Litz wire
in [Design]
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From: pimpom on 20 Feb 2010 13:52 Tim Wescott wrote: > On Sat, 20 Feb 2010 05:38:23 -0800, dcaster(a)krl.org wrote: > >> On Feb 20, 5:47 am, life imitates life >> <pastic...(a)thebarattheendoftheuniverse.org> wrote: >>> On Fri, 19 Feb 2010 16:58:13 -0600, Tim Wescott >>> <t...(a)seemywebsite.com> wrote: >>> >>> >>> >>>> On Fri, 19 Feb 2010 16:18:49 -0600, Tim Williams wrote: >>> >>>>> "George Herold" <ggher...(a)gmail.com> wrote in message >>>>> news:550831a9-5935-4e3d-b37e- > c664ebd9d752(a)o3g2000yqb.googlegroups.com... >>>>>> We get Litz wire from MWS but nothing that big. If you >>>>>> don't need >>>>>> that much have you thought of 'rolling your own'? >>> >>>>> I do sometimes, but only for small things. I'm >>>>> contemplating 10A >>>>> at 1MHz, so it needs to be pretty fine = way more strands >>>>> than >>>>> I'd want to deal with. >>> >>>>> I actually have some copper rope, which is about 1/4" >>>>> diameter and >>>>> looks to be made of 28AWG or so. I don't remember how many >>>>> strands >>>>> it is, but if I guess the rope is wound from 7 strands of >>>>> 31 >>>>> strand twist, that's 7*31 = 217. If 28AWG is good for >>>>> ~200mA, 217 >>>>> strands should be good for 40A, which sounds about right, >>>>> I'd >>>>> call it 8 or 10AWG equivalent. I salvaged this stuff from >>>>> some >>>>> old motor driver, which used a spool of this stuff for >>>>> air-core >>>>> inductors. >>> >>>>> Tim >>> >>>> Isn't there some magic braiding pattern for Litz wire? >>> >>> No. The wire strands have to be mag wire, which segregates >>> them >>> from >>> each other, allowing the skin effect to be taken advantage >>> of. >>> Without strand segregation, it becomes a single strand, from >>> the >>> POV of the current flowing in it, with only one skin for the >>> entire >>> mass. >> >> No again. The wire strands have to be segregated and also >> braided so >> that some of the time a strand is on the outside of the bundle >> and >> sometimes on the inside of the bundle. See attached from >> Wiki. >> >> Litz wire uses some different tricks. Instead of using one big >> conductor, it uses lots of little conductors (strands) in >> parallel >> (forming a bundle). Each little conductor is less than a >> skin-depth, >> so an individual strand does not suffer an appreciable skin >> effect >> loss. However, that is not the complete story. The strands >> must be >> insulated from each other -- otherwise all the wires in the >> bundle >> would short together, look like a single large wire, and still >> have >> skin effect problems. Furthermore, the strands cannot occupy >> the >> same radial position in the bundle: the electromagnetic >> effects that >> cause the skin effect would still disrupt conduction. The >> bundle is >> constructed so the individual strands are on the outside of >> the >> bundle (and see low resistance) for a time, but also reside in >> the >> interior of the bundle (where the EM field changes are the >> strongest >> and the resistance is higher). If each strand sees about the >> same >> average resistance, then each strand will contribute equally >> to the >> conduction of the entire cable. > > Why, then, does it work to make up multi-strand wire bundles > for SMPS > service where the wires are just lightly twisted into a bundle? > Are > these getting one part of the way there, but not all? > > I had heard about the Litz wire 'gotta be a magic braid > pattern', but > then I've seen all these SMPS transformers that just have > almost-parallel strands. One reason for using multi-strand wire even at mains frequency is that it utilizes winding space more efficiently than a single wire of the same cross-sectional area. Another reason is that multi-strand is easier to handle because of its greater flexibility. I've experienced both effects in practice. I can't speak authoritatively about the use of simple-bundled wire in SMPS transformers, but my guess is that it's a compromise of cost, availability and effectiveness. Individually insulated strands bundled in parallel should exhibit less skin effect than a large single wire, though perhaps not as effectively as specially braided true Litz wire. And at least some manufacturers are probably using it without investigating the effectiveness.
