Litz wire
in [Design]
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From: Jim Thompson on 21 Feb 2010 19:00 On Sun, 21 Feb 2010 17:10:03 -0600, "amdx" <amdx(a)knology.net> wrote: > >"qrk" <SpamTrap(a)spam.net> wrote in message >news:ks63o5p96edftvotfmks3983d8dou0gnq4(a)4ax.com... >> 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 >> > >> What frequency is this for. If you're under 1MHz, you're mainly >> fighting proximity effect, not skin effect. > > Hey qrk, > I haven't seen that information before, do you have anything to site >that would make me believe it? > To quote Dagmargoodboat, [At 290Khz] >"Comparing the braid to the equivalent-cross-section solid wire: > > (view table in Courier font) > > Winding Rac (calculated) >---------- ------------------ >7 x 0,23mm 1.46*Rdc >1 x 0,608 4.29*Rdc > >So, the braid was ~ 3x better. > >Here are a couple of skin effect calculators. >http://daycounter.com/Calculators/SkinEffect/Skin-Effect-Calculator.phtml > http://circuitcalculator.com/wordpress/2007/06/18/skin-effect-calculator/ > > >>To deal with proximity >> effect, all you need is bunched conductors (twisted), not Litz. > > Ok, you need to explain what you mean by bunched conductors, >Are they insulated bunched conductors? > As stated before proximity effect is minimized by making every conductor >find itself in the same position in the bundle an equal amount of time. >Twisting may or may not do that, depends on the amount of conductors >twisted. > Mike > > >> The Litz wire I have come across use bunched groups twisted into a >> larger >> bunched group. This closely approximates Litz. > > Yes, "closely approximates Litz" because it would not be as good >regarding >proximity effect. It doesn't have every conductor find itself in the same >position >in the bundle an equal amount of time. > Mike > > > Clear back in the dark ages, with a 200W off-line SMPS running at 20kHz, I found that winding dissipation in a single strand winding was significant clear up to the 9th harmonic! The melted bobbins drew my attention to calculate that little detail :-( So I switched to Litz and cool transformers. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
From: life imitates life on 21 Feb 2010 19:04 On Sun, 21 Feb 2010 17:10:03 -0600, "amdx" <amdx(a)knology.net> wrote: > As stated before proximity effect is minimized by making every conductor >find itself in the same position in the bundle an equal amount of time. >Twisting may or may not do that, depends on the amount of conductors >twisted. It also depends on what he stated. If the run is short enough it makes no difference. Lower frequencies at lower currents also have less issues with the outward EM field push that we all know as "skin effect". AND the mag field around each individual conductor in a bunch, whether Litz woven or not, will be different than that of the solid, so the EM field effect claimed to also affect non-woven bundles is not as pronounced as you might think. The wires in the centers of non woven bundles do NOT exhibit the same problem that a solid does. It is several parallel fields, not a single conduction field. Yet another reason why the effect is still realized sans the weave. It is not 100% efficient, from that perspective, but it DOES STILL work. It is a fact. Get used to it.
From: George Herold on 21 Feb 2010 19:20 On Feb 21, 1:21 am, life imitates life <pastic...(a)thebarattheendoftheuniverse.org> wrote: > On Sat, 20 Feb 2010 21:22:51 -0800 (PST), George Herold > > > > > > <ggher...(a)gmail.com> wrote: > >On Feb 20, 8:38 am, "dcas...(a)krl.org" <dcas...(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. > > >> Dan- Hide quoted text - > > >> - Show quoted text - > > >Cool, Thanks Dan. I'd never thought of that. > > >A bit OT, but I remember seeing a video of high current experiments > >done at the Magnet Lab, (then at MIT circa 1960's) Where they were > >using several ~2-3" wide strips of copper. > > Flat strip conductors negate skin effect in a similar manner as that of > a Litz wire configuration. The main problem with using it as wire is the > amount of space it takes up on a bobbin per turn. That makes it only > practical used as a hook-up link, or inter-node connection link between > points in a chassis.- Hide quoted text - > > - Show quoted text - Yeah in the video they were using it to hook up various experiments. George H.
From: George Herold on 21 Feb 2010 19:30 On Feb 21, 9:59 am, "amdx" <a...(a)knology.net> wrote: > > 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 > >Yeah, I'm talking about a physics teaching instrument, but they are > >used professionally to measure the Earths magnetic field. > >George H. > > Would you care to share info about the physics teaching instrument? > Mike- Hide quoted text - > > - Show quoted text - Sure here's a link to the Earths fied NMR. http://www.teachspin.com/instruments/efnmr/index.shtml To outer wooden forms are about 2.5 feet in diameter and hold the gradient coils. The NMR coil, wound with litz wire, is in the center of the thing. This is not 'my baby' so I only know the broad details of operation. The two tricks are turning off the polarizing B field 'in the right way'.. proper choice of diodes and R's and the use of noise canceling coils. George H.
From: amdx on 21 Feb 2010 19:57
"life imitates life" <pasticcio(a)thebarattheendoftheuniverse.org> wrote in message news:3kh3o5la77d3spc30sp4vdb381lp5hluuh(a)4ax.com... > On Sun, 21 Feb 2010 17:10:03 -0600, "amdx" <amdx(a)knology.net> wrote: > >> As stated before proximity effect is minimized by making every conductor >>find itself in the same position in the bundle an equal amount of time. >>Twisting may or may not do that, depends on the amount of conductors >>twisted. > > It also depends on what he stated. If the run is short enough it makes > no difference. Lower frequencies at lower currents also have less issues > with the outward EM field push that we all know as "skin effect". > > AND the mag field around each individual conductor in a bunch, whether > Litz woven or not, will be different than that of the solid, so the EM > field effect claimed to also affect non-woven bundles is not as > pronounced as you might think. > > The wires in the centers of non woven bundles do NOT exhibit the same > problem that a solid does. It is several parallel fields, not a single > conduction field. Yet another reason why the effect is still realized > sans the weave. It is not 100% efficient, from that perspective, but it > DOES STILL work. > > It is a fact. Get used to it. I completely agree Jim. I just went on a rant when qrk said, " If you're under 1MHz, you're mainly fighting proximity effect, not skin effect." I don't believe that, and I think a properly sized bundle of twisted (insulated wire) will have a large effect over a solid wire with the same circular mils. (as Dogmargoodboat said, 3x) It would be interesting to find what percentage change a twisted litz would have over a properly braided litz. I'll bet it's under 20%. What do you think? Mike |