Litz wire for use in  Boost PFC inductor winding?....no informative datasheets  - Page 1
Forum section: electronics / general

author: opampsmoker
author_rank: Regular Contributor
timestamp: December 27, 2020, 10:21:11 pm
content: Hi,Does Anybody know of any off-the-shelf vendors of Litz wire for winding of Boost PFC inductors? (We need Litz as the coil will be near a gap in the ferrite and exposed to the fringing field)We know of Furukawa TEX-ELZ, but we don’t need the triple insulation, and would like more strands than the seven that TEX-ELZ gives….TEX-ELW TIW Litz:https://www.furukawa.co.jp/tex-e/en/product/texelz.htmlOther than Furukawa, none of the Litz wire vendors offer a Litz wire datasheet with sufficient info on it for you to decide if the wires were suitable or not (eg, they don’t give the insulation rating, don’t say if its solderable, don’t give the overall max outer diameter, etc etc).Power integrations recommend “served Litz Wire” (anything from 40 to 60 strands of AWG38) in all of their PFC Application notes eg DER-484. I contacted Power integrations for the part number, and they just gave me two company names, “mwswire.com” and “newenglandwire.com”. However, I contacted mwswire.com, and they just emailed me back and told me to ask Power integrations which Litz wire part number they were referring to.Does anybody know of any Litz datasheets for offtheshelf Litz wire that we can look at?We need an insulation test rating of 500VAC for 1 minute at <500uA.

author: TimNJ
author_rank: Super Contributor
timestamp: December 31, 2020, 06:11:50 pm
content: Between which terminals/points are you trying to measure dielectric withstand/insulation strength?Do you mean you want to check if the litz will break down between strands within the inductor, or a turn-to-turn short, etc.? I've not seen an intra-winding breakdown issue, even with un-served litz, for mains voltage PFC circuits (yet). While it depends heavily on the inductor style and winding structure, often times the ΔV between any two parts of the winding (in close contact with each other) will not be so high. Let's say you have 5 layers of wire, with 500V across the entire winding, then let's estimate that each layer is about 100V apart from the adjacent layer. 100V is pretty trivial for enamel insulation, so it should be fine.The main parts to worry about in inductor design are...1. Pin terminations. When enameled wire (including litz) is soldered to coil-former/bobbin pins, it's almost always by dunking the inductor into a molten solder-pot. Sometimes, the solder wicks up the wire (into the coil structure), burning off more enamel than you'd like. Now you may have un-insulated wire inside the inductor. So, most (decent) manufacturers put some Teflon tubing over the wires near the the pin termination. For an "average" sized inductor, maybe about 10mm of it.2. Any time a wire traverses the main direction of winding at 90°. Let's say a winding finishes at the top of the bobbin, but you need to make a connection to the pins on the bottom. To bring the wire down to the pins, the wire passes over the coil orthogonally. Experience shows that enameled wires at 90° angles are more likely to fail via abrasion. So, similar to the above, make sure to add some Teflon tube before bringing the wire across the coil.If you use served litz, much less worry about intra-winding shorts, but it will affect your copper fill density. For maximum performance, you generally want to maximize cross-sectional area of the conductor. When you add serving, you not only add extra material, but you also force a more circular cross-section of the wire, as opposed to non-served litz which can squish down to a more ovular, or even rectangular cross-section. The area between the circular cross-sections is wasted space, but non-served litz can often fill these voids.By the way, enamel insulation is never considered anything more than "functional insulation", that is, it does not provide any "real" insulation in the eyes of industry safety standards. It is just meant to allow the circuit to work. On the other hand TIW litz actually provides insulation per IEC standards. For this reason, you may be less likely to find data on standard enamel wire compared to TIW litz, which performs a function directly related to safety/isolation.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 31, 2020, 07:00:39 pm
content: Uk supplier :https://www.wires.co.uk/acatalog/litzwire.html

author: mag_therm
author_rank: Frequent Contributor
timestamp: December 31, 2020, 11:43:47 pm
content: Quote from: opampsmoker on December 27, 2020, 10:21:11 pmEach Litz conductor used to be a a contiguous conductor dedicated to one winding.I hope that is still the case. (?)I never heard of splitting a litz cable into multiple windings.To get that insulation level for safety standards, I think you will need properly rated inter-winding insulation whether using litz or strands of enamelled solid.

author: opampsmoker
author_rank: Regular Contributor
timestamp: January 01, 2021, 12:45:13 am
content: QuoteThanks, we cant find any datasheets as described above on wires.co.ukQuoteThanks, the only TIW Litz wire we can find on the web is the Furukawa TEX-ELZ, but unfortunately it only has 7 strands.

author: TimNJ
author_rank: Super Contributor
timestamp: January 03, 2021, 05:00:29 am
content: Quote from: opampsmoker on January 01, 2021, 12:45:13 amSee this thread:https://www.eevblog.com/forum/renewable-energy/triple-insulated-litz/msg2749224/#msg2749224

author: Terry Bites
author_rank: Super Contributor
timestamp: January 05, 2021, 04:31:58 pm
content: Here's a starting pointhttps://www.newenglandwire.com/product/litz-wire-types-and-constructions/for local distributorswww.newenglandwire.com/find-a-manufacturers-representativeloads of info on their site

author: Muzzer
author_rank: Newbie
timestamp: January 07, 2021, 11:34:46 am
content: The other candidate is usually Rubaduehttps://www.rubadue.com/our-wires/triple-insulated-wire/