led(s) in series with the one you have!  and see how many more you can light! Spend some time going back through this thread to give you further inspiration for what you can do with this simple circuit. A single LED will light up to reach it's maximum working voltage after which point it's series current increases rapidly and the LED will then overheat and fail. The working voltage is generally up towards 3 volts depending on colour for standard LED's. Well done Kind Regards

[conradelektro]

Hello gyulasun and crowclaw !

Thank you very much for your help, and it helps a lot. I overlooked the voltage drop and will try more LEDs as you suggested. I will also experiment with different numbers of turns.

---------     What also puzzles me is the frequency.   -------------

---------     15 KHz seems to be rather low. Is this the impedance of the Toroid? How could I get a higher frequency?    -------------

I went through many posts and much was helpful. And I started the winding of a big coil for a "Slayer exciter". I found the forum GBluer(Slayer) Exciter. I am fascinated by the videos posted by Slayer and Lidmotor and I think a lot about Slayers circuit. It is simpler than the Stiffler thing, which I do not understand at all.

I am also aware of the experiments with a secondary on the Toroid, as was discussed in this forum and elsewhere (I collected many hints from the posts). I want to try that too.

It will take me a while to catch up to the level of this forum. But I got most of the stuff now (transistors, diodes, LEDs, enameled wire, neons, ...).

Thank you again, Conrad

[Pirate88179]

To the Joule Thief Masters in this Forum!

I just built my first Joule Thief (and I know you moved way beyond that beginner level).

May be one of the experienced Joule Thief experimenters finds the time and has enough pity to give me some advice?

Attached find a cope shot and and some information about my Joule Thief.

I wounder whether the 15 KHz indicate that everything works well? I only get 2 Volts over the LED from a 1 Volt AAA battery. Chanell 1 is the measurement over the LED and Chanell 2 is the voltage over the battery. It does not work with a 0.5 Volt battery, but a 0.8 Volt battery is enough to light the LED.

The Joule Thief is now running about 4 hours and the transistor 2N3904 stays cool (AAA battery about 1 Volt).

-----------------
The big question:  Did I put too many or too few turns over the Toroid?
-----------------

Greetings, Conrad

Conrad:

I see a potential problem with your JT.  First, you used a powdered iron toroid not ferrite.  Some of these can work ok, but some do not seem to work at all or with lower output.  Even if you used a ferrite toroid of known properties, if it was much different that what we were using back then, you would need to tune your circuit to the toroid.

In other words, the 1k resistor only works under certain conditions.  Hook up a 5 k pot to the base with no other resistor.  Adjust the circuit until you get the best numbers of whatever you are looking for be it low amp draw or highest volts out.  measure the pot and use this a your resistor value and remove the pot.  Or you can leave it in if you want and just use that.

Otherwise, it looks like a nicely wound JT there.  Your freq. is in the correct range so I suspect that when you adjust your resistance to the base, you will see better results.  This toroid may work for you is what I am trying to say, once you tune the circuit to it.

I hope this helps.

Bill

[jeanna]

Hi Conrad.
Yes, your jtc looks fine to me as well.
My guess on the 15Khz is it might be the toroid.
The elements of a joule thief circuit become complicated very quickly.

In my circuits I add another coil around the toroid and it is on that other wire that I can add many more leds in series.
In fact, I need to caution you about adding too many turns for one led.
I normally advise to limit the turns to 6 turns for the first led.
Then, add another and another until the led is bright.

Now, you can know how many turns you need to make for each led in series.
It is easy on most of the little toroids, like the one you used, to add enough turns to put 6-8 leds in series.

So, try adding a 6 turn pick up and see how well it does.
Oh remember that if the light does not turn on one way turn it around, because this secondary-pickup wire has a neg and pos side.

I assume you know that you must scrape off the varnish from the ends of the magnet wire before it will work.
(I am reminding all those others who are lurking and do not know to do this.)

jeanna

edit
I see many of us posted at the same time.
I agree with Bill, the blue toroid looks like a lower permeability toroid.
If it is giving 15KHz, you can try a secondary as I just described.
If it is low permeability you will need many more turns to get a dangerously high voltage, so give it a try.
j