PhysicsProf Steven E. Jones circuit shows 8x overunity ?

[gyulasun]

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It is interesting that the measured inductance L values are different also,
Single wound, L = 10 uH (@100 Hz), 1.9 uH (@ 10 KHz)
Bifilar wound,  L = 11 uH (@100 Hz), 2.4 uH (@ 10 KHz)
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Hi Steven,

Would like to suggest a a couple of things to make your B field measurements more precise.

First I suggest to use a simple self adhesive tape for fixing the winding ends onto the nails because as I could make out from your pictures on the setup the windings can spring out (spread out lengthwise), this may explain the small difference in the L inductance at 100Hz between the single and bifilar coils. The higher difference in L at 10kHz may involve also the effect of the loose winding ends, together with some nonlinear permeability change at such a frequency for a nail iron material (normally very bad cores above some hundred Hz, with increasing eddy losses too).

Second I suggest to place the B field probe to the head end of the nails where the facing areas are more defined, comparing this to the needle end of the nails where you actually placed the probe (more uncertainty can creep in).  You could touch the probe straight onto the head, facing the probe to it. This way the mV values would be higher too due to the bigger surface area of the head ends.

Maybe shifting the position of the single coil on the surface of the nails before fixing it with a tape and finding the same L value the bifilar coil has at 10kHz could help making the two coils more uniform, this would bring more meaningful B field measurements. (Not that your data so far is less meaningful of course, the factor of 2 difference in the B field is surely close to reality.)

Regarding the self capacitance measured values of 104uF or 122uF is meaningless for me (I think this is an artifact of the meter)  unless the meter showed a transformed value of the normally expected some pF parallel self C into the equivalent higher series value at 10kHz. Could you study the User manual of the meter, maybe it includes some hints on coils self capacitance measurement. 
Normally a coil's  self C is measured by connecting two different known C values in parallel with it, one after the other and measure the two different resonance frequencies, then calculate self C from the Thomson formula.
http://www.qsl.net/in3otd/inductors.html 
Here is another tip:
http://forum.allaboutcircuits.com/showthread.php?t=8660  but this involves using a grid-dip meter (a frequency calibrated variable oscillator) for learning on the coil's self resonance frequency.

Thanks,  Gyula

EDIT  PS: MAybe my suggestion of bringing the two coils self inductance equal at 10kHz (by shifting the single coil axially on the nail) sounds absurd (due to the DC current excitation when tested in series).  In case you can nicely fix the number of turns tightly on the nails for both of the coils with tape and then find the 100Hz inductance measurement match better than before for the 10 and 11uH results, then the 10kHz "fine tuning" is not needed of course.

[xee2]

Single wound, L = 10 uH (@100 Hz), 1.9 uH (@ 10 KHz)
Bifilar wound,  L = 11 uH (@100 Hz), 2.4 uH (@ 10 KHz)

Thanks for taking the measurements. I think this answers your original question as to why bifilar picks up more - it has 10% more inductance. Since the magnetic field strength is related to inductance, the bifilar has a stronger magnetic field and thus picks up more.

[JouleSeeker]

Thanks for taking the measurements. I think this answers your original question as to why bifilar picks up more - it has 10% more inductance. Since the magnetic field strength is related to inductance, the bifilar has a stronger magnetic field and thus picks up more.

The next question is -- why does the bifilar-wound coil have greater L than the single-wound coil?  both have a total of 30 turns...

@Gyula:
Thanks,  Gyula

EDIT  PS: MAybe my suggestion of bringing the two coils self inductance equal at 10kHz (by shifting the single coil axially on the nail) sounds absurd (due to the DC current excitation when tested in series).  In case you can nicely fix the number of turns tightly on the nails for both of the coils with tape and then find the 100Hz inductance measurement match better than before for the 10 and 11uH results, then the 10kHz "fine tuning" is not needed of course.

I will try that experiment, good idea (when I get back up to the University).
Thanks. 
Steve

[nul-points]

Steven

there's a new arrangement being reported on the 'Joule Thief' thread where the circuit is run from two batteries in series and two similar batteries are placed in parallel to receive some re-charge at the connection between the supply and the oscillator - the parallel batteries can receive charge both from the supply and from the coil-field collapse current, fed back thro' a diode or LED

the initial idea is to run the circuit for some time, then swap the charging batteries to become the new supply and make the previous supply batteries receive a charge - over time the graph of the battery voltages will show if the batteries are charging/self-sustaining/discharging

i've made a new inverted looped variant of your SJ1 circuit to include this feature and i'm now including it with my other ongoing logging of SJ1 variants - i'm using 2 pairs of AAA NiMHs for this experiment

thanks
np


http://docsfreelunch.blogspot.com

[Hope]

I think I know this one!  Magnetic fields at 90 degree angles to each other pass thru each other without interfering with each others flux.  (Lots of each others sorry). So magnetic fields have phasing, would this mean other fields have polarization to?  Whats your understanding on this effect Steve?
How can we apply this to our builds to an advantage?