Litz wire
in [Design]
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From: John Larkin on 20 Feb 2010 10:46 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
From: Tim Wescott on 20 Feb 2010 13:04 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. -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
From: amdx on 20 Feb 2010 13:16 "Tim Wescott" <tim(a)seemywebsite.com> wrote in message news:oOmdncApB7q4uR3WnZ2dnUVZ_t-pnZ2d(a)web-ster.com... > 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. > Tim Wescott It's just a matter of good, better, and best. Best would be properly braided* and would have the least AC resistance. Mike *I'm not sure braided is the proper term. Each wire needs to have equal exposure to all positions in the bundle.
From: John Larkin on 20 Feb 2010 13:28 On Sat, 20 Feb 2010 12:04:21 -0600, Tim Wescott <tim(a)seemywebsite.com> 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? Insulated strands have much lower eddy current loss than an equivalent big fat wire. Maybe less skin loss too. > >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. As I understand it, if you do the multi-strand thing, the inner conductors can conduct less at high frequencies, for some magnetic reason. Litz braiding gives each conductor equal exposure. Loss goes as I^2, so it's good to keep the currents balanced. But the simple multi-strand thing has higher copper density and shorter path length than braided Litz, and low eddy-current loss, so it's usually good enough. Copper loss will balance the currents some, too. It's also easier to use than solid #8 or true Litz. Litz was really good for super-high Q inductors, like pot cores for low-frequency passive filters. That's a dying art, given active filters. I've seen really sloppy multistrand windings in SMPS inductors, not even twisted, just sort of all over the place. That may result in Litz-like current equilization. John
From: amdx on 20 Feb 2010 13:33
"George Herold" <ggherold(a)gmail.com> wrote in message news:0f405a17-6cbb-4cce-8418-3423e0de508e(a)t42g2000vbt.googlegroups.com... On Feb 19, 5:18 pm, "Tim Williams" <tmoran...(a)charter.net> 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 > > -- > Deep Friar: a very philosophical monk. > Website:http://webpages.charter.net/dawill/tmoranwms The copper rope is not long enough? We've got some discard litz wire, but not nearly that thin or as many strands. We use it to make high Q coils to detect the nuclear magnetic moments of protons spinning in the Earth's B field. Frequencies a bit above 2kHz. And lots smaller currents. Well the same coils polarize the spins, but that's 3 amps at DC. George H. Hi George, Is this used in a magnetometer? There is a thread on rec.radio.amateur.antenna with the subject: Carl and Jerry Magnetometer, that has a discussion about about picking up the precession of the proton as it returns back to alignment with the earths magnetic field. I found it very interesting, probably because I knew zero about the subject. If you have anything to add to that thread, please do so. Mike |