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Author Topic: Is joule thief circuit gets overunity?  (Read 600437 times)

poynt99

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Re: Is joule thief circuit gets overunity?
« Reply #900 on: May 20, 2013, 04:23:14 PM »
Regarding the apparent negative or zero-crossing current trace, sorry Lawrence I do not trust your scope.

I won't believe the current trace crosses the zero-reference line until I see it on a higher-end scope. Why can you not borrow an Instek scope from Mr. Zhou?

Void

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Re: Is joule thief circuit gets overunity?
« Reply #901 on: May 20, 2013, 06:29:23 PM »
Try to analyze the strange Board 113.
Board 113 was the strange board withwaveform totally different from other Boards.  Previously, I just treat such Boards as reject.  Now on TK's advice, I keep them and try to analyze them.
Just show the strange waveforms first.  The first comparison of Board and connections appeared correct.
*** It looks like the best thing for me to do is to keep the Board.  Wait until I find the right person to debug.  I do not have the energy, skill and equipment to do a proper job.

Hi Lawrence. Feel free to send this board to me for testing if you like. I can confirm if it is doing anything unusual or not. 

Void

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Re: Is joule thief circuit gets overunity?
« Reply #902 on: May 21, 2013, 01:17:02 AM »
I used the data logging feature of my scope to log the data points for the input and output voltage and current waveforms for my 'standard' joule thief circuit, and then used Excel to crunch the numbers to calculate the instantaneous power values and to calculate the overall average power. If anyone sees any errors or problems with the  measurement/calculation method, or with the way I set up the formulas in Excel, let me know. 

I connected the scope probes as shown in the attached schematic. Connecting the probes this way at the input does not invert the input current waveform, to make things simpler. Since I am using a 2 channel scope and just moving the scope probes over between input and output measurements, this probe connection method should be fine. If using a 4 channel scope to measure both input and output waveforms all at once, then you could use the probe connection method that Lawrence has been using, but the input current waveform will be inverted. You would not be able to use my scope probe connection method if connecting all four probes from a four channel scope at the same time to the circuit. 

Vin was set to about 504mV.

Here are the calculated values:
Pin = 2.954mW
Pout = 2.034mW
Efficiency = 68.86%

See the attached .xls files for the actual recorded data points and details of the calculations.

In the attached scope screen shots, the yellow traces are the voltage waveforms, and the blue traces are the current waveforms.
« Last Edit: May 21, 2013, 05:36:56 AM by Void »

TinselKoala

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Re: Is joule thief circuit gets overunity?
« Reply #903 on: May 21, 2013, 03:29:37 AM »
Re 113: more likely to be a "damaged" transistor than wrong toroid connections. There are 4 possible ways to wire the toroid into the circuit, I think two will work and two won't work at all, and of the two that work sometimes one works slightly better but the frequency should be pretty much the same for both working hookups.
I have a special 2n2222 here that is partially failed; it acts somewhat like the 113 board, if I recall correctly. Or the transistor might even be a different type. Did you check the markings?

One thing is certain: two of your resistors are in backwards.

TinselKoala

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Re: Is joule thief circuit gets overunity?
« Reply #904 on: May 21, 2013, 03:35:31 AM »
@Void: One problem with the way that you are doing it, with one scope, is that you are comparing a set of input power measurements taken at one time, and for a certain duration, with another set of output power measurements taken at a different time. Hopefully you have at least equated the number of full cycles, which is probably more appropriate than equating number of samples, but I don't really know which would be best.
I've suggested this alternative for those with a single scope: take input and output _current_ at one session, then take input and output _voltage_ at the other session. At least that way you will be taking the input and output readings simultaneously (or nearly so, separated by the scope's sample interval).

Void

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Re: Is joule thief circuit gets overunity?
« Reply #905 on: May 21, 2013, 04:06:30 AM »
@Void: One problem with the way that you are doing it, with one scope, is that you are comparing a set of input power measurements taken at one time, and for a certain duration, with another set of output power measurements taken at a different time. Hopefully you have at least equated the number of full cycles, which is probably more appropriate than equating number of samples, but I don't really know which would be best.
I've suggested this alternative for those with a single scope: take input and output _current_ at one session, then take input and output _voltage_ at the other session. At least that way you will be taking the input and output readings simultaneously (or nearly so, separated by the scope's sample interval).

