Sourcing/Designing High Power Edge Wound Inductors - Page 1
Forum section: electronics / rf-microwave

author: W2DML
author_rank: Contributor
timestamp: May 30, 2024, 02:00:46 pm
content: Hello,Does anyone have any literature or resources on designing an edge wound inductor? Similar to thishttps://www.rfparts.com/coils-and-coil-form/8911553-13-p.htmlIs there any companies that still make these? This is for a High Power(120kW) RF Amp I'm in the process of designing. I would be using these for the Anode Choke circuit.

author: mag_therm
author_rank: Frequent Contributor
timestamp: May 30, 2024, 07:17:32 pm
content: Try Jackson Transformer Co, Florida.They can do the edge-wise winding.

author: mark03
author_rank: Frequent Contributor
timestamp: May 31, 2024, 04:09:02 pm
content: Sounds like a job for 3D printing (the frame, that is)?

author: PartialDischarge
author_rank: Super Contributor
timestamp: May 31, 2024, 05:09:31 pm
content: This company in Hungary does chokes and inductors that wayhttp://www.ajka-trafos.com

author: W2DML
author_rank: Contributor
timestamp: May 31, 2024, 06:56:41 pm
content: Thank you everyone for the suggestions, I will reach out to these companies. Has anyone had experienced making one of these from scratch? I need this inductor have an SRF above 50 MHz & withstand voltages of 20kV, 20A. The high power RF tetrode industry isn't really around so it seems many of these companies don't exist or were acquired and changed. In one of our existing systems we use one from Cardwell Condensor Corp. for example.

author: CaptDon
author_rank: Super Contributor
timestamp: June 03, 2024, 10:12:04 pm
content: Yes, these edge wound coils are used in the phasing arrays for directional antenna arrays and as impedance matching 'geep' coils. I wish I could remember the business name for Ron Racleigh (probably spelled wrong). He was nationally known for phasor designs and construction. Ron lived in Texas. Also, the big tetrodes are still around but were NEVER cheap!! Contact Fred Wise (Wise Electronics) in Windsor (York County) Pennsylvania. Fred has built short wave transmitters (WGCB /WINB). He could help you. If you can chat a bit, who for and what for 120KW??? Almost no one except the tax payer supported military puts such large power into the ether anymore. With modulation modes that can be detected below ambient noise floor high power just isn't the norm anymore. I assume Econco and Burle still make big tetrodes? Eimac (God rest the original souls) made tetrodes with plate dissipation up to the megawatt range with vapor phase or water cooling. You are designing this transmitter??? You couldn't buy it from Nautel, Continental, CSI or even find a modifiable big shortwave transmitter on the surplus market? Hundreds of them have been scrapped due mostly to internet streaming being much much more cost efficient. Iceland scrapped nearly everything out at Vatnsendi!! You have me curious? I spent 13 years at a 50KW facility. With today's power combiners you would probably build two 60KW machines and combine them. Or maybe 3 or 4 30KW solid state units and a combiner. These days the warm glow of tubes is extremely expensive!!!

author: CaptDon
author_rank: Super Contributor
timestamp: June 06, 2024, 02:03:58 pm
content: No reply??? Did you contact Ron or Fred?? You are designing a 120KW transmitter? At that power level, unless you had previous design work at that power level I wouldn't trust your design. 120KW from a single final stage? Rarely done in the last 40 years unless it is for pulse work. 20KV at 20 amps....That is 400,000 watts? If it is for pulse work the high voltage requirement makes sense but the average current would be far less. 400KW capability on the D.C. input with 120KW out? You still have me curious, who for and what for using this design? Are you sure after a very high power untested design where everything is hyper critical to get right that it won't simply be a very expensive blow up or unreliable? There have been a lot of notorius 'Big Bang' unreliable transmitter designs even from the pros!! Saw a Gates / Harris burn to a complete crisp!! RCA Ampliphase (Amplifuzz) were costly failures. What final, 4CW100,000? 4CV250,000? Water or vapor phase cooling? Final cost projection including plate power transformer, chokes, high voltage capacitor bank, tetrode driver & final, exciter, sockets, Big blowers / radiators / water pumps / de-ionized water loops and isolators. Wow....500 Kilobucks minimum. I've been away from it for far to many years but I remember there were companies specializing in the resale of decommissioned parts from 100KW to 500KW international shortwave broadcast transmitters. It was always fun to show my friends how it was possible to 'light your way' after dark through the field under a 50KW rhombic antenna with a burned out 4ft flourescent lamp!!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 06, 2024, 02:21:13 pm
content: Or perhaps industrial (dielectric heating), that might explain the fairly high frequency and (potential, or assumed) unsuitability of MOSFETs.Not sure if you know, but tubing is highly effective for inductors; Q will be higher than for edge-wound. Unless you need to make a variable (roller) type for which tubing might be unsuitable. Note that a copper slug can be moved into the coil for similar effect, without too much impact on Q. They're not hard to make either way, again unless you need more precision such as a roller might want.Certainly no big deal to make in-house compared to other maintenance resources (what works for copper plumbing, works for electrical tubing; solder and braze are typical joining means) or tooling (a basic machine shop can do it). And considering the budget overall (as above, or even if strongly discounted by way of being for service rather than new install), there's plenty of room there to get a part designed or build a few yourself.Tim

