Investigating "anomalies" in Bifilar coils

[Chet]

Here some Odd behaviors of the bifilar coil will be investigated .

underconstruction

[CITFTA]

Typo in subject
"Bifiler" should be "Bifilar"

Is that an anomaly? LOL   

I wonder why for some of us that word is so hard to type correctly.  I find myself about half the time typing it with an "e" when I know it is supposed to be an "a".  Sometimes I catch myself and sometimes it is a day or so later before I see what I have done.  The human mind is a strange thing.

[Chet]

well
I have a hard time reading and typing since the last eye surgery[last week] , and I'm a terrible speller anyway !!

Here some discussions will evolve around experiments which have shown anomalous behavior [or is it ?]

will take a few hours to get this sorted so it has a sense of direction, some of Partzman's earlier observations
will be discussed as well as wireless behavior and magnetic behavior of Bifilar coils ,and not just round coils.

[TinselKoala]

Well, as long as you aren't a terrible smeller, it should be OK !


Meanwhile, back at the ranch....


One Tesla Bifilar (TBF) flat coil as "primary" being fed with sinewave signal (Blue) from ElCheepo DDS FG at 10V p-p, through a 9.4 ohm precision noninductive resistor with a scope probe across the resistor (Yellow). One monofilar coil with same amount of wire and turns as "secondary" mounted co-axially about 1 cm away from "primary", used as sense coil, directly connected to scope probe (Purple).  One scope shot at 5 seconds/division horizontally, while FG scans across frequency range. (Two full 30 second scans shown.)  Another scope shot at the resonant frequency of the TBF coil. Both shots show that the voltage across the current-viewing resistor "flatlines" at the TBF coil's resonant frequency, which should mean that there is no current flowing. Right? Yet the voltage trace from the "secondary" monofilar pickup coil shows clearly that there is voltage induced in that coil. So there must still be a substantial alternating magnetic field happening in the TBF coil. Right?

[Verpies]

What is the ground lead of the blue probe connected to ?

So there must still be a substantial alternating magnetic field happening in the TBF coil.

...or alternating electric field.

[TinselKoala]

The "Blue" probe is a direct connection from the second channel of the DDS FG to the oscilloscope with a BNC patch cord. The first channel of the FG is connected by the red and black clips in the photo. While this FG has isolated "ground" the isolation is broken by making the connection to the scope with the BNC patch cord. So all channels of scope and FG share the same ground.

It's hard for me to see how either the magnetic or electric fields can be alternating so nicely when there is no current -- or more precisely voltage drop -- evident in the CVR. Unfortunately when the "secondary" pickup coil is loaded with, say, an LED, the TBF's CVR current trace no longer flatlines. It gets small and still is at minimum at the TBF's resonant frequency, but is definitely no longer at zero.

(I know the colors are actually cyan and magenta but on the live scope they look more blue and purple to me.)

[TinMan]

It's hard for me to see how either the magnetic or electric fields can be alternating so nicely when there is no current -- or more precisely voltage drop -- evident in the CVR. Unfortunately when the "secondary" pickup coil is loaded with, say, an LED, the TBF's CVR current trace no longer flatlines. It gets small and still is at minimum at the TBF's resonant frequency, but is definitely no longer at zero.

Wonder if the coil is heating up,while there is no current flowing through it?


Brad

[partzman]

TK,

If you would measure the inductance of just one of the bifilar windings in your TBP and also the capacitance between the windings, I would attempt a sim to see if the TBP is functioning as a cross coupled symmetrical transmission line as depicted in the attached schematic.

Regards,

PM

Edit: Added "cross coupled".

[TinselKoala]

TK,

If you would measure the inductance of just one of the bifilar windings in your TBP and also the capacitance between the windings, I would attempt a sim to see if the TBP is functioning as a cross coupled symmetrical transmission line as depicted in the attached schematic.

Regards,

PM

Edit: Added "cross coupled".

OK, so I disconnected the centertap and measured the two windings individually. They measured 176 uH and 172 uH. Capacitance between windings is 2.80 nF (but we know this isn't the distributed capacitance when the centertap is connected). When centertap is reconnected the total inductance measured 680 uH. The DC resistance is 3.90 ohms.

[partzman]

OK, so I disconnected the centertap and measured the two windings individually. They measured 176 uH and 172 uH. Capacitance between windings is 2.80 nF (but we know this isn't the distributed capacitance when the centertap is connected). When centertap is reconnected the total inductance measured 680 uH. The DC resistance is 3.90 ohms.

