Joule Thief

[conradelektro]

Attached please find a summary of what I could do with a lot of help from many people in this thread. It took me about a month from total ignorance to lighting a 5 Watt CFL with a Joule Thief circuit.

The result has a little flaw, because the circuit swings at about 6 KHz and produces a faint screeching sound that can bother people with good hearing and pets.

Bill (Pirate88179) can raise the frequency by attaching a neodymium magnet to the toroid. This helps, according to measurements I have done, it raises the frequency by a few Kilohertz. Gyula (gyulasun) explains that the magnet lowers the original permeability of the toroid and such raises the frequency. Unfortunately this does not seem to be enough to get the frequency beyond 40 KHz or better 100 KHz.

This is only a concern when one goes for a really high Voltage on the secondary, like 1200 Volt, to drive CFLs. In the range of Voltage for LEDs, about 50 to 100 Volt, I did not observe screeching.

According to what I have seen (e.g. in the thread about the Slayer007 GBluer Exciter), air coils offer an alternative.

I will now try some air coils and would like comments from experimenters who have done work with air coils in a Joule Thief type circuit. (Innovation_station gave me some hints on air coils, and I will implement that soon.)

A concern I see with Slayer Exciter type circuits is the electromagnetic radiation that could cause trouble with radio transmission regulations and may also influence the health of people in the vicinity of the circuit (for instance when using it for a reading lamp).

So, what do I want?

-   a Joule Thief type circuit or Slayer007 GBluer Exciter type circuit
-   with an air coil
-   that swings at a high frequency (more than 200 KHz),
-   can light a CFL nicely (about 1200 Volt) with an 1.5 Volt battery,
-   does not screech and
-   does not radiate too much.

The size of an air coil does not put me off. A nicely wound air coil can be a design feature attracting the attention of onlookers. It would be a retro 19 century look!

Well, fellow experimenters and masters of the electronic art, what can we do?

Greetings, Conrad

[electricme]

@ Conrad,

Nice work you have done here, well done on the research also.

jim

[Pirate88179]

Conrad:

I could be wrong but I believe the folks that tried air cores found that the efficiency was no where near as good as with a decent ferrite toroid.  As I said, this was a while ago and I may be incorrect about this.  I look forward to seeing your results with the air core and, by the way you document and present your experiments, we will all have some good data either way and learn something.

Keep up the good work.

Bill

[jeanna]

@Conrad,
You have done very nice work.
It is very gratifying to know that you cut the learning time by nearly one year from us. I like that too. Thank you.

I think you can resolve the screeching with some hot glue on the wires without hurting the effectiveness of the coil.
I never got around to that, so I do not know, but lasersaber did this for waterproofness and it works for that.

Please let us know how the air core is coming along.
I once used a ferrite stick that fit inside a weavers shuttle bobbin which I had wound with many hundreds of turns. The difference was really startling; the ferrite makes a big difference.

jeanna

[detrix42]

@conrad:  I am very impressed with your presentation, and your results.  i do not have access to oscilloscopes, or a frequency counter.  I want to tune a jTC to around 175kHz.  I prefer to do this with an iron core if its possible.   175kHz is supposed to be the resonance frequency of the Earth's magnetic field.  resonating at that frequency, according to theory I am currently reading about, can cause some interesting effects.  But I don't have the equipment to figure out the proper windings, and size of toroid.  Would you be willing to try to get a JTC up to 175kHz?

Detrix42