Is joule thief circuit gets overunity?

[ltseung888]

Day 5 (Mother's Day) at 3:30pm.  LED on Board 116 is still ON.

@void

I can see that you are using the breadboard.  I stopped using the breadboard because the results from different breadboards by different individuals were very different.  In particular, we tried to place the hand over the board and the scope shots changed significantly.

For a fair comparison, please give me your snake mail address and I can send you two Zhou boards FREE.  The passing test for the Zhou board is "crossing the 0 ref line" on the Atten. 

The simplest test with the Zhou board at present is - just use a rechargeable AA battery as Input and hook up to Vin+ and Iout-.  (previous boards use A1+ and A4-)   Use a DMM to measure the voltage (also connected across Vin+ and Iout-).  The Voltage will drop from 1.4V to 0.4 volt in 2-3 days.  Then at around 0.4V, strange things start to happen.   The expectation is that it will die (LED OFF) within hours.

The experimental result will show that the LED will be ON dimly for at least 2 or more days.  The Input waveform will have spikes as shown.  Not all JT circuits will show such characteristics.  Only the Zhou Boards are "guaranteed to have such characteristics because if a board does not pass this test, it is NOT a Zhou Board.....

Welcome to this lead-0out energy research.  TK. PW and Poynt99 will teach you on how to use your DSO.  Each DSO is different and thus every one goes on a different learning curve.  The good thing at present is - I do not even need a DSO to show that a rechargeable AA battery reading 0.352V can light up the LED for days dimly (Board 116).  If I add a capacitor and a timer, a similar AA battery reading 1.317V at beginning can light up a similar LED brightly for a much longer time.

*** Poynt99 taught me three years ago NEVER to use the Vrms value for analysis.  The correct way is to use Instantaneous Power = Instantaneous Voltage x Instantaneous Current.

The experiment is still on-going.  More independent teams are welcome.  You can be one of them.....

[ltseung888]

I tried another test with the exact same Joule Thief circuit that I used in my previous test (see me previous post above), except this time I placed a capacitor in parallel to the 1k ohm base resistor. I didn't have all that many capacitor values in the low nF range to try with, but I tried 100nF, 20nF, and 10nF. The 10nF nominal value (12.5nF measured value) capacitor seemed to give the highest efficiency of these three values. With the 12.5nF capacitor in parallel to the 1k ohm base resistor, efficiency increased to 95.2%, however the LED glows dimmer for about the same input voltage due to less current flowing in the circuit. At any rate, adding a parallel capacitor across the 1k ohm base resistor appears to have increased efficiency a fair bit with my circuit setup. Thanks Tinselkoala for the suggestion. If you compare the scope shots from the previous test to the scope shots from this new test, it appears that the parallel base capacitor limits the amplitude of the current spike peaks quite a bit, which for some reason seems to increase efficiency a fair bit. This also caused the frequency of oscillation to increase a fair bit as well. I am attaching the scope shots which I used to make the input and output measurements with the 12.5nF cap across the base resistor.

Average Input Power:
Vin = 510mV
Iin = 1.84mA
Input Power = 938uW

Average Output Power:
Vout = 921mV
Iout = 970uA
Output Power = 893uW

Efficiency = 893uW/938uW x 100 = 95.2%

- void -

In the scope shots below, yellow are the voltage traces, and green are the current traces.

@Void,

Please do what TK asks - include the resistors and probe connections in your circuit diagram.  Poynt99 has clearly explained that the current values should be negative for DSO analysis.  Your shots showed positive.  Did you use the Invert function?  If not, your shots may be measuring something totally different.  Please check.

[Void]

@TinselKoala, @Lawrence:
A quick reply for the moment.
I am attaching a schematic which includes the placement of the two 1 ohm current sense resistors I used, as well as the scope probe leads placement I used to make my measurements.

Regarding my using the RMS measurement feature on my scope to make my voltage and current measurements for these tests, as I mentioned I am aware that using the RMS feature (equivalent to what a True RMS voltage meter does, I believe) is not the most accurate way to make measurements for input and output power with these types of waveforms. There are certainly limitations there, and I am aware of this.

