Talk:Eddy current

message: Hello to all concerned. I have the most basic of knowledge concerning magnetic fields, so I am having a little trouble interpreting the picture. More experienced persons may find my lack of comprehension amusing, but I can assure them that I have a better chance at understanding the picture than the average wikipedia user. It is for this reason that I suggest that someone may find it worthwhile to at least include what I,V and B represent. Thanks. 138.64.2.77 (talk) 16:10, 21 August 2008 (UTC)
thread_title:  Picture 

message: I do not believe the supplied equations are correct. The units for f were unclear, and when I performed dimensional analysis I found that f2 would have to have the units of kg m-1 s-2. This is clearly erroneous. 
Eshansen (talk) 23:59, 24 November 2009 (UTC)
replies: text: I concur. It wasn't the units of f that I was concerned about, it was the definition of D.  What could the density of the material have to do with eddy current loss?  I think that D in this case is Dpen, the penetration or skin depth.  Skin depth has a major influence on eddy current losses, was missing from the formula, and has the correct dimension so the units on left and right side match.  Henkdeleeuw (talk) 05:54, 23 February 2010 (UTC)
replies: text: Units still don't add up in the current article. When I check T^2*m^2*Hz^2/(Ohm*m*m) I get kg/(s^3*m^2), but power is kg*m^2/s^3. So there's a missing length^4. That's way off. The only thing I can think of is that it's using flux density (T) instead of flux (Wb). That's a difference of m^4, and it makes sense. My resources on induction heating all refer to flux rather than flux density when calculating power. V = -N(dFlux/dt) and P=V^2/R so (Flux*frequency)^2/R would have the right units. --W0lfie (talk) 14:51, 9 August 2010 (UTC)
thread_title:  Strength of Eddy Currents 

message: Faraday's law of induction#Eddy currents has some nice text and illustrations related to eddy currents and mitigation. Maybe something could be copied here. --Steve (talk) 12:38, 29 July 2012 (UTC)
thread_title:  content that could be copied here 

message: This comment concerns the statement in this article "Eddy currents in conductors of non-zero resistivity generate heat..." and whether a citation is needed for that claim.
First, I would like to address whether the claim is true (which is not the same as the question of whether in belongs in a Wikipedia article; see WP:V).
There are two aspects to this. First, according to Ohm's Law, zero ohms equals zero watts equals zero heat generated.  This is well-cited in Superconductivity. The converse and equally true statement is that any current in a conductor of non-zero resistivity generates heat. Alas. both Power and Electrical power are rather light on citations, so we can't just Wikilink to them. 
Second, there is the question of whether eddy currents occur in a superconductor. Our article starts out by saying "Eddy currents (also called Foucault currents) are electric currents induced within conductors by a changing magnetic field in the conductor." An obvious corollary is this: no magnetic field = no induction = no eddy current.  
It is a well-known property of superconductors that they are perfect magnetic shields (up to a point; a strong enough field will cause them to cease to superconduct). Sort of like Mu-metal on steroids. Perfect magnetic shielding = no magnetic field = no induction = no eddy current. Well known, but as I found out when I was designing such a shield for electron microscopes, the "perfect" isn't exactly perfect in real life. It does come close, and the nature of the imperfect magnetic shielding really doesn't affect eddy currents - see below for details. 
The mechanism behind the lack of magnetic field in a superconductor is the Meissner effect, which expels all magnetic fields. Well, almost. This is actually only true once you get past the London penetration depth (a couple of hundred nanometers).  Can we get an eddy current within the London penetration depth? I have no idea whether this is possible.
A lot of EEs get this wrong, because applying Faraday's law of induction with resistance equal to zero in the calculations gives a similar answer -- no change in magnetic flux -- but Faraday's law doesn't quite explain what happens when you have a magnetic field before the conductor-to-superconductor transition.
Another issue is that a perfect Meissner effect is difficult to
achieve in practice. As the material undergoes the superconducting transition, small amounts of flux can be trapped in the metal, "pinned" there by tiny non-superconducting impurities.
When I was working on the electron microscope shield, we experimented with using eddy currents to reduce this trapped flux. It turns out that tin has a huge drop in electrical resistivity just before it becomes superconducting. So if you rapidly rotate a tin cylinder while cooling it through the transition region, any outside magnetic field induces eddy currents in the low-resistance-but-not-yet-superconducting tin. These eddy currents tend to drive out magnetic flux before the the tin becomes superconducting and thus able to trap the flux. Alas, the effect doesn't work for the axial component of the external field, and it doesn't survive a warmup/cooldown cycle in the field.
the question is, how much of the above needs to be in the Eddy Current article and how much needs to be backed up with citations. Is "Eddy currents in conductors of non-zero resistivity generate heat..." likely to be challenged? If so, is a Wikilink to Superconductivity good enough, or do we need citations for all of this in this article? --Guy Macon (talk) 16:00, 4 October 2012 (UTC)
thread_title:  "Eddy currents in conductors of non-zero resistivity generate heat..." 

