What I learned in Joule Theif 101

[d3x0r]

The sound is too loud   And I forgot to make background music

http://www.youtube.com/watch?v=NUxtlLohSmQ

Futher notes here from what I learn I suppose; Has to be somewhere.  For instance, what is the actual effect of shortening or lengthening the collector side of the coil or the base side of the coil, in either case, the pulse width shortens.... when the current is the limiter on the circuit, more current decrease the frequency of the pulses (unless you're using stranded iron, then you apply more current and you get shorter pulses, until you get to a maximum at which point the pulse width widens, and the overall effect is strengthened.... higher voltage output but slower pulses... at a certain point of power, it flatlines (core saturation?  transistor overpower?)....

Just some noted empirical results, more objective notes later.

[d3x0r]

I have a lot of images of various scope shots and various states and an analysis of small numbers of windings.  (like 100 of them , so that would be like 10 messages, so I guess I'll have to keep this short and simple.
First, and it wasn't where I started... what's the smallest windings you can have with a joule theif?  One.  If you have a straight wire with power applied in the middle, and run it through a toroid, you get 0 effect. (maybe balancing the resistor and transistor you would have a standalone oscillator.  If you remove the coil entirely, it also doesn't work, but that goes back to a standalone RT oscillator of some sort).  I started thinking it was 1/2 because it's really 1/2 winding to collector and 1/2 winding to base... and it is joined in the middle so one.

1 winding (1/2 winding to base and collector) is 725khz
2 windings(toward base) is this is 2.5V swing, almost double ( 2 windings instead of 1)  515khz
2 windings to base and 2 to collector 200khz
6 windings (3 windings to base and collector (2.5?)) is  132khz
12 windings (6 windings each to base and collector is 64khz)
12 windings is about 8 inches of wire.  for this particular core. (with about 1inche leads out )  (Reminds me, I should do the same experiments with a larger diameter core).

(I think I forgot to reverse the 2:1 coil to collector and base instead... so I have to do that and a larger toroid).  I'm sure there's a few hundred details I wanted to note

[d3x0r]

I realized that I didn't really test the most minimal configuration. 
1) a wire with the power connected in the center, run through the toroid.  (does not work)
2) the same wire, folded in a U around the toroid.  (does not work)
3) the same wire, crossed on the outside of the toroid, so there is at least one loop.  (does not work)
3.a) turning that so the shared connection is on the outside, and the wire is crossed on the inside of the toroid.  (this works); so you need at least one through the toroid towards the base and one through the toroid to the collector.


(actually, not sure about the power connection... not sure about the changes moving the power center point... I would think cannot put it... on the ends for sure(?).... [given what I learned below, I would imagine that having the power connection inside would shorten one side or the other and allow for tuning, still have to test that]

Fewer windings on the coil connected to the collector increases the overall frequency, fewer windings on the coil connected to the base shortens the length of the pulse generated, but decreases the overall frequency [there would no longer be fewer windings on the collector side in comparison, so the frequency goes down]

The same count of windings on a larger toroid is the same frequency as a smaller toroid (? only tested with one winding each, should scale windings up too)

[d3x0r]

Frequency depends on toroid size, a larger toroid will be a lower frequency.  Tested Originally with single winding configuration, and got same frequency for both 2.5" and 1" toroids... but that must have been an observational error.  Tested several directions from number of windings in the core 10:10 (measure frequency at a power level), and also matched length of coils through the center which is more relational to the toroid size... (if toroid a is 20mm high, and a second is 8mm high... that's 2.5x diffence so I wound 4 on the big and 10 on the small, and got similar voltages, but the smaller toroid had a higher frequency.  Applying lots of stages of power, will eventually get long chains of spikes that are very short (retriggers quick). (like 2.5V 0.6A).. but applying even more power reduces the back spikes present and increases the frequency a LOT, so output is very diminished.

I would assert though, that the same length of wire through the center of the toroid generates the same voltage spike.

[PhiChaser]

@ d3x0r
Thank you so much for your pics and notes!! I haven't built a joule theif yet but my current experiments will require one somewhere down the road. Very useful information to anyone working on JTs!
Great job, thanks again, and keep experimenting,
PC