author: johansen
author_rank: Super Contributor
timestamp: June 06, 2024, 06:46:57 pm
content: Quote from: T3sl4co1l on June 06, 2024, 02:21:13 pmno reason you couldn't use a roller to tap an inductor made from tubing. might want to use a copper laminated brush or something instead but that wouldn't be great for the silver plating rubbing off.I'm curious as to why you think tubing would have a higher Q than edge wound. Seems to me the current would be concentrated on the inner facing edges of the tubing due to proximity effect, and also concentrated on the inner edge as it would be with edge wound anyways. so if you compare an edge wound squished tube of the same dimensions and inductance as a helix of tubing.. seems to me the edge wound should have lower proximity current effect producing higher resistance. It should also have slightly lower turn to turn capacitance due to the increased space between turns.This website suggests he's measured Q as high as 1100 for tubing and 900 for edge wound, but this may have to do with just what he's been able to get hands on and measure, and I presume it is very difficult to measure the difference between an 1100 Q and a 900.https://www.w8ji.com/loading_inductors.htmI wonder if one issue might be edge winding work hardens the copper and increases its resistance.I wonder what a practical Q be if you were to take a bundle of say,24 gauge wires, twist them together, and fit them into a coil form to make an edge wound, continuously interposed inductor.

author: CaptDon
author_rank: Super Contributor
timestamp: June 06, 2024, 09:25:29 pm
content: I definitely agree on the use of copper tubing!! It was very common in the older high power shortwave stations. Wouldn't the 'skin effect' dictate that most of the current would flow on the outside of the tube as opposed to the inside? Looking at the surface area of a 1/2" diameter copper tube vs. a 1/2" by 1/8" flat copper tells a big story. Is my math correct 1/2" tube = 1.57" surface vs. 1/2 X 1/8 = 1.25". Silver plate the copper tube and we have a traditional hands down winner. I have seen some of those coiled tubing inductors tuned with ferrite bars being lowered into the center of the coil. In fact it was three ferrite bars about 14" long and each about 1" in diameter grouped together as one 14" tuning slug. The ferrite bars did not touch each other but had about 1/4" spacing between them. Sort of formed a cloverleaf pattern.

author: johansen
author_rank: Super Contributor
timestamp: June 06, 2024, 11:23:59 pm
content: Quote from: CaptDon on June 06, 2024, 09:25:29 pmread here for what i'm talking about with regard to proximity effect of round vs flat.https://www.e-magnetica.pl/doku.php/proximity_effectAt 1MHZ the skin depth is just 0.08mm

