What is present definition of Litz wire? - Page 1
Forum section: electronics / projects

author: mag_therm
author_rank: Frequent Contributor
timestamp: January 01, 2021, 03:59:53 am
content: I read on another thread about a product Litz Type TEX-ELZ consisting of 6 cores of 0.1 mm diameter,wound around a copper core as in the diagram.I don't agree with some of the wiki definition of Litz wire, but do agree with this part:"The result of these winding patterns is to equalize the proportion of the overall lengthover which each strand is at the outside of the conductor."(Search wiki "Litz wire")Can 6 Cores spiralling , in any warp, around a central core meet this definition?Can anybody in the cable industry on here comment?

author: bob91343
author_rank: Super Contributor
timestamp: January 01, 2021, 06:59:07 am
content: This stuff has been around for about 100 years. The essential parts of it are that each strand is insulated from the rest and that the twist is such that every strand spends as much time as any other on the outside of the wrap.I don't know if there is a central core; I don't think so. It's created by a machine. Of course when you connect it you have to strip every strand and solder them all together at each end.I probably haven't answered your question satisfactorily but did the best I could. I would have to dig into one of Terman's books to get more information.

author: Bud
author_rank: Super Contributor
timestamp: January 01, 2021, 08:14:53 am
content: Never seen Litz wire wound around a solid center core. If there was a core it was nylon strands that made the wire soft and flexible.

author: BravoV
author_rank: Super Contributor
timestamp: January 01, 2021, 08:30:59 am
content: Probably just for the audiophoolery related.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 01, 2021, 03:24:42 pm
content: Right, a center wire does very little duty in such a build.I've also taken apart some cable, that looked to be the same build, with each component itself being litz of some size (like 3 x 5 x 22 or something, I don't remember). So they went to the trouble of using proper litz sub-cables, but wound them around a central one that does nothing, or at least much less than it ought to. Go figure. It probably wasn't the most well-considered piece... it may've been China or Taiwan sourced, dunno.NEWT at least doesn't recommend such builds, and typically designs these sorts of cables with 3-5 units in the final braiding step (so none get stuck in the middle).They do have some strange (in the useful way) builds suggested in their catalog -- namely, cables built with rope (insulating fiber) spacers, to further reduce current density and capacitance, for applications where that's advantageous (probably stuff like RF tanks for big transmitters).As for definition, I think it properly has to be multiple units braided. Just a pile of strands, doesn't generally perform all that well (though still better than bare stranded, which is itself noticeably better than solid, FYI). Doesn't matter all that much for small strand counts (like 7), but once you're into the dozens, it starts to matter more and more. The strand size also needs to drop as you get into large counts, as the proximity effect upon every strand dipping into the middle of the cable becomes substantial.So, a typical pattern might be to braid 3-5 units of 5-50 strands each, and 3-5 units of those and so on for larger and larger cables, as needed. The biggest I've handled was... about dick sized, is the easiest way to put it. With a flexible rubber (neoprene?) jacket, it kind of had about that feel to it, too.Tim

author: BravoV
author_rank: Super Contributor
timestamp: January 01, 2021, 03:31:10 pm
content: Quote from: T3sl4co1l on January 01, 2021, 03:24:42 pmWhat was the size again ?

author: madires
author_rank: Super Contributor
timestamp: January 01, 2021, 04:22:02 pm
content: Quote from: BravoV on January 01, 2021, 08:30:59 amShouldn't it be radiophoolery?If the core wire is much larger than the strands it could be to increase the tensile strength of the cable.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 01, 2021, 04:35:05 pm
content: Quote from: madires on January 01, 2021, 04:22:02 pmWhich is done for power transmission: often a steel core is overwound with aluminum strands, for a better compromise between strength, weight and conductivity. (Very pure aluminum is only modestly less conductive than copper, but rather weak; and, when you're carrying thousands of amperes in an arm-sized cable, the skin effect (at mains frequency) is significant enough that the steel core doesn't see much current or magnetic field, and thus loss. That is, the aluminum acts to shield it.)Tim

author: pardo-bsso
author_rank: Frequent Contributor
timestamp: January 01, 2021, 05:26:23 pm
content: Quote from: T3sl4co1l on January 01, 2021, 03:24:42 pmDo you have pictures or more data about how it was used?Asking for a friend. (and myself too)