From what I have observed, my scope appears to only use the positive portion of a waveform to do the RMS calculations (I am not certain of this, but the scope appears to do it this way), so if you have an AC waveform in which the positive and negative swings of the waveform are not really close to being symmetrical, then using the RMS feature is not going to give very accurate results at all. However, in my measurements here I observed that the waveforms were all pulsating DC (i.e. no negative swings to the waveforms for the most part) so I think my using RMS measurements here should give at least ballpark results. I agree that using this measurement technique for these type of waveforms is potentially not very accurate, so I would definitely want to confirm the measurements using a better measurement method before attempting to draw any definite conclusions. These tests I did so far were just preliminary to get an approximate idea of the efficiency of the circuit. I plan to do more careful measurements later.

I am quite familiar with the use of oscilloscopes, but my experience is fairly old school with basic analog scopes, so I will have to familiarize myself with using some of the other capabilities my DSO has, such as data logging and math and calculation features.
@TinselKoala, I will check what other calculation/math features my DSO has.
@Lawrence, I would like to take you up on your offer to run tests/measurements on your joule thief board. I will email you later today with my mailing address. Thank you.
@Lawrence, since I am using a 2 channel DSO and I measure the input and output power separately by moving the scope probes over, I can connect in my scope probes as shown in the attached schematic when measuring the input voltage and current, and there is no need to invert the current channel when attaching the scope probes this way, I believe. At any rate I was using RMS values to calculate the average input power, so if the input waveform was inverted it shouldn't matter when using the RMS value for the current (my waveform was pulsating DC). For instantaneous power measurements, I agree that it is important to make sure that no waveforms are inverted.

Thanks for the feedback guys!

- void -

[ltseung888]

@TinselKoala, @Lawrence:
A quick reply for the moment.
I am attaching a schematic which includes the placement of the two 1 ohm current sense resistors I used, as well as the scope probe leads placement I used to make my measurements.
*** Try to use the same circuit as mine.  My circuit will cater for both 2-CH and 4-Ch scopes.  It will also be a closer comparison.

Regarding my using the RMS measurement feature on my scope to make my voltage and current measurements for these tests, as I mentioned I am aware that using the RMS feature (equivalent to what a True RMS voltage meter does, I believe) is not the most accurate way to make measurements for input and output power with these types of waveforms. There are certainly limitations there, and I am aware of this.
*** Poynt99 will probably repeat his explanation once more or point you to the past posts. 


From what I have observed, my scope appears to only use the positive portion of a waveform to do the RMS calculations (I am not certain of this, but the scope appears to do it this way), so if you have an AC waveform in which the positive and negative swings of the waveform are not really close to being symmetrical, then using the RMS feature is not going to give very accurate results at all. However, in my measurements here I observed that the waveforms were all pulsating DC (i.e. no negative swings to the waveforms for the most part) so I think my using RMS measurements here should give at least ballpark results. I agree that using this measurement technique for these type of waveforms is potentially not very accurate, so I would definitely want to confirm the measurements using a better measurement method before attempting to draw any definite conclusions. These tests I did so far were just preliminary to get an approximate idea of the efficiency of the circuit. I plan to do more careful measurements later.

I am quite familiar with the use of oscilloscopes, but my experience is fairly old school with basic analog scopes, so I will have to familiarize myself with using some of the other capabilities my DSO has, such as data logging and math and calculation features.
*** Make sure that you are 100% efficient and confident on the EXCEL analysis of the captured results.  The captured results will reproduce the displayed waveforms and much more.

@TinselKoala, I will check what other calculation/math features my DSO has.
@Lawrence, I would like to take you up on your offer to run tests/measurements on your joule thief board. I will email you later today with my mailing address. Thank you.
@Lawrence, since I am using a 2 channel DSO and I measure the input and output power separately by moving the scope probes over, I can connect in my scope probes as shown in the attached schematic when measuring the input voltage and current, and there is no need to invert the current channel when attaching the scope probes this way, I believe. At any rate I was using RMS values to calculate the average input power, so if the input waveform was inverted it shouldn't matter when using the RMS value for the current (my waveform was pulsating DC). For instantaneous power measurements, I agree that it is important to make sure that no waveforms are inverted.
*** Please continue your experiments with the Board you built.  I shall send you Board 118 and Board 119.  The test result for these two boards will be posted here first with all test details.  Please pay special attention to the test results of these two boards.  Raise any questions or doubts.  Once you receive them, you can repeat the tests and compare them with your own boards.

Thanks for the feedback guys!

- void -

[ltseung888]

Day 6 results on Board 116.  LED still ON dimly.

LED on Board 124 still ON brightly (but not as bright as beginning of Day 1).