message: User:Embrittled has started edit warring in order to push his preferred version over the objections of at least two other editors. I have placed a warning on Embrittled's talk page and encourage him to dicuss the reasons for his changes here. Wikipedia:BOLD, revert, discuss cycle (often shortened to WP:BRD) has some excellent advice about this. --Guy Macon (talk) 01:39, 31 October 2012 (UTC)
replies: text: I'd like to point out that Guy Macon is, in effect, involved in the edit warring himself, and is making personal attacks on this page, and is pushing his own personal views on Wikipedia as well; as well as misrepresenting the situation here. There are actually reliable sources that support my edits, as well as material that is produced by universities and many other sober websites as well.Embrittled (talk) 03:07, 31 October 2012 (UTC)
replies: text: A single revert is not edit warring. Please read WP:3RR. And please give us citations to those reliable sources; if the sources support your version, then of course i support it as well. --Guy Macon (talk) 07:12, 31 October 2012 (UTC)

text: So you think that if you revert somebody else multiple times that's not battlegrounding, nor is it if you are posting lots of your insulting tags across numerous talk pages, nor is tagging your subject lines with multiple insulting tags.Embrittled (talk) 21:34, 31 October 2012 (UTC)
replies: text: Again, please read WP:3RR and WP:BATTLEGROUND. Reverting you on Oct 1 and then again on Oct 31 after you ignored four editors urging you to discuss your edits on the article talk page is not unreasonable. Your repeated violations of WP:CIVIL and WP:NPA are. The path you are on will lead to you being blocked from editing Wikipedia. If you stop it now and instead follow WP:CONSENSUS your desired changes will be evaluated fairly. --Guy Macon (talk) 03:11, 1 November 2012 (UTC)
thread_title:  Edit warring by [[user:Embrittled]] 

message: I've recently seen some bicycle light generators that use eddy currents from magnets placed next to alloy rims. 
How would efficiency compare to a dynamo hub or a friction-driven bottle generator? --Triskele Jim 01:29, 19 January 2016 (UTC)
thread_title:  Power generation 

message: Substituted at 14:07, 29 April 2016 (UTC)
thread_title: Assessment comment

message: You need a section on eddy current motors.  — Preceding unsigned comment added by Arydberg (talk • contribs) 23:49, 1 July 2016 (UTC)
thread_title:  eddy current motor 

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thread_title:  External links modified 

message: In the Explanation section, I think we should clarify that the Lorentz force on the electrons carrying the eddy currents is what opposes the conductor's motion in the brake diagram, rather than the opposing B-field in the perpendicular axis. The moving charges closer to the magnet feel more force, and that force is in the same direction (-v) on both ends of the magnet. We need to show that net force vector antiparallel to v. Seems like explaining it by just saying that the eddy currents induce an opposing B-field is hand-waving and misleading.
For example: https://opentextbc.ca/physicstestbook2/chapter/eddy-currents-and-magnetic-damping/  — Preceding unsigned comment added by 173.127.151.28 (talk) 10:58, 13 April 2020 (UTC)
replies: text: Thanks! I wrote that section of the article. I can't believe I missed that.  I corrected the text.  --ChetvornoTALK 20:26, 23 October 2020 (UTC)
thread_title:  Ultimate source of drag force