Litz wire
in [Design]
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From: Ross Herbert on 20 Feb 2010 05:24 On Fri, 19 Feb 2010 21:14:27 -0800, life imitates life <pasticcio(a)thebarattheendoftheuniverse.org> wrote: :On Fri, 19 Feb 2010 16:18:49 -0600, "Tim Williams" :<tmoranwms(a)charter.net> wrote: : :>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. : : : The problem is that it not being constructed from individual mag wires, :it is "seen" as a single strand to the current flow, and having only ONE :skin. The litz configuration requires the wire be discreet from each :other with the exception of the termination points. I hope you don't mind a little bit of layman's interpretation as an assistance to the OP but what you mean by "mag wire" is that each individual strand which makes up the total x-sectional area of the litz conductor MUST be insulated from every other strand. If the strands aren't insulated then the skin effect will be the same as if a single strand of the same overall x-sectional area had been used - and this is no good for high frequencies.
From: life imitates life on 20 Feb 2010 07:18 On Sat, 20 Feb 2010 10:24:28 GMT, Ross Herbert <rherber1(a)bigpond.net.au> wrote: >On Fri, 19 Feb 2010 21:14:27 -0800, life imitates life ><pasticcio(a)thebarattheendoftheuniverse.org> wrote: > >:On Fri, 19 Feb 2010 16:18:49 -0600, "Tim Williams" >:<tmoranwms(a)charter.net> wrote: >: >:>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. >: >: >: The problem is that it not being constructed from individual mag wires, >:it is "seen" as a single strand to the current flow, and having only ONE >:skin. The litz configuration requires the wire be discreet from each >:other with the exception of the termination points. > > >I hope you don't mind a little bit of layman's interpretation as an assistance >to the OP but what you mean by "mag wire" is that each individual strand which >makes up the total x-sectional area of the litz conductor MUST be insulated from >every other strand. If the strands aren't insulated then the skin effect will be >the same as if a single strand of the same overall x-sectional area had been >used - and this is no good for high frequencies. Exactly. I do not word things well on the fly. I do far better as a proofreader of other's works or even my own work, upon subsequent re-examination
From: amdx on 20 Feb 2010 08:33 "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
From: dcaster on 20 Feb 2010 08:38 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
From: legg on 20 Feb 2010 09:12
On Fri, 19 Feb 2010 16:18:49 -0600, "Tim Williams" <tmoranwms(a)charter.net> wrote: >"George Herold" <ggherold(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. It might serve if you can decouple the strands. 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. The actual aim of the 'twist' is to have strands in any particular bundle or strand at near-right angles to those on the opposing surface, as the twist pattern is scaled up. If the twist direction is reversed on each level of build-up, surface strands will always appear to be pointed in the approximate direction of current flow, and the structure itself will not 'bind'. RL |