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 01, 2021, 05:45:11 pm
content: Application was wiring from inverters, to output transformer, in medium size induction heaters. 600A 150kW per inverter module, ganged as needed (scalable design), operation up to 50kHz (with derating). Think the strands were 36AWG, not too fine, suitable for the frequency range (most builds 3-20kHz).The flexibility was also a great aid in how they were used: inverters were joined with 0° power combiners -- these were hand-wound in the assembly, by braiding two cables oppositely through one ferrite core (which were 2-3" o.d.) on their way to the common node (transformer).Use was simple, strip back the rubber jacket, take a suitable (#000 I think) lug, crimp it (make sure all the strands are packed in there), squirt some liquid rosin in, dip in the solder pot and hold until it stops bubbling. Litz is... just about useless without solderable enamel!Tim

author: LaserSteve
author_rank: Super Contributor
timestamp: January 02, 2021, 07:52:01 am
content: What l think of as classic Litz is fine enameled wire with a thin cotton or rayon braided cord wound around each strand for strength and additional insulation. I have childhood memories of how difficult it was to free up and solder all the strands, without breaking them. This was in various shortwave radio kits. It had a definite look of being made on a loom. In other words, the strands were isolated from each other, with the equal length twists."Litzendraught"Steve

author: BravoV
author_rank: Super Contributor
timestamp: January 02, 2021, 08:39:24 am
content: Bought these while ago, left spindle is 80 strands x 0.1mm wires, and the right one is 60 strands x 0.08mm wires, did counted the strand count just for curiosity under microsope.The right one with white jacket is PITA to clean and solder, while the left one was easy, just used a gas lighter to burn off the the tip and all strands can be solder wetted and easily solderable.

author: bson
author_rank: Unknown
timestamp: January 03, 2021, 09:57:23 pm
content: Quote from: madires on January 01, 2021, 04:22:02 pmThat seems very unlikely. If so the natural choice would be some sort of composite - fishing line for example has 5x the tensile strength of steel, is a whole lot more flexible, lighter weight, and isn't conductive. Copper and aluminum are even worse, and both are conductive to boot.

author: madires
author_rank: Super Contributor
timestamp: January 04, 2021, 09:50:53 am
content: Good point! Another possibility could be that the core wire is meant to make the cable less flexible.

author: jonpaul
author_rank: Super Contributor
timestamp: January 04, 2021, 11:50:28 am
content: Hello all:Litz strands are available insulated with solderease, nylease, and other "enamel" to insulate each strand.Cotton or nylon fibers wrap the bundles or the entire cable.Litz reduces the skin effect and proximity effect, most effective 250 kHz-10 MHz depending on wire gauge and current.The RF effective resistance depends on the strand diameter, frequency and the weaving so each strand moves from inside to outside.Indeed spécial wire fab machines are used to fabricate Litz.Notice that merely bunching separate wire strands togather is NOT true litz!For terminating, we use a hot solder pot, fresh flux, dip till fabric wrap and enamel insulation burns off.Remove and clean off residue with x-acto knife or sandpaper.Retwist strands, and resolder in solder pot.Finally, foil conductors can be a better solution.Bon Voeux Année,Jon

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: January 04, 2021, 12:07:27 pm
content: Dose someone happen to know a Chinese supplier of the Litz wires?

author: jonpaul
author_rank: Super Contributor
timestamp: January 04, 2021, 02:50:31 pm
content: Would doubt spec of any Chinese wire for professional applications.Suggest to BUY AMERICAN OR EUROPECHINESE= CHEAP, SLOW, NO RESPONSIBILITYJ

author: SiliconWizard
author_rank: Super Contributor
timestamp: January 04, 2021, 04:32:35 pm
content: Well apart from what's been already said, you'll find what looks like relevant info on Wikipedia:https://en.wikipedia.org/wiki/Litz_wire(haven't read the article thoroughly but what I've read looks accurate enough.)Also, not sure what you mean by "present definition". As bob91343 said, it's pretty old "tech" already, and I see no reason why the definition would have changed.As has been said above, its effectiveness decreases past a certain frequency (depending on the specifics of the wire) due to parasitic capacitance, which can become a serious problem with wires made of a bunch of isolated strands.

author: tooki
author_rank: Super Contributor
timestamp: January 04, 2021, 11:29:52 pm
content: Quote from: mag_therm on January 01, 2021, 03:59:53 amThe only defining characteristic is that each strand is individually insulated.Also, as an FYI, the word "litz" comes from German, where "Litze" means simply "stranded wire", without the individual insulation. The German name for litz wire is "HF-Litze", i.e. "high frequency stranded wire".

author: SiliconWizard
author_rank: Super Contributor
timestamp: January 05, 2021, 12:20:04 am
content: Indeed. The OP didn't say exactly what it was that they didn't agree with - or it was not completely clear, so it's hard to comment further - all we can say is as far as the definition part goes, the Wikipedia article seems to do a good job. The definition is pretty basic as you just said. Now if there are furthers points in the article not directly related to the definition, but to Litz wire design specifics, that's a different story.The question "Can 6 Cores spiralling , in any warp, around a central core meet this definition?" - I can't personally comment on whether this particular design would be good and for what purposes, but if said "cores" are insulated from one another, then I don't see why it wouldn't qualify as Litz wire.