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Author Topic: Magnetic fields within a toroid inductor.  (Read 77174 times)

Offline MileHigh

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Re: Magnetic fields within a toroid inductor.
« Reply #90 on: September 18, 2013, 01:00:27 AM »
Xee2:

Quote
Yes. When the sum of the fields is zero, both fields are still present. Just because the net field strength at some point is zero, it does not mean that there is no magnetic field at that point. It only means you can not detect the field at that point. The fields do not magically disappear, they are still there. I see many text books saying that the magnetic field "disappears" and that is not true.

If the net field strength is zero, then there is no magnetic field at that point.  Look at the case of the two wires example, one with current flowing downwards and the other with current flowing upwards.  There will be zero net field when the magnetic field vector due to each wire is equal in strength and they are 180 degrees apart in direction.

A little complication that may be worth mentioning is that when you walk around the loop and do the summation you are only looking at the part of the magnetic field that's in the same direction that you are moving.  Look at the original clip where he says something like "the dot product can be ignored because the direction of integration and the direction of the magnetic field are always in the same direction."   He intentionally keeps it simple where the magnetic field is always in the same direction as the movement.

What this means is that in the two-wire example you can have net zero field in the direction of your tangential movement which contributes zero to your summation, but there still could be a "radial" magnetic field.  You don't worry about the possible "radial" component of the net magnetic field due to the two wires.  You travel in your circle and add up the magnetic field components that are in the same (or 180 degree opposite) direction that you are traveling.  I may have made things too complicated, so I don't know if I am helping or hindering.

Quote
You lost me there. The distance to any particular wire will change as you move (unless you move in a circle around it).

I think I may be able to explain this one without complicating things too much.  Let's suppose the toroid has 360 turns.  You are standing on your circle outside the toroid and you are going to take your walk around the loop.  The circle you are going to walk on is centered on the center of the toroid and the toroid has perfect symmetry.

So you are looking at the toroid.  Then you move one degree along your circular path to the right.  What do you see?  You see the toroid and it looks exactly the same.  You move ten degrees along the path and you look at the toroid, it still looks exactly the same.  The distance between you and each wire of the toroid that cuts the center plane is always the same when you look at the wires as a whole set.  So if the toroid looks exactly the same from any angle, then the magnetic field MUST be the same at any point along the circle.  If you do the same thing on a circle with a larger radius, the same type of thing happens.

So you know that the magnetic field must always be the same as you go around the circular path because of symmetry.  You also know that the summation of your magnetic field times your movement must be zero amperes.  Certainly your movement in meters is not zero, therefore the magnetic field strength must be zero everywhere outside the toroid for everything to make sense and add up properly.

So that also means if just one loop of the toroid is larger than all the others and sticks out, then the symmetry is broken and now there will be an observable magnetic field everywhere outside the toroid.  That's why you say that a real-life toroid that you make on your bench will have a "near zero" magnetic field outside the doughnut shape, because it's impossible to build a toroid with perfect symmetry.

MileHigh

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Re: Magnetic fields within a toroid inductor.
« Reply #90 on: September 18, 2013, 01:00:27 AM »

Offline MileHigh

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Re: Magnetic fields within a toroid inductor.
« Reply #91 on: September 18, 2013, 01:37:28 AM »
Tinman:

Quote
I think i may have found a time lag in the magnetic field,from the outer part of the core,to the inner part of the core-or something like that???
Ok,we have a toroid core with three windings of equal length and wire size raped around the toroid core.1 is our primary,and the other two are the secondaries.Each secondary has a 100 ohm load resistor across it. Using an ac input to the primary,is it possable to get a phase shift between the two secondaries? from 0* right through to 180* out,simply by raising the frequency?.

A component like a transformer will only work properly below a certain frequency.  So it's not surprising that you see the phase shift change as you increase the frequency.  However, there should be a certain bandwidth where the transformer does its job properly.  The phase shift could be due to capacitive and other effects.  If you Google something like "AC characteristics of a transformer" or "frequency response of a transformer" you should get tons of hits.

As a side note and not related to this discussion, the classic mechanical equivalent for a transformer is simply a set of two gears.  If you look at the rotational speed and torque characteristics of a set of gears they are identical to the voltages and currents associated with an electrical transformer.

MileHigh

Offline xee2

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Re: Magnetic fields within a toroid inductor.
« Reply #92 on: September 18, 2013, 02:29:18 AM »

If the net field strength is zero, then there is no magnetic field at that point. 