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 07, 2024, 02:00:57 am
content: Quote from: johansen on June 06, 2024, 06:46:57 pmYes, exactly: curvature matters. Magnetic fields more or less "want" to be round, and a square boundary condition makes friction (so to speak, but in this case kind of literally as well).Somewhat obscure but visceral illustration: if you put a steel cylinder inside a moderately-close-fitting induction coil, made with square tubing, and hit it with a good couple 10kW, you know, like you do... you see the image currents from the corners of the tubing lighting up much faster. Before the whole cylinder melts away like 20s later or whatever, but in those first moments when it starts glowing, yeah.Whereas with a round tubing coil, you see the cylinder light up under the tubing, in a fairly rounded manner.The real zinger is, the image current from each corner is visible. You get two peaks from both edges of each turn, rather than just one peak right underneath the round.So, you get more current density in the corners, than you do the inside-ish edge-ish of the tubing, and for conductor of the same cross-sectional area (based on the outer perimeter, i.e. ignoring if it's hollow tubing or solid) you get more loss with the square corners than round.This doesn't change when cores are used; the popularity of edge-wound inductors is a matter of optimizing DCR, and while they can offer pretty nice Q at AC, it's still something you want to use at a lower ripple fraction to keep efficiency up. The main limitation is the air gap: the fringing field intersects the windings, and the windings being solid, there's nowhere for the field to go, it crashes right into the solid metal surface, inducing eddy currents. I did an LLC converter with planar transformer recently, where the Lm-mode Q factor went from ~150 with a single gap, to ~400 with a proprietary solution.QuoteThat sounds about right. The other thing is, you need the winding pitch about twice the diameter (or for strip, effective diameter: imagine something like, a bit smaller than the bounding circle) to optimize Q: permit enough space for field to flow around wire, between turns, and yes this necessarily increases leakage (more leakage means less mutual inductance, total L drops), but it reduces eddy currents faster at first, so Q is improved.We don't do this [modest pitch winding] for standard PCB and SMPS components, because size and cost dominate over Q, and there's no space to spare inside a ferrite core anyway. Again, DCR generally gets priority.Work hardening may be relevant; it's a smaller fraction though, I think -- for copper, more like 5%, so a contributor to the total ~20% difference, but the geometry is still dominant.Or if that was comparing to one with finer pitch, or smaller diameter wire, it could go either way. A 20% difference feels very neither-here-nor-there; both inductors are quite good in general (~1k is bragging-rights territory), and making a subtle change like pitch, conductor diameter (or strip aspect ratio for that matter), or even just a modest change to diameter or length, has a comparable impact on Q.Quote24AWG isn't very much -- crowding dominates over interleave pretty quickly, but that would be okay for a few kHz. Count matters: 10 or 20 strands may well be worse than 1-3 strands of equal cross section; once you get into the hundreds of strands count, litz gets properly effective. (Or for something you might otherwise choose tubing, tens of thousands, easily! We used broom-handle-sized litz cables to wire up induction power supplies, back at PPoE. That was the floor-standing power supplies, 600A IGBT modules, which ran up to 50kHz or so, and I think used 36AWG strands.)Also hard to twist wires into a rectangular form -- especially as stiff as 24AWG. Practical problem, perhaps,but there are actually rolled, crushed or otherwise formed litz cables available. Fairly specialized I think, not something you'll just run across, but I have a random sample in my collection that came from NEWT; it is what it says it is.Litz probably isn't relevant here [in this thread], as it becomes ineffective above some MHz: the necessary stranding becomes too fine (it's harder to get e.g. 46AWG, or more, not to mention handling it), and the voltage between strands increases to such a point that the skin effect around the cable itself -- now due to dielectric as well as resistive losses -- starts to support eddy currents, and the cable looks like a round wire again, no not wholly so, not suddenly, but that there is some shielding effect again, where magnetic field becomes excluded from the middle, and you get skin effect and (small loop) eddy currents.To be more clear about that: what litz is, is, we want a conductor transparent to magnetic fields, yet which supports longitudinal current. It's an anisotropic conductor. At lower frequencies, we get a large anisotropy ratio, and performance is good: we can pack a lot of metal into a small space and not worry about eddy currents. As frequency rises, the ratio shrinks, and we can only try so hard before wires get too fine, or insulation too thin, or packing density drops anyway.At this point (somewhere in the mid 1s to low 10s MHz), a solid-wire inductor with judicious pitch, and maybe a powder core loading it, does very well already, and it isn't a big deal to use the solid wire, versus putting in heroic effort to use litz.Tim

author: pdeal
author_rank: Contributor
timestamp: June 11, 2024, 11:40:32 pm
content: I think Kintronic labs makes them. They’re not cheap though.

author: W2DML
author_rank: Contributor
timestamp: June 12, 2024, 03:10:12 pm
content: Quote from: CaptDon on June 03, 2024, 10:12:04 pmThis is for a particle accelerator, so you are not totally wrong about the who.Quote from: CaptDon on June 03, 2024, 10:12:04 pmThe plan is to use a Eimac 4CW150,000E, a tube we're familiar with and is still used in our facility. Due to the operating frequency we can not use solid state (24.6 MHz, 49 MHz) due to lack of a circulator at those frequencies. RF Cavities will have reflections that tubes can handle but solid state can not. Designing a new tetrode system is hard, especially since a lot of companies used in previous designs no longer exist. We have a surplus of old components but I don't feel comfortable building a design off of NOS parts, don't want to run into scenarios where we can't acquire spares.Quote from: CaptDon on June 06, 2024, 02:03:58 pmSorry, I didn't have a chance to visit the forums since these new replies. The tube will be water cooled, we have experience with these and are looking into making a new amplifier design. The amp will be class AB1, driving CW RF.Quote from: pdeal on June 11, 2024, 11:40:32 pmI've reached out to them and am waiting on a quote.Appreciate everyone for the help and replies

author: CaptDon
author_rank: Super Contributor
timestamp: June 15, 2024, 01:20:20 pm
content: I was sadly informed that Ron Rackley has passed away in 2019. The article was in Radio World magazine. I got out of commercial transmitters and commercial broadcasting many years back and went into locomotive E.C.U. design for G.E. (Great Explosions). I have kept active in ham radio and with my friends in commercial broadcast. Sadly, this was the first I had heard of Ron's passing. He would have been a great help to the O.P.!! Getting old sucks!! I have lost so many mentors and their vast experience and knowledge!! Sad that these greenhorn college engineers have to learn the same mistakes all over again!! I used to see a design that was flawed in so many ways and I would try to inform 'Mr. Greenhorn' of the mistakes. I was almost always greeted with "You're old school educated, this is the way we are taught to do it now". Yes indeed, that is how you are taught, by a bunch of folks who never worked in the field. The old "I'm an engineer, my degree says so". But sadly they were never a technician who suffered through endless trials and tribulations of fixing or modifying poor designs and learning what constitutes a poor design. Was it Einstein who said "So soon old and so late smart"?