Is joule thief circuit gets overunity?

[Void]

btw,what kind of voltages does one get on a average bakspike?

It varies widely depending on many factors such as the exact driving pulse shape, duty cycle, frequency, amplitude, inductance of the inductor, current drive capability of the pulse source, etc. The voltage amplitude of the generated back spike will also depend on any load that is connected to the inductor and the diode type used to capture the spike, etc. Any load connected can potentially greatly limit the amplitude of the back spike. Many factors involved.

[profitis]

@void yes caps r tricky due to fluctuating voltage/countervoltage,heat,leaks etc thats why i recomend bats,80percent efficiency conversion electro energy to chemical energy and vise versa.you take your now series charged load bats and swap in parallell to use as a source,throw away the single original(now flat) source and replace with same number of flat bats as the original load and from there it can be perpetual swaps,series to parallel,parallel to series,assuming overunity.

[Void]

Something interesting. I haven't had a whole lot of time for testing in the last few weeks, but I conducted a few tests this morning with my proto-board joule thief circuit. This is very preliminary, and some further analysis would be required to try to determine what exactly is going on, but this is what I measured. I ran this test twice to try to eliminate inadvertent measurement error as a factor in the results. Ran tests on my JT circuit to compare circuit efficiency when powering the circuit with a regulated DC power supply set to 0.5VDC, as compared to powering the circuit with my 3000 Farad nominal value super capacitor charged to about 0.5VDC. My measured results in both test runs using the 2 channel scope data logging/instantaneous power/average power calculation method for input and output power, show the super cap powered JT circuit as giving about 6% to 7% or so increase in circuit efficiency. Input and output currents are a bit less when powering with the super cap, so that might account for the increased efficiency, but I am not sure. I would need to run more tests to see if this apparent increase in circuit efficiency is consistent over a number of test runs. This same sort of test could probably be run to compare a regulated DC power supply to an AA or AAA cell as well.

[TinselKoala]

It's hard to know just how much the supply's regulation and filtering is affecting your measurements, though. Certainly you aren't going to be able to "recharge" your power supply from the JT circuit, as some people think happens with batteries! At low voltages, most bench supplies aren't going to perform as stably or cleanly as they do at higher voltages. There are ways to get around this by using external voltage dividers and heavy filtering, probably, but not many experimenters are likely to go to that much trouble to assure clean and precise low-voltage power.

Some experimenters have even been known to cite the power supply's own display meters, usually digital, for their voltage and current measurements. I kid you not.

[profitis]

@void,perhaps your regulated dc source is pulsing?if its from the mains.