Jump to content

Talk:Toroidal inductors and transformers

Page contents not supported in other languages.
From Wikipedia, the free encyclopedia

This is an old revision of this page, as edited by 208.127.16.197 (talk) at 12:55, 20 December 2012 (→‎Misleading Illustrations, Inaccessible References, Confounding Explanations). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

formula needed

This page ought to have formulae for calculating inductance of toroidal transformers. I have an air-core, toroidal transformer for which i want to know the inductance. The given external link, ostensibly a toroidal calculator, is no help; and since it is also littered with ads, i'm thinking it is too spammy to place on wikipedia. -- 99.233.186.4 (talk) 00:54, 16 September 2010 (UTC)[reply]

Proposing to delete the Sentence "The magnetic flux in a toroid is largely confined to the core, preventing its energy from being absorbed by nearby objects ..."

Energy does readily get out of a toroidal inductor into nearby objects. For example, the nearby object may be the secondary coil of a toroidal transformer. And it is a good thing because if energy could not get out of a toroidal inductor then a toroidal transformer would not work, because the primary is a toroidal inductor. But, there is a grain of truth in this sentence. It is easier to shield a toroid than some other shapes. A lot of the benefit comes from having a closed magnetic path. It is the axial symmetry (taking the axis to be the line through the center of the donut hole) and a restriction that the current does not have a "toroidal" component that leads to the conclusion that the "lines of flux" are axial circles of constant intensity. Combine that with Faraday's law and one can compute that the B field is zero outside the core of the toroidal inductor. But it depends on having axial symmetry. If there is a chuck of magnetic material next to the winding, the symmetry is broken there is a non-zero B field outside the core of the toroid. As a didactic example, the toroidal coil is a poor example because it leaves the student thinking that he has mastered the idea when all he really did was learn a non-general special case.

I propose that the entire sentence be deleted. Constant314 (talk) 00:56, 7 October 2010 (UTC)[reply]

The flux is largely confined in a high μ toroid. I would not delete the statement, but a modification might be appropriate. There is a B field outside of the core; toroids have leakage inductance.
BTW, typical procedure is to put a dubious or disputed tag in the article statement that points to this section.
Glrx (talk) 04:31, 7 October 2010 (UTC)[reply]
Regarding your comment “dubious or disputed tag” would you kindly point me to a page that tells how and why to do that?
WP:AD, WP:dubious. Glrx (talk) 15:57, 8 October 2010 (UTC)[reply]
The flux is largely confined to the core if the core is made from a high &mu material and has a closed magnetic path, even if the material in no toroidally shaped. The ideal axially symmetric toroid sufficiently far from anything that would break the symmetry actually has zero external flux. And of course if it is far enough from everything, there is nothing to which couple energy. But the sentence as written is more wrong than it is right. Energy is not prevented from being absorbed by nearby objects. It is not self shielding; two toroidal inductors near each other have a significant non-zero mutual inductance. And it is only true that the flux “is largely confined to the core” in special cases where the axial symmetry has been preserved. So, if the choice comes down to having this sentence or deleting it, I think it is a better article without it. But, fixing it would be great. I think a statement like the following would be correct. “The toroidal form is somewhat easier shield than other forms. In some cases the form contains the magnetic field sufficiently enough to not need further shielding.” Constant314 (talk) 13:02, 8 October 2010 (UTC)[reply]
I disagree with your mod: consider a pot core. Shielding is about attenuating, and closed high μ mag path confinement does provide shielding. Glrx (talk) 16:12, 8 October 2010 (UTC)[reply]
I will take your suggestion and use the dubious method.Constant314 (talk) 06:52, 9 October 2010 (UTC)[reply]
It is interesting to note that the green torroids in the picture are not wound in a way to take advantage of B field confinement. Instead they act as a one loop coil in the plane to the toroid. Constant314 (talk) 16:31, 11 October 2010 (UTC)[reply]
I find your fix to agreeable. I am inspired to add a section about field confinement in a toroid. Constant314 (talk) 01:04, 19 October 2010 (UTC)[reply]
You are free to improve my fix; I don't think it is great. I'll look over the technical details of your field confinement edit. Your wonderful images may be appropriate for Rogowski coil -- where avoiding the residual winding is important. Glrx (talk) 03:06, 20 October 2010 (UTC)[reply]
if there is zero external flux, how does the Rogowski coil work? is that because the current generates a flux, which disturbs this property? i would welcome discussion of field confinement in the article, that includes cases when it does not apply -- 99.233.186.4 (talk) 03:21, 14 November 2010 (UTC)[reply]
Not sure about the Rogowski coil. I have a (stalled) work in progress on the torroidal transformer. The basic story is this: the B field is zero, but the A field (magnetic vector potential) is non-zero. The time derivative of A adds a component to the E field. The E energizes the secondary.Constant314 (talk) 04:46, 14 November 2010 (UTC)[reply]
There is a reciprocity theorem. If, in a certain circumstance, a particular current in the primary causes a particular open circuit voltage in the secondary, then the same current in the secondary causes the same open circuit voltage in the primary. In other words, the coupling inductance is the same no matter whether you drive the primary or the secondary. So, you can analyze the toroidal transformer with a one turn secondary you can infer the action of the Rogowski coil.Constant314 (talk) 15:40, 14 November 2010 (UTC)[reply]
The Rogowski coil does a closed contour integration -- summing the induced voltages around the loop. Then Green's theorem gives the flow rate of electrons through the loop's surface. Glrx (talk) 02:17, 15 November 2010 (UTC)[reply]
I had a quick look at some of the papers on the UK web site. My impression is that they are terminating the Rogowski coil with a low impedance so that it functions as a current transformer.Constant314 (talk) 10:31, 15 November 2010 (UTC)[reply]

