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Author Topic: Magnetic field outside a toroid with AC current...  (Read 14440 times)
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    Consider a toroid, that is a solenoid bent in the shape of a doughnut, wound tightly with wire.
Textbooks point out that with a DC current, the magnetic field B outside the toroid is ZERO.  For example, one can do a vector sum of B fields from individual wires, and these add to zero.  Or use Ampere's law to get the same result.

  Now apply an alternating current of high frequency to the wound-toroid.   Is the B field outside the toroid everywhere zero?  I think the answer is still yes (by Ampere's law).

  Next, add a loop of wire threaded through the center of the toroid and then circling around it, and put in a light bulb to form a complete loop (loop perpendicular to the plane of the toroid).  The light bulb lights up showing (AC) current in this external loop.  Yet all along the wire, the B field is zero.  So how do the electrons in the external loop "know" that there is a changing flux down INSIDE the toroid?
   

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Even in the unlikely case where the B field is totally contained, the act of containing that B field creates the A field (magnetic vector potential) along the axis of symmetry. The changing and contained B field is the source for the changing A field.

The primary current (through your first poloidal direction windings - most will call these 'toroidal windings' and still be correct.) creates a changing E field in the same plane as the A field but reverse direction. This changing E field is what induces current in your secondary poloidal direction winding. Or as I would normally put it - The changing E field drags current from the secondary wire.

In spite of virtually all theory showing a magnetic field as a separate entity, toroidal transformer theory quite clearly shows that this isn't the case. All magnetic fields (defined variations in magnetic density) are just that - variations of magnetic density within a pervasive magnetic flux.
The compressed presence of like polarized magnetic domains in a permanent magnet simply compress the already existing ambient flux.

Here is a fairly good explanation which avoids my esoteric view ..   http://en.wikipedia.org/wiki/Toroidal_inductors_and_transformers



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"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   
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Hi Steve
No ,i dont think the field is contained within the core.The reason being, that i and many others have made pulse motors using toriod's as run coil's. If the field was contained within the core,how dose the rotor spin?.There has to be a magnetic field pushing against the rotor magnet's.
   

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tinman,

By your description I wonder if you were alternating between rotor magnet to toroid core attraction and no attraction.

The reason is you can block magnetic attraction to a toroid core by saturating the core with the toroid's winding current.

I don't know how correct this is but the concept can be found in numerous texts and provided some clarity, for me.

The H field is also known as the magnetizing field (plus the standard definition). It cannot exist in the same strength when not in attraction/repulsion to the object to be magnetized.
The B field is also known as the magnetized field (plus the standard definition). It cannot exist at all without the H field.

So, if the toroidal core is already magnetized to the full extent possible there is nothing for another field to attract to or repulse from.

All becomes confusing unless you finally use Maxwell's correction to Ampere's law.


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"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   
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You could well be right WW, in regards to the pulse motor setup's.
So i put together this little video,using low power high frequency AC into the toroid.Now the core is a ferrite magnet from a speaker,so this may well have something to do with the outcome-but i don't believe so,as the coupling looks pretty close-other than the phase shift due to the high frequency.
http://www.youtube.com/watch?v=WNOtEDkCSpA
   
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The magnetic vector potential (A), although a mathematical construct, can be more useful than the magnetic field density (B) for certain problems. 

Magnetic induction can occur in a zero curl magnetic vector potential field, as the toroid illustrates.  The only requirement is a time changing field.

EM
   

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It's not as complicated as it may seem...
Brad,

With regards to your video, the induction in your pickup coil is the result of a changing magnetic field. The changing magnetic field is the result of driving the toroid coil, which partially re-polarizes the magnetic domains in your speaker magnet.

With no input current, the axis of the majority of the speaker magnet domains is in the vertical plane. When you apply some current to the coil, some or all of the magnet's domains will rotate towards the horizontal plane, and the degree to which they rotate will depend on the current, strength of the magnet, and frequency of the drive signal.

If you were to replace the core with a non-magnetized material, or use no core at all, you should find that most of the B-field is contained within the toroid, and you will have little to no signal in your pickup coil.
   
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  Mags provided a PDF over at OU that I found instructive; when I asked the same question over there.
Not sure the author is correct, but he squarely addresses the question I was raising.

Attached is the document.
   
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Thank you for posting a most relevant and thought provoking document .
not many of us have the time to troll through the mass of  stuff over there .
   

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I suggest readers of Distinti's work consider that he may have repeatedly confused physical and coordinate effects.
Also, it does not appear he is aware that Maxwell already made corrections to Ampere's & Faraday's work.

What we generally attribute to many has already been modified by others.

It is a good idea to read original works and consider the exact context in which they were discovered.