I greatly respect your opinions, but I do disagree with you on this (and I know many agree with your position, so I may be the odd man out).
If you have a space filled with multiple magnetic field generators, as you move about the space there may be places where the magnetic field strength goes to zero. If the magnetic fields actually disappeared, then where did the energy in the magnetic field go? The only reasonable answer, is that the fields and their energy are always there. It is only measured strength that goes to zero. Back when I started in electronic engineering (a long time ago) we used slot lines (which are slots cut in wave guide) with a probe to measure the e-field strength inside the wave guide as a way of determining microwave frequency. If the signal really disappeared when the e-field went to zero there would be no wave coming out the end of the wave guide (but there was). I feel that teaching that the field disappears creates a lot of confusion about what is really happening.

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Re: Magnetic fields within a toroid inductor.
« Reply #92 on: September 18, 2013, 02:29:18 AM »
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Offline tinman

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Re: Magnetic fields within a toroid inductor.
« Reply #93 on: September 18, 2013, 02:32:59 AM »
Well at these high frequencies,probably nothing out of the ordinary then, But here is the experiment anyway.
First i cast two half toriod cores ,using liquid steel. Perm not so god,but still quite magnetic. I then wound one of the secondaries around one half of the toroid core. I then glued the two halves together. So now we have the secondaries windings passing through the middle of the core.

Once dry,i then wound the primary and the second secondairy around the whole core-as per normal.All wires were of equal length. It's a bit rough,but was only for a quick experiment.
Sorry the volume is a bit low,but it was filmed at 1am,and everyone was asleep.

http://www.youtube.com/watch?v=_C1VC_-f3Z0

Offline xee2

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Re: Magnetic fields within a toroid inductor.
« Reply #94 on: September 18, 2013, 03:02:13 AM »

So that also means if just one loop of the toroid is larger than all the others and sticks out, then the symmetry is broken and now there will be an observable magnetic field everywhere outside the toroid.  That's why you say that a real-life toroid that you make on your bench will have a "near zero" magnetic field outside the doughnut shape, because it's impossible to build a toroid with perfect symmetry.

MileHigh
Nice explanation.  :)

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Re: Magnetic fields within a toroid inductor.
« Reply #94 on: September 18, 2013, 03:02:13 AM »
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Offline xee2

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Re: Magnetic fields within a toroid inductor.
« Reply #95 on: September 18, 2013, 03:43:51 AM »
TinMan,
The coil around half of the core has less wire than the coil around the entire core, thus there is more capacitance between the windings in the coil around the entire core. This capacitance creates a parallel resonant circuit with the coil inductance. As the coil goes through self resonance the voltage across it increases. As the frequency goes beyond resonance the reactance goes from inductive to capacitive which is what produces the phase shift. You should be able to see the self resonance of each coil by increasing the frequency until the voltage peaks. In your video it looks like the blue coil peaks at a lower frequency than the other coil. This gives some more information about self resonance >> http://www.cliftonlaboratories.com/self-resonant_frequency_of_inductors.htm






Offline tinman

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Re: Magnetic fields within a toroid inductor.
« Reply #96 on: September 18, 2013, 05:19:10 AM »
Hi xee2
The three coils are of tha same length of wire.The coil wound around the half core has more turns that the two around the whole core-but the lengths are the same,as i cut all three lengths side by side befor i wound them.
It wasnt to show anything speacial,just sharing an experiment i did to see what would happen.

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Re: Magnetic fields within a toroid inductor.
« Reply #96 on: September 18, 2013, 05:19:10 AM »
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Offline xee2

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Re: Magnetic fields within a toroid inductor.
« Reply #97 on: September 18, 2013, 07:15:35 AM »
Hi xee2
The three coils are of tha same length of wire.The coil wound around the half core has more turns that the two around the whole core-but the lengths are the same,as i cut all three lengths side by side befor i wound them.
It wasnt to show anything speacial,just sharing an experiment i did to see what would happen.
Then it may be that the capacitance of both coils is the same. But the inductance of the coils is most likely different. However, if you look at the charts in the link I referenced, you can see how the phase changes as the frequency goes through the self resonance of the coil. I think this is the phase change you are seeing.

Offline Magluvin

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Re: Magnetic fields within a toroid inductor.
« Reply #98 on: September 18, 2013, 08:35:22 AM »
Just got finished with my lasersaber motor. Still working on my dual reed switch holder, but have made a single to mess with in the mean time. May get out a vid tomorrow. 