More in-depth pictures

Pictures/Diagrams clearly showing primary and return winding terminus needed. As it is, it looks like the just dissapear. —Preceding unsigned comment added by 184.76.222.168 (talk) 02:43, 18 December 2010 (UTC)[reply]

which section?Constant314 (talk) 04:16, 18 December 2010 (UTC)[reply]

Better Article Needed

I doubt a lot of scientists come to Wiki for information on toroids. This should have a leading paragraph that states the information people want to know, which is WHY someone would want to use a toroidal transformer instead of a standard square unit. This article doesn't mention the word audio, or even radiation.--75.79.150.41 (talk) 07:10, 19 October 2011 (UTC)[reply]

We all look forward to your contribution to the article. cite it and write it!. --Wtshymanski (talk) 13:44, 19 October 2011 (UTC)[reply]
I think the article should tell what a toroidal inductor is before it tells why someone would want to use it. But telling why someone would want to use it surely belongs somewhere in the article. Constant314 (talk) 20:51, 19 October 2011 (UTC)[reply]

Original research

The field confinement and vector potential sections of this are absolutely correct, beautifully illustrated, and clearly explained. However, the only citations are in the initial paragraph or so, and so I suspect these are original research. I also think they put undue weight on these topics which, while mathematically and geometrically elegant, are not of much practical importance. Perhaps they can find a home other than Wikipedia. What do others think?Ccrrccrr (talk) 00:18, 23 October 2011 (UTC)[reply]

Add references and keep them! Add more about other topics if you think these have undue weight. Don't delete stuff. 71.167.58.122 (talk) 19:54, 21 November 2011 (UTC)[reply]

Lots of Useless Info.

This article s like an IBM manual; full of perfectly correct but entirely useless information. The basic equations are by Maxwell, and have been copied from an undergrad physics text book. Nothing to do with ferrite toroids, though. The word "saturation", highly pertinent for ferrites, is not mentioned anywhere.220.244.85.162 (talk) —Preceding undated comment added 01:55, 10 August 2012 (UTC)[reply]

The first sentence has links to transformer and inductor. They both discuss ferrrite. No need to duplicate that here. Constant314 (talk) 13:17, 10 August 2012 (UTC)[reply]

Misleading Illustrations, Inaccessible References, Confounding Explanations

Figures 5, 6, and 8 show an equal number of return wire turns to the primary winding in the opposite direction. Theoretically, that would neutralize (by shorting) all inductance. Further, the only references on this page are to books. Including internet references may enhance credibility. For example, http://www.cliftonlaboratories.com/toroid_and_solenoid_external_field.htm mentions the single turn effect. Finally, the sentence "No matter how many times the winding encircles the core and no matter how thin the wire, this toroidal inductor will function as a one coil loop in the plane of the toroid," implies the inductance is decreased without circumferential current compensation. Not the case. The afforementioned link better describes the "single turn effect."

The material may have merit but is badly presented. The presentation is so confusing that other users in ##electronics @ freenode IRC dismissed it as "free energy genius", and did not assist my understanding of it. — Preceding unsigned comment added by 76.104.2.80 (talk) 23:58, 10 September 2012 (UTC)[reply]

I can assure you that the inductors shown in figures 5, 6 and 8 do not have any shorted turns and function as normal inductors. As for your conclusion that the sentence "No matter how many times the winding encircles the core and no matter how thin the wire, this toroidal inductor will function as a one coil loop in the plane of the toroid," implies the inductance is decreased without circumferential current compensation, perhaps you can explain the reasoning that leads to your conclusion.Constant314 (talk) 04:17, 11 September 2012 (UTC)[reply]
As for the shorted turns, my mistake, sorry. Perhaps the article should clarify the return windings actually rotate the same direction as the primary, and therefore contribute a magnetic field in the same direction.
As for the wording of "No matter... one coil loop...", there are two distinct effects at work in toroids. As my reference states, "The typical toroid inductor can be considered to be two inductors. One is the traditional "circular solenoid" where the magnetic flux follows the core and the second is the one-turn loop..." Presently, the wiki article might be read to indicate both theoretical inductances are neutralized by lack of return winding. — Preceding unsigned comment added by 76.104.2.80 (talk) 16:19, 11 September 2012 (UTC)[reply]
I understand your point that the article may need clarification that the neutralizing winding only neutralizes the inductor in the plane of the torroid.Constant314 (talk) 00:14, 13 September 2012 (UTC)[reply]
I agree that the article has some flaws; my gripe is that it discusses theory as was mentioned above (textbook..) but says little about practical matters such as why it is used in certain applications. As was mentioned, Wikipedia serves a broad audience and tech and math theory doesn't serve much of that broad audience. I use ferrite toroids all the time and it's nice to know some theory (in layman's terms) but does that really add meat to what the typical reader is looking for when he hungers for knowledge about this? Even I'm not a typical reader so I think others should help answer that. Perhaps the article should be labeled as incomplete. What I would add is that toroids are found in many places that people don't even realize, such as on the ends of computer cables, as RFI/EMI suppressor sleeves. But they are often used in power supplies, CFL lights and communications equipment in the form of transformers that are sometimes hidden inside of a package. Why do designers use toroids instead of open core inductors such as bobbin cores? I'm not a designer so I can't add any insight to that. Signed by Watson 208.127.16.197 (talk) 12:55, 20 December 2012 (UTC)[reply]