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"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   
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Well this test isn't in regard to the field outside a toroid,but rather inside the toroid.
Sorry about the low volume,but it was 1am in the morning when i shot the video,so i had to be quiet lol.
The video explains how i wound the toroid,but basically i have one of the secondary windings going through the center of the toroid core.
http://www.youtube.com/watch?v=_C1VC_-f3Z0
   
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Well this test isn't in regard to the field outside a toroid,but rather inside the toroid.
Sorry about the low volume,but it was 1am in the morning when i shot the video,so i had to be quiet lol.
The video explains how i wound the toroid,but basically i have one of the secondary windings going through the center of the toroid core.
http://www.youtube.com/watch?v=_C1VC_-f3Z0

Wow!  I really enjoyed this vid, Tinman.  Now why would you think that the phase and amplitude would shift like that?  180 out of phase and higher output from the half-toroid-wound coil...  Why?  sure seems weird.  Rather sharp "resonance behavior" as well!  Cool stuff.  

(And why are there 8 likes and 3 dis-likes?  can't imagine  why the dislikes... pls ignore those)

Where else are you posting about this, may I ask?
And what "path" are you following here -- is this McFreey related?
Thanks again.
« Last Edit: 2013-09-18, 15:16:22 by PhysicsProf »
   
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  I'm thinking... when you get 180 deg out of phase like that, can you do an end run around Lenz?  wishful thinking probably...
   
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@ Steve
McFreey related?

I do have it posted on my forum,but it wasn't going to be ongoing,just a test trying something different.I posted it at OU as well,but it seems that it is just the different capacitance between the two secondary winding's??.There is something interesting with it but.If i short the secondary that is wound around the full core,the other secondary drops in output.But if i short the secondary that is wound around half the core,there is no effect on input power ,or the other secondaries output?.

I'll do a bit more testing on it,but then i want to build another toroid,but have it halved vertically insted of horizontally.I will then wind one secondary on the inner half,and the other on the outer half-and carry out some test on that.
This was something Mag's said i should try,so i'll give it a try.
   
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  OK, looking forward to your further results.
Note thread I was talking about:  http://www.overunityresearch.com/index.php?topic=1526.0   , but probably not related upon further reflection.
Thanks again.
   
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Mmm-well that thread looked like it was going well,then just stoped?.
   
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Mmm-well that thread looked like it was going well,then just stoped?.
Hey Tin
If you havnt wound the cores yet, wait till I get home to describe a more definitve  way to do so. Bout 3 hours ill be off work. Glad your trying it. :)
Mags
   
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Hey Brad

Below is an illustration of how I think it should be wound as to isolate the windings from each other to eliminate winding to winding proximity and to let the core do its thing.  If we wind primary directly over the secondaries, the secondaries will surely get induced by the primary directly as the flux from the primary is attracted to the core, cutting the secondaries along the way. This might not show us exactly what we are looking for, which is how the primary flux engages the secondary using the core as the path from the primary to secondary. Also having 2 secondaries wound on top of one another may affect the outcome because they share the area in between the cores.  So isolating them from each other should give more definitive results as to what is going on with the core being the only connection(magnetically) between windings.  Then fill in the gaps in the 2 cores with your liquid core material. Hope that makes sense.  ;D

Also, no need for many windings. I would do 10 turns for each and just 1 tight layer each. Just use a current limiting resistor, non inductive, in series with the primary to accommodate signal gen capabilities.  Results should be as good as many turns without all the work.  My soundstream amp uses 3 turns of 6 parallel wires for a primary and it works great. And thats at 60khz. But play with the freq all you want. :D
Mags
   
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  I'm thinking... when you get 180 deg out of phase like that, can you do an end run around Lenz?  wishful thinking probably...

Interesting thought. ;)  If one sec is out of phase, how would that affect the loading of the primary as compared to the normal phase sec? :D  Good catch there. ;) ;D
I suppose comparison is easy, just load 1 sec at a time and compare with both loaded. It would be interesting to watch the primary also with these tests.  O0

Mags
   

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There will be a slight phase shift between the primary and other windings (beyond 180 degrees) but it has more to do with the operating characteristics of the core than the position of the primary in relationship to other windings.

AAMOF, you should expect that there is almost no difference between a secondary wound over the primary vs. wound directly on the core somewhere else.(the proximity between a primary and a secondary wound on top of the primary will cause differences but these should be minor and not due to position on the core.) Distini's ideas are very flawed on how a toroidal transformer works until you operate it near the top of the core's frequency range.


---------------------------
"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   

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  I'm thinking... when you get 180 deg out of phase like that, can you do an end run around Lenz?  wishful thinking probably...

I would think if Lenz wasn't involved there would be no output on the secondary  ???


---------------------------
"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   
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Whats interesting to note,is that my scope has a common ground,wich means that the two secondary coils are actualy hooked in series.So we have series conected coils ,sharing the same core,with the ability to shif the phase of the two series coneced inductors out from each other.
Wonder what the output would look like with just one trace across the two secondaries conected in series ?.
   

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 :)

They would only be in series if you closed a circuit with a load between the ends that are not common with each other. If you simply connected those uncommon ends together the coils would then be in parallel. Since they don't feed the same load - having a common ground should mean nothing.

You should have a math function on your scope. Subtract one channel from the other. You should see what would happen if you connected the windings in parallel potential-opposing.


---------------------------
"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   
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