OK, thanks for the info TK.  The overall distributed capacitance will take of itself when the L's and C's are lumped and I will probably use 12 sections for reasonable accuracy.  What is interesting from your inductance measurements is that there is apparently very little coupling between the windings based on the ratio of the series connection to an individual winding or 680/174(avg) = 3.90 with 4.0 being no coupling at all.  This makes it much easier to do the sim.  If you see a problem with this, let me know.

Regards,
PM

[partzman]

TK,

Here is a sim of your TBP modeled as a symmetrical 12 section transmission line with the parameters you supplied.  There are no parasitics included nor couplings between sections so the accuracy may reflect this when comparing these results to your bench tests.

TBP_1A shows the plot sweep from ~50kHz to 1.25MHz and as can be seen there are 2 dips and 1 peak in Vout across the 1 ohm sense resistor.  There is also a trace showing the sum of the all the currents in the odd inductors L1-L23 over time representing one winding of the TBP and the other line is identical but not shown for clarity.  Also, the 10v peak input voltage Vin from the generator is divided by 100 for plot clarity.

TBP_2A shows an expanded view of the first dip in output voltage/current in Vout across/thru R1.  The frequency is ~277kHz, Vout is ~561uv rms, while the total current in the odd L's is ~140ma rms.  This shows the apparent output current to ground of the TBP to be nearly zero while there is still induction in both windings which would be detectable with a separate sense coil in proximity.

TBP_3A shows an expanded view of the 1st peak in output current at 505kHz plus the levels of output voltage and the odd L's winding current.

Based on your measurements,  your TBP has a Td=1.38us and Z=492 ohms.

Regards,
PM

   

[JimBoot]

there's a vicious rumour going around that someone is onto a sweet deal with a pancake coil supplier. Without mentioning any names <cough>Partzman</cough> Can anyone get in on that action?

[TinselKoala]

TK,

Here is a sim of your TBP modeled as a symmetrical 12 section transmission line with the parameters you supplied.  There are no parasitics included nor couplings between sections so the accuracy may reflect this when comparing these results to your bench tests.

TBP_1A shows the plot sweep from ~50kHz to 1.25MHz and as can be seen there are 2 dips and 1 peak in Vout across the 1 ohm sense resistor.  There is also a trace showing the sum of the all the currents in the odd inductors L1-L23 over time representing one winding of the TBP and the other line is identical but not shown for clarity.  Also, the 10v peak input voltage Vin from the generator is divided by 100 for plot clarity.

TBP_2A shows an expanded view of the first dip in output voltage/current in Vout across/thru R1.  The frequency is ~277kHz, Vout is ~561uv rms, while the total current in the odd L's is ~140ma rms.  This shows the apparent output current to ground of the TBP to be nearly zero while there is still induction in both windings which would be detectable with a separate sense coil in proximity.

TBP_3A shows an expanded view of the 1st peak in output current at 505kHz plus the levels of output voltage and the odd L's winding current.

Based on your measurements,  your TBP has a Td=1.38us and Z=492 ohms.

Regards,
PM

   

Verry interesting indeed. IIRC I measured 273.2 kHz for the resonant frequency of this coil, so your sim is not far off at all. Or rather, my measurement is not far off at all! Maybe even just my scope probe capacitance is enough to account for the 4 kHz difference.

[partzman]

there's a vicious rumour going around that someone is onto a sweet deal with a pancake coil supplier. Without mentioning any names <cough>Partzman</cough> Can anyone get in on that action?

Jim,

Yes, Chet and I had discussed the possibility if anyone was interested but you are the first to speak up.  I had ordered prototype boards from PCBWay in China as they are fast and quick with good quality and should still have the artwork on file but that is really not that important as I still have the files.  Several caveats however, the traces are rectangular with sharp corners by design plus the traces and plated thru pads are identical on both sides which means if one places them in a sandwich, you need to be creative when attaching to the inner layers and remove the appropriate plating in selected holes.  I do this by drilling and cutting as can be seen in the attached pix.  For this reason, I would recommend the artwork be changed if enough are interested.

I will have to dig in files to find the price for 10 pcbs plus the shipping plus I also have measurements of the pcb parameters in various arrangements which could be posted.

