Is joule thief circuit gets overunity?

[MileHigh]

Bill:

I made the effort to explain to you what's under the hood of your JT.  No resonance at play, it's just the tuning of the oscillator and it's all about the size of the inductance and how much current is flowing though it when the JT transistor switches off.

Do you have any comments?

MileHigh

[TinselKoala]

@Plengo... thanks for the comments, I really appreciate the positive feedback.
The CH 2330 is a sampling instrument but uses a unique methodology at high resolution (16 bits).

From their website:

UNIQUE SAMPLING APPROACH / ISOLATED INPUTS
The Voltage and Current inputs of the Model 2330 watt meter are simultaneously sampled (with 16 bit resolution), converted to digital form, and transmitted via optical links to the main chassis. This allows both the Current and Voltage inputs to be completely isolated from each other and from the main chassis. The asynchronous sampling frequency is controlled by the system microprocessor in such a fashion that neither it nor any of its harmonics can come close to the measured input frequency or any of its harmonics. This precaution prevents "beats" with their accompanying jitter in the displayed values.

http://www.clarke-hess.com/2330.html

The instrument has a practical limit of 600 kHz for the basic signal IIRC; it will still be accurate on smooth signals at higher frequencies. Signals with fast risetime spikes will have a lot of power (relatively) in high-frequency harmonics, and so these are best measured with calorimetric or bolometric instruments. But the JTs we are using here, with frequencies in the tens of kHz and minimum risetimes of tens or hundreds of nanoseconds _seem_ spiky .... but that's a relative measure after all.
I used to be able to find a report of EarthTech's test of a Clarke-Hess 2330 against their extremely accurate calorimetric systems, and the two tracked almost perfectly, but I can't remember what the power specifications or the load were. I can't find that document now, the ETI website has changed drastically since I last visited it. But I would trust the readings from a CH2330 on the JT circuits we are discussing, until demonstrated otherwise. Note that the inputs and outputs are optically isolated and so presumably wouldn't disturb the JT LS GhostLight circuit like normal probes do.

I might be able to borrow a CH2330 from some friends of mine, but I'd have to drive 200 miles to do it, and I'm not up for that right now. Let's see what we can come up with using "TKLabs Seal of Approval" analog power measurement tech, ported to the DSO that Lawrence is using. If we still are getting massive OU after that, then I'll go get the CH and we can see if we can fool it too.
BTW it handled the 1.4 MHz "Tar Baby" just fine, gave numbers that agreed with my analog scope and manual calcs, and also with the actual performance of the DUT.

[Pirate88179]

Bill:

I made the effort to explain to you what's under the hood of your JT.  No resonance at play, it's just the tuning of the oscillator and it's all about the size of the inductance and how much current is flowing though it when the JT transistor switches off.

Do you have any comments?

MileHigh

MH:

First, thanks for the reply.  And second, I do have a comment on your response.  I still tend to disagree that when hitting the "sweet spot" it is not resonance as you say, just the most efficient configuration for that system.  The reason I disagree is that the results do not appear to be linear....this is hard to explain but I will try....In other words...when tuning the circuit using the base vr, as I am sure you know, you add more resistance and the bulbs get brighter and brighter and then, the almost explode in an order of magnitude in brightness....turn a little more and....they dim very sharply.

This has been my experience and, I can't explain it other than claiming that by tuning that circuit, i hit a resonance node of some sort.  I am trying to say that when you hit that spot....if you are careful, you get so much more out than you thought you would.  Just a fuzz more and you are back climbing down the opposite of how you climbed up in a linear fashion.  So, I feel there is something else happening since it is suddenly not linear just at that sweet spot.  If you were to graph it using the accepted info that you know so well....you would see a nice even curve going up and then, a huge jump off of the paper, and then and nice even curve going down.  If resonance is indeed the incorrect term for this event, I guess I would need another term to use in its place.  If all were linear, I would just say that I have tuned the circuit to the best efficiency.  It is that major jump that stands out so well that confuses me.

Thanks for the reply.

Bill

[TinselKoala]

Lawrence, can you give me specific details about how you are measuring and calculating your _input_ power, or rather energy, please?
Are you monitoring the voltage and current used to charge the capacitor, or are you using the values obtained from measuring the voltage waveform on the capacitor and the current waveform in the Current Viewing Resistor while the circuit is running?

Properly, you should be using the former, that is, the energy used to charge the capacitor  between running intervals.

So you charge the cap to the voltage of a power supply or battery. Its energy is then (CV_init²)/2. You then run the JT circuit for your timer interval. Then you  measure the voltage on the cap again, and the energy remaining in the cap will be simply (CV_final²)/2. The difference between these two values is the energy the cap supplied to the JT circuit proper, and can be compared to the total energy output of the JT (the integral of the output power curve during the time interval). (C in Farads, V in Volts, answers in Joules.)

But is that the whole story? What about the energy used to charge up the cap in the first place? Is it the same as what we measure as the energy "on" the cap that it can supply?  This you measure in the usual manner with an inline CVR in series with the charging power supply, and the voltage on the cap........ before you let the cap run the JT.

[TinselKoala]

@Bill.... yes, I think changing the value of the base resistance does change the frequency somewhat, but what you are describing.... which I have seen many times too, usually just before blowing a transistor or a load LED  ..... might be attributed to overdriving the transistor into and beyond full saturation. Back off from this point..(after putting in a new transistor!!) and you get back to your "sweet spot" where you are switching the transistor cleanly and it makes the best waveform for amplification in the transformer coils.
Try this sometime: When your 2n2222 JT is running along nicely, cool off the transistor with the liquid from an inverted spraycan of "air duster" stuff. You know what I mean... if you just barely press the button while the can is upside down you get the cold liquid to come out in dribbles. Dribble this onto the 2n2222 and watch what happens when the transistor gets really cold. It will usually shut off. Don't change the base resistance while it's cold, or you might get a surprise when it warms back up.

@MH: if the JT circuit isn't in "resonance".... what determines the oscillation frequency?

How are we defining resonance here, anyway?

ETA: If the JT coil set is considered to be a transformer, then you could determine its resonant frequency in the usual way: drive one coil with a FG, sweep frequencies, look for voltage peak on the output. Then put the coil into a JT circuit, compare its running freq with the resonant freq you determined by sweeping. Then see what happens when you change one or the other, by adding caps to the JT, varying its base current, or by adding or removing turns from coils, to get them to match...... if you can, or need to. I haven't tried this, so consider it a testable hypothesis at this point. And another evening of playing around with recycled parts, for me, I guess.



ETA2: I agree with both of you actually, because I think you are both right. The normal operation of the JT is determined as MH says. But it's undeniable that operating at the correct frequency for the transformer's natural resonance is going to give you the greatest voltage rise on the output. And if you go even further and prevent core saturation by using non-saturable air or vacuum,  and use a quarter-wave resonator for your secondary .... you will have invented the Tesla Coil !!