Litz wire
in [Design]
|
From: E on 21 Feb 2010 06:24 "Tim Williams" <tmoranwms(a)charter.net> kirjoitti viestiss�:hlqjpu$bi8$1(a)news.eternal-september.org... > "life imitates life" <pasticcio(a)thebarattheendoftheuniverse.org> wrote in > message news:l2k1o55q5ltrjmfr8babnajonp2amtlv4t(a)4ax.com... >> 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. > > Not really... I'm going to use 1.00 x 0.040" copper strap on a high amp > transformer I'm planning. 5V 100A in two turns. > > Tim > I have seen that kind of copper foil conductors used in some ATX power supplies. Don't remember how many turns as I was only interested in the ferrite core for other projects. -ek
From: amdx on 21 Feb 2010 09:59 > 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
From: dagmargoodboat on 21 Feb 2010 11:06 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. Both methods provide more surface area in which surface currents can flow, lowering Rac. Or, if you prefer, they've got more skin in the game. Flat conductors have the advantage of greater cross sectional area in limited winding windows (vs litz, where the stranding's insulation winds up gobbling a lot of the cross section, crowding out copper). Flat conductors also transport heat out of the transformer much more effectively. With litz the cross-sectional area lost to insulation increases both Rac and Rdc, so, for power applications with limited winding windows it can actually be counter-productive--for a given insulation thickness and skin depth there's an optimum strand size and number. In practice, I braided my own 'litz' once to reduce copper loss in a 200-300KHz-ish converter. I think I used 9 strands of #29 solid copper magnet wire, braided to guide each strand through the bundle appropriately, then compared loss to actual super-fine litz. No difference detectable. So, not perfect, but good enough. I wound up just using an even fatter gauge of solid copper magnet wire--easier, and nearly as good. -- Cheers, James Arthur
From: dagmargoodboat on 21 Feb 2010 12:35 On Feb 21, 11:06 am, dagmargoodb...(a)yahoo.com wrote: > In practice, I braided my own 'litz' once to reduce copper loss in a > 200-300KHz-ish converter. I think I used 9 strands of #29 solid > copper magnet wire, braided to guide each strand through the bundle > appropriately, then compared loss to actual super-fine litz. No > difference detectable. So, not perfect, but good enough. To put a finer point on it, I checked my notes. The wire was braided from 7 strands of 0,23mm diameter (31AWG) solid copper magnet wire. The inductor used one layer of 5 turns, for Rdc <4 milliohms. f = 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. -- Cheers, James Arthur
From: legg on 21 Feb 2010 14:25
On Sat, 20 Feb 2010 22:18:28 -0800, life imitates life <pasticcio(a)thebarattheendoftheuniverse.org> wrote: >On Sat, 20 Feb 2010 23:55:18 -0500, legg <legg(a)nospam.magma.ca> wrote: > >>On Sat, 20 Feb 2010 10:58:17 -0800, life imitates life >><pasticcio(a)thebarattheendoftheuniverse.org> wrote: >> >>>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. >> >>Not so much words on the fly, but flies on the words, it seems. >> >>You could also vacuum impregnate the bundle, if it's already formed >>into position (and if you've got a really good impregnation process >>cooking). >> >>RL > > No, you cannot. It only works with insulated strands. Trying to come >up with an 'insulation on the fly method is just plain stupid. buzz buzz buzz. RL |