Regards,

PM   

[partzman]

Verry interesting indeed. IIRC I measured 273.2 kHz for the resonant frequency of this coil, so your sim is not far off at all. Or rather, my measurement is not far off at all! Maybe even just my scope probe capacitance is enough to account for the 4 kHz difference.

TK,

I am pleasantly surprised the two results are that close at ~1.5%!  Your scope probe capacitance and other bench parasitics plus the fact I didn't include any probably account for the difference.

PM 

[Chet]

PM
re an earlier discussion on Loose wire ,I was in error ...it was the spacing between the Windings which needed
"special attention"

whether or not Vibration plays a part ...as well as pulsing ?

[TinselKoala]

Dear Friends:
Magnetic field (AC) comparison rendering now and should be viewable in a couple of hours.   


Dear TinMan:
Saw your "BEMF" comparison; 100 percent Thumbs Up!   


Ever faithful, I remain
--TK 

[TinselKoala]

Magnetic field comparison video is up now. Sorry about the shaky camera, I couldn't use a tripod for this one, too many things to look at up close.

http://www.youtube.com/watch?v=sXKJjNAZDEM


And.... I was able to generate this beautiful textbook ringdown from one of my TBF coils, pulsed with a 9V battery. It takes some trial and error to get the momentary pulse just right using my fingers.

[TinselKoala]

... and the same sort of ringdown from the monofilar pancake coil. Pretty much identical except for the frequency, and slightly different noise on the beginning of the signal.

[TinMan]

Dear Friends:
Magnetic field (AC) comparison rendering now and should be viewable in a couple of hours.   


Dear TinMan:
Saw your "BEMF" comparison; 100 percent Thumbs Up!   


Ever faithful, I remain
--TK

Yes,BEMF is the same in the two coils.
Only difference so far,is as you have seen--the BPC has a lower self resonant frequency.

Brad

[Chet]

Ok
finally spoke with Stefan today about issue at OU.com

may take a day or so...
but all is good

also to note investigations here around BF coils will be focused much more in specific areas, not the least of which will be Partzman's MEI work

and of course once the mess at Stefan's is sorted... things can resume there

[TinMan]

T.K

I will be sending you a link to a video i am about to shoot-via PM.

This is in regards to something i have found with the BPC,that i have never seen in any other coil-and i have carried out this test with other coils.

We have been looking for something different about the BPC,and i think i may have just found it--never give up looking 

AFAIK,this go's against all the books tell us-AFAIK.

I have a theory as to why i am getting these result's,but we can discuss that after-after you confirm what i have found,to be correct.

Be in touch soon.


Brad

[TinselKoala]

T.K

I will be sending you a link to a video i am about to shoot-via PM.

This is in regards to something i have found with the BPC,that i have never seen in any other coil-and i have carried out this test with other coils.

We have been looking for something different about the BPC,and i think i may have just found it--never give up looking 

AFAIK,this go's against all the books tell us-AFAIK.

I have a theory as to why i am getting these result's,but we can discuss that after-after you confirm what i have found,to be correct.

Be in touch soon.


Brad

I can confirm that the effect you showed in the video is real, correct, and relatively easy to reproduce with my own TBFP coils. I also think I have an explanation, as I said in the PM I sent you. But I'll wait until you post your demonstration for everyone to see and discuss. I think Partzman will be especially interested and I am curious if he will hit upon the same explanation that I think I have. I also have a demonstration of what I think is another version of the same effect, in a different system that has been discussed here not too long ago. I'll try to get a video of this demo up, but I'll wait until after you've started discussing the effect in the open thread.
Cheers, mate--
--TK

[TinMan]

I can confirm that the effect you showed in the video is real, correct, and relatively easy to reproduce with my own TBFP coils. I also think I have an explanation, as I said in the PM I sent you. But I'll wait until you post your demonstration for everyone to see and discuss. I think Partzman will be especially interested and I am curious if he will hit upon the same explanation that I think I have. I also have a demonstration of what I think is another version of the same effect, in a different system that has been discussed here not too long ago. I'll try to get a video of this demo up, but I'll wait until after you've started discussing the effect in the open thread.
Cheers, mate--
--TK

just a quick stop in ,before hitting the road for another days work.
Thanks for doing the test TK.




Will get the video up tonight.


Cheers
Brad

[TinMan]

As a seco d test TK

If you get your BPC to once again show 0 current input-what do you get across !what would be! R2 in my video?

Brad