Should have my linear hall sensors this week hopefully to do some tests on a wound toroid.  I want to test one that is wound all the way around and one that has a primary on one portion and a secondary on the other.  I can imagine that if there are fields in the hole of the toroid, if wound all the way around, fields, or say flux will be coming from all the turns at the same time from all angles. So it may read neutral in the center, but more the closer to the inner windings. But, if I wind primary to the left and sec to the right, and still get a neutral enter, I should get a difference from left to right and up and down from center. At least these are my ideas on testing this and anticipated outcomes, possibly.

But one of the reasons Im even writing this is some thoughts I had on other test. Lets say we have 2 toroid cores and wind them the same. Then use a ferrite rod through the toroids centers like an axle with wheels. I wonder if input to one would induce the other? Just thinking. If we can run 1 wire through the toroid, equal to 1/4 turn, really, and get output from that wire, then why not see if we can draw out any flexing fields from one core to another via an axle core.  Also, how would a core in the hole of a toroid affect the toroid coil function, or value. All things to try.

Tinman. Nice idea on the home made split core with windings inside the core. ;)   I have thought of that before but never tried. I have seen parametric transformers that seem similarly buried in the core in relation the other winding.

So the buried coil has less output compared to the outer secondary. ??? ;D Well, only half the length of its inner windings, being they turn into the core half way, are available for induction in the hole as compared to the other secondaries inner portions of its winding as they go all the way around.  Even though there are more turns on that other secondary, Im sure it is not double the outer turns, and the difference in output is not half either. So it may be that you are showing some possible proof of what I was saying about all the action is in the open area of a toroid.  :o ;D Maybe not. But it sure does fit the ideas possibilities.

Now, what would really kick off some brain cells is to cut the kids toy 90deg from where you cut the first mold for your core so that you have an outer diameter part and an inner diameter part. lol, just thinking of this as I write and I need to get to bed, but... 

Now, when you cast your parts, if there is a way to create a gap, so the parts could fit with windings through the gap, then, wind a coil on the outer diameter part, then wind the inner diameter part then apply more JB weld or what ever mix your using to glue it together, Then wind a primary over that.

What will be interesting is which secondary, the inner or the outer will have what output. It would be funny if the inner had more, especially considerably more. ;)

Nite

Mags

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Re: Magnetic fields within a toroid inductor.
« Reply #98 on: September 18, 2013, 08:35:22 AM »
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Offline Magluvin

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Re: Magnetic fields within a toroid inductor.
« Reply #99 on: September 19, 2013, 12:15:01 AM »
Hey Tin

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

Dave45

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Re: Magnetic fields within a toroid inductor.
« Reply #100 on: September 19, 2013, 03:17:46 AM »
Lets say we have 2 toroid cores and wind them the same. Then use a ferrite rod through the toroids centers like an axle with wheels. I wonder if input to one would induce the other? Just thinking. If we can run 1 wire through the toroid, equal to 1/4 turn, really, and get output from that wire, then why not see if we can draw out any flexing fields from one core to another via an axle core.  Also, how would a core in the hole of a toroid affect the toroid coil function, or value. All things to try.

Mags

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Re: Magnetic fields within a toroid inductor.
« Reply #100 on: September 19, 2013, 03:17:46 AM »
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Offline MileHigh

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Re: Magnetic fields within a toroid inductor.
« Reply #101 on: September 19, 2013, 04:25:37 AM »
Xee2:

Quote
If you have a space filled with multiple magnetic field generators, as you move about the space there may be places where the magnetic field strength goes to zero. If the magnetic fields actually disappeared, then where did the energy in the magnetic field go? The only reasonable answer, is that the fields and their energy are always there. It is only measured strength that goes to zero. Back when I started in electronic engineering (a long time ago) we used slot lines (which are slots cut in wave guide) with a probe to measure the e-field strength inside the wave guide as a way of determining microwave frequency. If the signal really disappeared when the e-field went to zero there would be no wave coming out the end of the wave guide (but there was). I feel that teaching that the field disappears creates a lot of confusion about what is really happening.

You are missing an important distinction.  We were talking about an example were there were interacting fields from two wires with DC current going through them.  In that case there will be places in the 3D field where there is no magnetic field and by definition there is no electric field.

