Beautiful Inductors, Now Not Such A Lost Art

As ferrite technology has progressed into a mastery of magnetic permeability, the size of inductors has gone down to the point at which they are now fairly nondescript components. There was a time though when inductors could be beautiful creations of interleaving layers of copper wire in large air-cored inductors, achieved through clever winding techniques. It’s something that’s attracted the attention of [Brett], who’s produced a machine capable of producing something close to the originals.

Part of the write-up is an investigation of the history, these coils were once present even at the consumer level but are now the preserve of only a few highly secretive companies. They are still worth pursuing though because they can deliver the high “Q” factor that is demanded in a high quality tuned circuit. The rest of the write-up dives in detail into the design of the wire feeder, and the Arduino motor control of the project. There should be enough there for any other experimenters to try their hands at layered inductors, so perhaps we’ll see this lost art make a comeback.

Custom coils are a regular requirement for anything from radios, to musical instruments, to switching power supplies, so it’s not surprising that quite a few projects featuring them have made it here. One of the more unusual of late has been one that winds toroids.

12 thoughts on “Beautiful Inductors, Now Not Such A Lost Art

  1. Nice find Jenny, and the hackadayI/O page contains some nice background. The yt video on his channel has some mesmarising footage. I couldn’t work out the relevance of the 78 degrees the author is on about. angle in relation to what?

    1. Threaded forms should be easy to 3D print. It would also be easy to use a cylindrical ferrite core (hollow center) and glue a phenolic rod inside of it, with the phenolic rod having the threads.

  2. @Jenny List said: “As ferrite technology has progressed into a mastery of magnetic permeability, the size of inductors has gone down to the point at which they are now fairly nondescript components.”

    Not if you even get close to saturating the ferrite or iron-powder core. There is a lot more to consider beyond magnetic permeability when it comes to inductor/transformer design, especially at RF frequencies.

    Where you often see dense-wound coreless inductors (chokes) is in HF/VHF RF power amplifier plate/anode circuits.[1] To suppress self resonance and reduce losses the windings are typically stepped in size and Litz Wire [2] is used.

    * References:

    1. Plate / Anode RF Chokes

    2. Litz Wire

  3. That’s my machine- so I will elaborate and address the comments.

    78* is the angle pitch of the wind, you can read about it in the pdf, but basically a normal coil winds 89* and progresses either left or right to fill out a bobbin, then goes the opposite, normally. This machine takes N total bends, and goes from edge of the bobbin at that angle, lays wire, and then goes opposite and phase shifts the wind slighly to either lay the wire ahead, or behind the previous few lays until it completes a full layer of which I explained in today’s log.

    To add that they can be used as inductors, they also are used for transformers and antennas. Drone posted some good info and is indeed correct, I would like to add that in addition to low intra-winding capacitance and high Q, they actually seem to run at lower resonant frequencies than their ferrite counterparts of equal winding amounts. I said seem, as I am kinda ambiguously assuming based off a few experiments I ran. A pulse transformer I opened up today was solid wire severed with silk or cotton, impregned with paraffin. I’d say it was roughly 2,700 turns as a solid chunk instead of segmented and compatibly a potted flyback that runs similar voltage is larger in size.

    To construct the machine, its simple. You just need 2 NEMA motors, 2 drivers, an arduino and HMI display. A linear rail and everything else inbetween could be anything from junk parts to precise machined setup. I could elaborate upon it’s construction tomorrow. I am still new to hackadayio’s UI. There’s a lot of little things you can do to improve upon the machine.

    Anyways, I’m still working on it. Still adding more information to it to share with everyone all while doing my own experiments and work upon it. There’s just so much info I have in my head that I learned, and discovered and only one me to type it all out, also try to work on improvements. If anyone’s interested in helping me further develop it into a multi-winder machine (air coil, universal, pickup at the moment, maybe toroidal in the future.) I would more than appreciate the help.

    1. Just wanted to say “Thanks” for the follow-up. Always heartening to see makers who are also HaD readers!

      I know it’s well outside of your target project scope, but if you ever consider expanding into the BLDC stator winding area, I – and a few hundred other of my immediate colleagues – would be very interested in any advances you make :)

    2. Well of course a ferrite or iron dust core will have a lot more inductance than an air core of the same diameter and turns. .. Thats the point of using a higher permeability material. The tradeoff is that an air core is totally linear and has no hysteresis, and any core material is the reverse. But the magnetic core means you get by with less wire ,and therefore less series resistance and potentially a higher Q.

  4. Inductors were once wound as a flat disk of wire, spiralling circularly from the centre. They incorporated a mechanism, whereby the spiral could be loosened or tightened, to effect tuning.

    Capacitors were once comprised of rooms filled with arrays of hand-blown glass Leyden jars. The carpentry used to fix these devices was of the highest order.

    1. Then, if you wanted to construct, say, a CW radio station, for the sending and receiving of Morse telegrams, You’d likely need a generator for power. Seed oil Diesel generators weren’t very reliable at the time, so you’d need an enormous number of extremely low energy density, lead acid cells as a back-up.

      If you were really lucky, and lived in a place with utility power, then you’d have to do everything in the dark. Light globe sockets were the only place to ‘plug-in’, and it would be another 15-years before the idea of an appliance socket caught-on.

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.