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Author Topic: What I learned in Joule Theif 101  (Read 16692 times)

d3x0r

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What I learned in Joule Theif 101
« on: February 09, 2012, 07:56:29 AM »
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.
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d3x0r

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Re: What I learned in Joule Theif 101
« Reply #1 on: February 10, 2012, 10:11:45 AM »
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 :)
« Last Edit: February 10, 2012, 06:04:33 PM by d3x0r »
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d3x0r

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Re: What I learned in Joule Theif 101
« Reply #2 on: February 10, 2012, 10:01:58 PM »
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)
« Last Edit: February 11, 2012, 09:18:24 AM by d3x0r »
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d3x0r

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Re: What I learned in Joule Theif 101
« Reply #3 on: February 11, 2012, 10:14:32 AM »
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.
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PhiChaser

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Re: What I learned in Joule Theif 101
« Reply #4 on: February 11, 2012, 04:35:19 PM »
@ 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
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d3x0r

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Re: What I learned in Joule Theif 101
« Reply #5 on: February 19, 2012, 01:53:54 PM »
Original schematic here... http://www.overunity.com/10179/joule-ringer/dlattach/attach/49957/image//
From the top, the transformer gets labeled 1, 2, and across the bottom 3,4,5,6
 
I've wound a toroidal transformer, that worked to light a neon from 0.02A... I wound a study coil, then took 12ft of 24gauge wire and doubled it back on itself 3x (1.5ft 8 strands) and wound them around a toroid.  I already had a length of wire for the primary, so most of this would be the secondary.  I then cut the loops and crossed them so I have lots of taps on the secondry. 
 
I have a 1-2.4k potentiometer and a few coil-caps that are almost 500pf each.  I have all 3 connected, At 122ohms, the wave is what I expect a joule theif to look like, a low spike on the base and a high spike on the high voltage out.  If I adjust the pot just a little higher, it snaps into an inverted high frequency wave.   If I further increase the resistance, the spikes continue to be inverted, but the freqency lowers, but the voltage is back up to normal.
 
The yellow line is the high voltage out, the probe is set at 10x and the scale is 2V, so each is 20V [this was spiking much higher, over 100V until something? happened].  The blue line is 2V scale 1x on probe, to monitor that I'm not pulling the base excessively low.   I'm thinking that this higher harmonic inverted thing is the lower power operation mode.  The current and voltage is 0.01A and 1.2V to start at normal spikes, then 0.01A 2.4V is jumped to when the pulses invert, then 0.01A and like 6.8V to have higher pulse voltages.  The interesting thing, is that it's a change involtage with the inverted pulses, where normally one would increase amps to get higher spikes.   
 
 
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