From: life imitates life on 20 Feb 2010 13:54 On Sat, 20 Feb 2010 07:33:54 -0600, "amdx" <amdx(a)knology.net> wrote: > >"life imitates life" <pasticcio(a)thebarattheendoftheuniverse.org> wrote in >message news:sauun5t4ct7i1ule9dj0lsihmjv5u5ecvs(a)4ax.com... >> On Fri, 19 Feb 2010 17:57:41 -0800, John Larkin >> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>>On Fri, 19 Feb 2010 13:21:36 -0600, "Tim Williams" >>><tmoranwms(a)charter.net> wrote: >>> >>>>Who sells this stuff (without paying for miles at a time)? >>>> >>>>I'm especially interested in stupid thick stuff, like, as large as 8AWG >>>>equivalent. Nebraska Surplus for instance doesn't stock wire like this. >>>> >>>>Tim > > >> Trial and error with gauges and strand count do >> more to optimize the result than ANY specialized, presumed to be required >> braiding or weaving. The segregation is the key to increasing surface >> area within a given cumulative "gauge". > > No need to do trial and error, Here's a table that gives recommended gauge >with regard to frequency. >See Table B. > http://www.litz-wire.com/technical.html >Same thing in pdf. >http://www.litz-wire.com/New%20PDFs/Frequency_Chart_3.01.13.09.pdf > >Regarding "ANY specialized, presumed to be required braiding or weaving": >This is used to equalize proximity effects which equalizes currents in the >individual wires. > >Quote from; http://www.dartmouth.edu/~sullivan/litzwire/skin.html >"The objective of twisting or weaving litz wire, as opposed to just grouping >fine conductors together, is to ensure that the strand currents are equal. >Simple twisted bunched-conductor wire can accomplish this adequately in >situations where proximity effect would be the only significant problem with >solid wire. Where skin effect would also be a problem, more complex litz >constructions can be used to ensure equal strand currents. Thus, in a >well-designed construction, strand currents are very close to equal." > > There is a great deal of information available about the use of litz wire, >if you have the math ability >you can become an expert in a couple of days! > Mike > Nice work there. Spot on. I wish the individual strand currents in these groups were all equalized. As it stands there are a bunch of dolts claiming to be on the ball, but obviously a bit kinked. You seem not to number among them most times I ever noted.
From: life imitates life on 20 Feb 2010 13:56 On Sat, 20 Feb 2010 05:38:23 -0800 (PST), "dcaster(a)krl.org" <dcaster(a)krl.org> wrote: >No again. The wire strands have to be segregated and also braided so >that some of the time a strand is on the outside of the bundle and >sometimes on the inside of the bundle. See attached from Wiki. It is indeed ideal, but not absolutely required. If you bundle does not conform to the pristine definition, it does not preclude it from exhibiting the effect, nor does it preclude you from calling it Litz wire.
From: life imitates life on 20 Feb 2010 13:58 On Sat, 20 Feb 2010 09:12:29 -0500, legg <legg(a)nospam.magma.ca> wrote: >Shake it loose and bake it to form an ~oxide layer on the individual >strands. Doesn't have to be an insulator as such, just a poor >conductor to adjacent wires. Bullshit, ya fuckin' retard.
From: life imitates life on 20 Feb 2010 14:01
On Sat, 20 Feb 2010 07:46:39 -0800, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Sat, 20 Feb 2010 07:33:54 -0600, "amdx" <amdx(a)knology.net> wrote: > >> >>"life imitates life" <pasticcio(a)thebarattheendoftheuniverse.org> wrote in >>message news:sauun5t4ct7i1ule9dj0lsihmjv5u5ecvs(a)4ax.com... >>> On Fri, 19 Feb 2010 17:57:41 -0800, John Larkin >>> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>> >>>>On Fri, 19 Feb 2010 13:21:36 -0600, "Tim Williams" >>>><tmoranwms(a)charter.net> wrote: >>>> >>>>>Who sells this stuff (without paying for miles at a time)? >>>>> >>>>>I'm especially interested in stupid thick stuff, like, as large as 8AWG >>>>>equivalent. Nebraska Surplus for instance doesn't stock wire like this. >>>>> >>>>>Tim >> >> >>> Trial and error with gauges and strand count do >>> more to optimize the result than ANY specialized, presumed to be required >>> braiding or weaving. The segregation is the key to increasing surface >>> area within a given cumulative "gauge". >> >> No need to do trial and error, Here's a table that gives recommended gauge >>with regard to frequency. >>See Table B. >> http://www.litz-wire.com/technical.html >>Same thing in pdf. >>http://www.litz-wire.com/New%20PDFs/Frequency_Chart_3.01.13.09.pdf >> >>Regarding "ANY specialized, presumed to be required braiding or weaving": >>This is used to equalize proximity effects which equalizes currents in the >>individual wires. >> >>Quote from; http://www.dartmouth.edu/~sullivan/litzwire/skin.html >>"The objective of twisting or weaving litz wire, as opposed to just grouping >>fine conductors together, is to ensure that the strand currents are equal. >>Simple twisted bunched-conductor wire can accomplish this adequately in >>situations where proximity effect would be the only significant problem with >>solid wire. Where skin effect would also be a problem, more complex litz >>constructions can be used to ensure equal strand currents. Thus, in a >>well-designed construction, strand currents are very close to equal." >> > >Yup. He's AlwaysWrong. > >John You're a goddamned retard, Larkin. |