Here is a thought experiment:  You have a 10-meter length of straight wire.  So that's an inductor.  You put 10 volts across the ends of the wire and let's say 10 amps of current flow.  It takes a short while to overcome the inductance and build up the magnetic field that surrounds the wire.  So we know that there is a certain amount of energy stored in the magnetic field around the wire.

Now, lets take the same same wire and make a 180-degree bend at the 5-meter point so that the wire is folded over and the two ends of the wire are right next to each other.  You put 10 volts across the terminals and 10 amps of current flow.  However, there is a huge difference here.  The parallel halves of the wire create magnetic fields that mostly cancel each other out.  Therefore the inductance for this wire configuration is much much smaller than for the straight wire.  Therefore the current rises to 10 amps much much faster, and there is much much less energy stored in the magnetic field around the wire.  So there is no "energy that was always there" in this configuration.  There is simply less energy from the get-go.  Everything balances out like it is supposed to.

In your case, you are making reference to standing waves in a microwave waveguide cavity.  I vaguely remember doing the experiment where you stick a sensor needle into the slit in the waveguide to sense for the intensity of the electric field.  I am not qualified to state exactly what is going on there but I can say that this is an AC resonator-type configuration and not a DC configuration.  So it's a whole different ball of wax and when you aren't sensing the electric field there may be a complimentary magnetic field at play.  I get a headache just thinking about it.

Let's look at a more manageable AC standing wave setup.  You set up standing waves with a skipping rope.  So is there no energy at the nodes where rope is not moving?  The answer is no, when the skipping rope standing wave reaches the peak of the oscillation and stops for a brief second, all of the energy is stored in the stretched rope.  So the non-moving node is actually the center of a stretched linear spring in this example.  You have a rough analogy were the AC rope velocity and the AC rope stretched spring tension are equivalent to the AC electric field and the AC magnetic field.

It's a good segway into thinking about an analogy for an energized inductor.  I think many people on the forums might just think that "it happens."  Think of holding a big beryllium copper torsion bar in between your two hands.  You twist it and takes a lot of work to bend it.  You can only hold it in the bent position for 10 seconds max.  So you release the pressure and it kicks back.  There is your "collapsing magnetic field."  If you are straining to hold it in the twisted position, it may feel like your body is doing work on the bar, but of course that's not the case.  You hold it for as long as you can and then the work you put in will be kicked back at you.  People on the forums often fail to visualize the work aspect to energize a coil and the fact that the magnetic field is kind of "stressing" the space in the immediate area and the space wants to stress right back and get back to normal.  You are "bending the space" and it doesn't like it and wants to get back to the unbent position.  Instead, they daydream about the clockwork of the Universe, or they search for "magical" coil configurations, bla bla bla.  It's much more basic than that.

MileHigh

Dave45

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Re: Magnetic fields within a toroid inductor.
« Reply #102 on: September 19, 2013, 05:23:23 AM »
Quote
You are missing an important distinction.  We were talking about an example were there were interacting fields from two wires with DC current going through them.  In that case there will be places in the 3D field where there is no magnetic field and by definition there is no electric field.
Not true, you dont know what you are talking about, period.
I could prove you wrong but will not waste my time.

Offline MileHigh

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Re: Magnetic fields within a toroid inductor.
« Reply #103 on: September 19, 2013, 05:38:05 AM »
Dave45:

Quote
Not true, you dont know what you are talking about, period.
I could prove you wrong but will not waste my time.

I do know what I am talking about.  There is an electric field but in the context of this example there is no electric field that merits being part of the discussion.  Also, the dismissive "waste my time" shtick is getting tiring and it's rude.  Likewise, saying "you don't know what you are talking about" is just a cop out on your part.  I have been around this forum long enough so that many people will state that I do know what I am talking about and I try to make a point of only discussing what I know about.  By the same token I am human and not perfect.

So, like I said before, make your case and be straight with no hints, no teases, no smoke and mirrors.  Please stop making these "spooky" postings.  Just be real.  Can you do that?

For reference, here is the example from the earlier posting:  We were talking about an example were there were interacting fields from two wires with DC current going through them.  In that case there will be places in the 3D field where there is no magnetic field and by definition there is no electric field.

Where is the electric field in this example Dave?  Please state your proof that I am wrong.

Dave45

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Re: Magnetic fields within a toroid inductor.
« Reply #104 on: September 19, 2013, 06:21:43 AM »
Your right it was rude and I apologize
Here's some more pseudoscience for ya

this is a coil powered with 12v dc
 

 

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