Joule Thief 101

[Magluvin]

Honestly, I could slice and dice your technical comments apart if I wanted to.  I think that you are just being a poseur throwing out some technical terms and making a tired worn-out resonance play.  Why don't you sketch out various "resonance" waveforms for Magluvin ahead of time so he knows what to expect and where to look for them?  Why don't you explain the multiple resonance instances that you alluded to and explain where they are and what and where each of the two resonating components are in each instance?  Or do you just want to sit back and watch the experimenters fiddle with pots and comment when you think someone has "struck" resonance?  Why should an experimenter have to "hunt" for resonance and find some "special delicate balance" if you have been pitching it all this time?  If I strike a bell it resonates.  What kind of "special" or "remarkable" results should Magluvin and others get if they "strike resonance?"  What are they supposed to see?

If Magluvin or anyone else succeeds in achieving something remarkable with a Joule Thief in "resonance" and explains what is actually taking place instead of just observing something, I will be happy to admit that I was wrong and acknowledge that something special is taking place due to the resonance.

On the other hand, if all that Magluvin or others can get is mushy wobbly scope traces that are difficult to explain and don't clearly show "resonance" and yield unremarkable power-in to LED-illumination-out results (or any other metric you want to define), what are YOU going to do?

MileHigh

Well like Smoky said, it has to be fine tuned to search for resonant nodes. They could be within very tiny adjustments of the pots and could pass and miss it if not careful, and I totally understand that.

Mags

[MileHigh]

Well like Smoky said, it has to be fine tuned to search for resonant nodes. They could be within very tiny adjustments of the pots and could pass and miss it if not careful, and I totally understand that.

Mags

Yes that sounds fine and like I said, I am not really going to be involved in the resonance discussion.  The question of how a Joule Thief works in its normal operating mode has been answered and there was enough information covered over the past two weeks such that all the information is there if you want to do the reading and the research.

But at least let's look at a rough mechanical analogy for a resonant circuit and this would also apply to a hacked Joule Thief running in some kind of resonant mode.

Suppose you are in a museum and you come across a kinetic sculpture that demonstrates resonance.  You are looking at a big box-like open-air metal frame.  Attached to the frame are all sorts of springs with different sized weights attached, there are thin rectangular metal bars attached to the frame on one side only, bells, tuning forks, sheets of tin, and so on.  It looks like a small metal junkyard in 3D space and it stands about 10 feet high.  It looks like a shambles.

You can see how the base of the metal frame sits on four big springs.  There is a big variac that allows you adjust the speed of a 1/2 horsepower motor.  You notice the motor is in the center of the sculpture off to one side and there is a big off-balanced flywheel attached to the motor.

So when you play with the variac the spinning flywheel on the motor shaft makes the whole thing shake into a frenzied shambles at different frequencies.  You find different resonant frequencies for different things on the sculpture as the the whole crazy sculpture shakes and rattles.

However, you notice at each resonant frequency that whatever component is resonating will reache a certain maximum resonant amplitude and THAT'S IT - the sculpture doesn't shake it self apart and explode.  Rather, different components reach a maximum resonating amplitude where the losses equal and balance out with the supplied power - balance.

The sculpture never shakes itself apart because the resonating components always have losses that burn off the supplied vibratory mechanical power coming from the motor-flywheel.

And any electrical circuit operates in EXACTLY the same way.  A resonating Joule Thief will simply reach a resonant amplitude where the resonant AC currents will burn off power and be in balance with the supplied power.  In other words, a resonating Joule Thief will have a TON of i-squared-R looses and that will take power AWAY from lighting the LED.

The whole concept of a "resonating Joule Thief" is not exciting at all.

But I will leave it up to the experimenters to determine that for themselves, or I will admit that I was wrong the whole time if credible remarkable results are reported.

MileHigh

[Lidmotor]

I replicated Tinman's low voltage circuit today and it does run well below 200mV.
https://www.youtube.com/watch?v=Eup3iaHS5Oo
I used an MPSA18 instead of a 2N3055.  Maybe this will help you guys and maybe it won't but it was pretty cool seeing an led light up at that low a voltage.  Thanks for the discussion going on here. It is very interesting.

-----Lidmotor

PS --I asked my friends Hewey, Dewey, and Lewey if they they like to resonate. 
All I got was a blank stare.

[tinman]

I replicated Tinman's low voltage circuit today and it does run well below 200mV.
https://www.youtube.com/watch?v=Eup3iaHS5Oo
I used an MPSA18 instead of a 2N3055.  Maybe this will help you guys and maybe it won't but it was pretty cool seeing an led light up at that low a voltage.  Thanks for the discussion going on here. It is very interesting.

-----Lidmotor

PS --I asked my friends Hewey, Dewey, and Lewey if they they like to resonate. 
All I got was a blank stare.

Thanks for the replication--great job as always

Brad

[tinman]

Magluvin and other Joule Thief enthusiasts:

  I think that we have all seen similar scope captures of Joule Thieves running at very low battery voltages in the past - but most people have never seriously questioned what they were looking at.  Clearly something different is happening and it's happening at a much higher frequency than the normal operating frequency.

So do you just observe this, or, do you try to explain it and understand it completely?  If you can figure it out and explain it will you will get some satisfaction from that and in addition perhaps that new knowledge will give you more insight into trying to get a Joule Thief to resonate?

The good news is that you can slowly lower the supply voltage and observe how the waveforms change and that will help you a lot in determining what is taking place.

MileHigh

I reattached Magluvin's second scope shot to this posting.  Clearly a Joule Thief when running at a very low battery voltage does not operate in the standard switching mode as shown in his first scope capture.

MH
You do understand that a JT circuit is meant to operate at very low voltages?. I mean,that is what the JT is all about--taking the last bit of energy from an almost dead battery. Why are you talking about standard switchmode operation,when we are all talking about how the circuit operates at the low voltages we want them to run at.

I certainly can't explain what I am seeing.

Post 316-Quote: You mentioned stuff about transistor junction capacitance and "RLC."
Of course you cant,as you refuse to accept that the circuit !is! an RLC circuit. As long as you continue to exclude the C in RLC,then you will never understand as to how !your! JT circuit can run on voltages well below that of the threshold voltage required to switch on the transistor.

Take another look at Mag's scope shot that has you confused. What is the threshold voltage required by the transistor Mag's is using to switch on?. If the supply voltage to the JT is 320mV,then how come we see a higher voltage during the on time portion in the scope shot?.

Dont panic MH,i am putting together all the information you required from me on the workings of a JT !!at low voltages!, as that is what JT's are all about. Yesterday was just a big headf--k day,as i had doctors appointments,Xrays--all that crap. But i'll be back onto it today--just doing the video and scope shot's to go with the explained workings of the JT (your JT) circuit.


Brad