Can't source gapped EFD15/8/5 core half - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: April 06, 2023, 06:22:03 pm
content: Hi,We need to source the EFD15/8/5 ferrite core half which is gapped to give the AL=63 version (Ferroxcube) or AL=50 version (TDK).We only need two pieces.We must use this part as the transformer cannot be any bigger than EFD15/8/5.Its for a 24V flyback SMPS, of some 20W or so.EFD15/8/5 TDKhttps://www.tdk-electronics.tdk.com/inf/80/db/fer/efd_15_8_5.pdf(N87 or N97 ferrite)EFD15/8/5 Ferroxcubehttps://www.farnell.com/datasheets/1595806.pdf(3C90, 3C94, 3C96, 3F3 or 3F4 ferrite)It is not available anywhere farnell, RS, digikey, mouser, Kaschke, TME , powermagnetics.co.uk , etcElna magnetics will only sell us $500's worth.bfioptilas and ferroxcube i have emailed but no reply yet.Has this part gone obselete?

author: jonpaul
author_rank: Super Contributor
timestamp: April 07, 2023, 06:59:35 am
content: As always another useless FTTS.of course ungapped EFD are easily accessibleput paper or G10 fiberglass gap of desired thickness and adjustable gap for L.We prototyped and manufacted with such ungapped cores for decades, no issues.I expect no useful responsej

author: Faringdon
author_rank: Super Contributor
timestamp: April 09, 2023, 10:16:40 am
content: Thanks, but i need a specific gap, and the core i spec, is an offtheshelf gapped core half.This application is squeezing every spare milliwatt out of the transformer.Does anyone know what the lead time might be on this?...they are out of stock everywhere.

author: pardo-bsso
author_rank: Frequent Contributor
timestamp: April 10, 2023, 03:43:45 pm
content: I'm very sorry to say this, but even in my country if you ask nicely to any supplier you can find a handful of them.

author: dmills
author_rank: Super Contributor
timestamp: April 10, 2023, 06:07:58 pm
content: Find local model engineer with a surface grinder, grind to specified gap, you only want two so... Cost will be a beer or two.Taking half a mm off the centre leg is not exactly the toughest of jobs, I have been known to throw a few tens of turns on a bobbin and set the HP 4192A up next to the grinder if it was something critical, grind, add other core and other half, read, disassemble, grind.Trick is top make sure no grinding dust gets into the cooling fan on the analyser, fixing that shit is annoying.

author: jonpaul
author_rank: Super Contributor
timestamp: April 10, 2023, 09:26:43 pm
content: The gaps are ground and lapped, with a diamond charged tool.In 1970s we worked with ELNA Ferrite lab in Woodstock NY.the DIY gap is prone to breaking or chipped ferrite.The shape mentioned is especially delicate.Over our experience we found little benefits of a center ground gap vs paper or fiberglass spacer across the faces.Big advantage of a spacer is easy adjustable gap size up or down.Thus we stocked ungapped cores and applied spacers in winding and assembly.Jon

author: dmills
author_rank: Super Contributor
timestamp: April 11, 2023, 09:55:45 am
content: Yep, diamond wheel with a not too hard substrate is probably the way, I expect Norton abrasives have something suitable, they usually do.I wonder if you could do it on a tool and cutter grinder instead of the usual surface grinder? Might want coolant is the only thing, and that tends not to be a tool & cutter grinder thing but is totally standard on a surface grinder.Shimming it with something non magnetic is always the easy way for prototyping, then when it is right measure the Al value and get a few hundred made for the pre production run.

author: TimNJ
author_rank: Super Contributor
timestamp: April 11, 2023, 01:13:04 pm
content: I’ve said it many times, but for one or two pieces, don’t overthink it. Get a small diamond or CBN wheel for your Dremel and a small size diamond file. Buy a few core sets as backup, just in case you take a big chunk out by accident. I’ve also done it in the drill press with an aptly sized diamond wheel (with integrated shank). It’s not really rocket science or any more difficult than any other basic mechanical work.

author: TimNJ
author_rank: Super Contributor
timestamp: April 11, 2023, 01:17:36 pm
content: Granted, EFD’s center post cross section can be quite thin compared to the round and square varieties, so maybe you can’t be quite as barbaric as I’ve lead you to believe. But, with decent fixturing, a little bit of thought, and a few broken cores, I think you’ll be alright!

author: jonpaul
author_rank: Super Contributor
timestamp: April 11, 2023, 02:30:25 pm
content: Rebonjour a tous:1/ Gaps: In our magnetics and SMPS/EBU design and mfg (since 1970s!) , we did not find benefits of a custom center leg gap in practice either for mains freq or HF SMPS transformers and inductors.We always had fine results with non mag spacers across core faces.Exception was audio and RF tuned filter and oscillator potcores with adjusters.2/ OP question. response: The tipoff of yet another rabbit hole from the OP:"This application is squeezing every spare milliwatt out of the transformer"FTTS threads and questions are NEVER resolved, regardless of our efforts,I feel that ALL FTTS/Farrington/Treeze posts are clickbait.Has he ever built a working SMPS or magnetic?__________I must depart to do actual work! (production indr procurement, travel logistic, fix TEK2465B)I wish to all an ABSOULTELY FANTASTIC day!Amicalement,Jon

author: floobydust
author_rank: Super Contributor
timestamp: April 11, 2023, 06:01:16 pm
content: You think getting 24W out of this tiny 15mm core is practical?no SMPS is 100% efficient so even the "20W" requirement is wrong, right off the bat.You think the bobbin can fit the wire fill and HV isolation tape etc? 9mm is just massive like a golf courseThis is core is unavailable for a reason, it's to prevent a project disaster lol.

author: jonpaul
author_rank: Super Contributor
timestamp: April 11, 2023, 07:03:51 pm
content: All TDK original info needed here.https://www.tdk-electronics.tdk.com/inf/80/db/fer/efd_15_8_5.pdfNO PC200 matl avail gapped.Power Pfe cal from values gicen at Bmax and Fj

author: Faringdon
author_rank: Super Contributor
timestamp: April 12, 2023, 06:26:52 pm
content: QuoteThanks, yes, we've pegged it back to 17W output at 24Vas attached.Spacers sound good, but we'll never find the exact right thickness needed. Will take ages of adjusting/winding/measuring...etc etc

author: jonpaul
author_rank: Super Contributor
timestamp: April 12, 2023, 06:40:48 pm
content: exact fiberglass and insulating papers are readily available.A production design must have a 10..30% tolerance on any magnetics inductance.j