steve@monu6.cc.monash.oz (Steve Balogh) (04/12/90)
In article <3368@optilink.UUCP> elliott@optilink.UUCP (Paul Elliott x225) writes: >coiled kind) and in older telephone handset cords. It is not the same >as Litz wire, since the individual conductors are not insulated (although The individual strands of wire in Litz wire are NOT insulated from each other. Litz wire is essentially LOTS AND LOTS A N D L O T S of very fine (and sometimes silver-coated) wire all twisted together. Because of the greater surface area of such wire, it is supposed to have less impedance at RF frequencies than normal single strand wire. (or wire with only a few strands) By the way, Litz wire tends to be VERY flexible as well due to the large number of strands. Steve ----_--_-_-_--_-__-_------_-__---_-___-_----_-____-_-_--__-_--_--___-_-_-_--__-_ Steve Balogh VK3YMY | steve@monu6.cc.monash.oz (...oz.au) Chisholm Institute of Technology O^O | steve%monu6.cc.monash.oz@uunet.UU.NET PO Box 197, Caulfield East U | ICBM: 37 52 38.8 S 145 02 42.0 E Melbourne, AUSTRALIA. 3145 \_/ | +61 3 573 2266 (Ans Machine) |
jeffw@midas.WR.TEK.COM (Jeff Winslow) (04/13/90)
In article <1990Apr12.071836.17112@monu6.cc.monash.oz> steve@monu6.cc.monash.oz (Steve Balogh) writes: >The individual strands of wire in Litz wire are NOT insulated from each other. >Litz wire is essentially LOTS AND LOTS A N D L O T S of very fine (and >sometimes silver-coated) wire all twisted together. Because of the greater >surface area of such wire, it is supposed to have less impedance at RF >frequencies than normal single strand wire. Oh, really? And how can it have greater (electrical) surface area if all the surfaces are in electrical contact? What keeps the current inside the fine wires and away from the bundle's surface? (Especially if it's silver plated.) Maybe usage varies in different parts of the world, but around here Litz wire is most definitely made up of many fine wires all enamel-insulated from each other, with each wire brought out to the surface periodically. I had a funny feeling about this, due to some unanswered questions about proximity effect (my experience with Litz wire has been limited to few experimental switching- supply designs), so I looked it up in a couple of electronics dictionaries as well. They both indicated specifically that the wires are individually insulated. Jeff Winslow
commgrp@silver.ucs.indiana.edu (BACS Data Communications Group) (04/13/90)
>In article <1990Apr12.071836.17112@monu6.cc.monash.oz> >steve@monu6.cc.monash.oz (Steve Balogh) writes: >>The individual strands of wire in Litz wire are NOT insulated from >>each other. Litz wire is essentially LOTS AND LOTS A N D L O T S >>of very fine (and sometimes silver-coated) wire all twisted >>together. Because of the greater surface area of such wire, it is >>supposed to have less impedance at RF frequencies than normal single >>strand wire. Jeff Winslow replies: >Oh, really? And how can it have greater (electrical) surface area if >all the surfaces are in electrical contact? What keeps the current >inside the fine wires and away from the bundle's surface? (Especially >if it's silver plated.) >Maybe usage varies in different parts of the world... I looked it up >in a couple of electronics dictionaries as well. They both indicated >specifically that the wires are individually insulated. Stranded wire has less skin-effect resistance than the equivalent solid wire, but much more than true litz wire with individually- insulated strands. Some large/expensive stereo speaker cables are being marketed as "Litz" and are made of many very fine (but not individually insulated) strands. Skin-effect resistance can be significant in large-diameter conductors at audio frequencies. Whether it makes noticeable difference over the length of speaker cables is another interminable argument for rec.audio (like the one about mercury-filled plastic tubes which were supposed to give your speakers a more "fluid" sound. :-) Here's a list of AWG copper wire sizes and their "critical frequencies" (frequency above which skin effect causes resistance to be significantly greater than DC resistance). I don't know the criteria for "significantly greater." The table partially reproduced below was in the Canadian LF/VLF newsletter _Northern Observer_ issue #9 (April 1989). AWG dia. critical size mm freq. ---------------------------- 1 7.35 586 Hz 2 6.54 738 4 5.19 1017 6 4.12 1.87 kHz 8 3.26 2.97 10 2.59 4.72 12 2.05 7.50 14 1.63 11.9 16 1.29 19.0 20 .812 48.0 22 .644 76.3 28 .321 307 32 .202 775 36 .127 1.96 MHz 40 .080 4.96 In addition to skin effect, wire resistance can increase by "proximity effect" where a strong magnetic field forces the current toward one side of the conductor. That's a reason why some cyclotron magnets are wound with flat "wire." -- Frank Reid W9MKV reid@ucs.indiana.edu