@tinselkoala: I understand what you are referring to in regards to the number of cycles. The time base is the same for both input and output measurements, so the number of cycles should be the same, but the triggering point may not be exactly the same since the current waveforms are different between the input and output waveforms, and I am triggering on the current waveforms for both measurement steps. Average power calculation for both input and output waveforms is done for the exact same amount of data samples (20,480 samples), so I would think that this should still average out about the same, but it is possible that there could be some degree of discrepancy due to different trigger points between input and output measurements. Not sure that your proposed alternate method would resolve that potential discrepancy of different trigger points, since in one measurement step I would be triggering on current, and in the other measurement step I would be triggering on voltage.

Using a two channel scope to do these measurements is no doubt a bit of a compromise. I guess it is just a question of how much potential there is for error using this method, due to different trigger points.

Edit: Was just thinking about this some more, and I don't know if my scope synchronizes the data logging with the trigger set point, so the trigger point setting may not make much difference as far as synchronization of input and output measurement start points. Maybe the data logging does sync off the trigger set point though. I suppose I could run some tests to see if the data logging always starts at about the same point in a waveform for the same trigger setting...


 

ltseung888

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Re: Is joule thief circuit gets overunity?
« Reply #906 on: May 21, 2013, 05:46:37 AM »
Re 113: more likely to be a "damaged" transistor than wrong toroid connections. There are 4 possible ways to wire the toroid into the circuit, I think two will work and two won't work at all, and of the two that work sometimes one works slightly better but the frequency should be pretty much the same for both working hookups.
I have a special 2n2222 here that is partially failed; it acts somewhat like the 113 board, if I recall correctly. Or the transistor might even be a different type. Did you check the markings?

One thing is certain: two of your resistors are in backwards
.

Markings are the same 2n2222.  I shall send it to Void.

Void

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Re: Is joule thief circuit gets overunity?
« Reply #907 on: May 21, 2013, 02:54:34 PM »
Try to analyze the strange Board 113.
Board 113 was the strange board withwaveform totally different from other Boards.  Previously, I just treat such Boards as reject.  Now on TK's advice, I keep them and try to analyze them.
Just show the strange waveforms first.  The first comparison of Board and connections appeared correct.

Hi Lawrence. What were you using to power board 113 when you did those tests that you posted the waveforms for? DC power supply, super cap, or AA battery?

ltseung888

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Re: Is joule thief circuit gets overunity?
« Reply #908 on: May 21, 2013, 04:22:59 PM »
Hi Lawrence. What were you using to power board 113 when you did those tests that you posted the waveforms for? DC power supply, super cap, or AA battery?
For Board 113, I used DC Power Supply.

Void

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Re: Is joule thief circuit gets overunity?
« Reply #909 on: May 21, 2013, 04:52:14 PM »
For Board 113, I used DC Power Supply.

Ok, thanks.

ltseung888

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Re: Is joule thief circuit gets overunity?
« Reply #910 on: May 22, 2013, 04:32:32 AM »
@Void,
 
I shall be sending you the items in the diagram.  They fit nicely into the plastic box.  Please review and see if you need anything else.  I shall also post the test results for all the Boards here first and outline what I believe to be the "confirmation" experiments.  You are welcome to do any additional tests.
 
Two spare boards 133 and 134 will be included.  You can pass them on to whomever you feel as helpful.
 
God Bless.

ltseung888

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Re: Is joule thief circuit gets overunity?
« Reply #911 on: May 22, 2013, 10:18:17 AM »
The presentation file in pdf format.
 
I shall for comments before sending out the Boards.

ltseung888

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Re: Is joule thief circuit gets overunity?
« Reply #912 on: May 22, 2013, 10:19:58 AM »
DSO Analysis for Board 118.  COP = 1.37.

ltseung888

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Re: Is joule thief circuit gets overunity?
« Reply #913 on: May 22, 2013, 10:21:52 AM »
DSO Analysis for Board 119.  COP = 1.73.

ltseung888

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Re: Is joule thief circuit gets overunity?
« Reply #914 on: May 22, 2013, 01:53:18 PM »
DSO analysis for Board 118 when the LED was just lighted up.  Note the large COP =  5.27. 
 
For this test, the Probes and Scope set to x1.  Since the Atten is only 2-CH, the output and Input measurement were separated by a few minutes.  At this low voltage (and blinking LED light?), the readings cannot be trusted.  With blinking light, high degree of error or fluctuation was expected.
 
May need the 4-CH Tektronics to resolve this issue.