How do "Goofy-Wound" Inductors Work? - Page 1
Forum section: electronics / projects

author: SuzyC
author_rank: Frequent Contributor
timestamp: January 10, 2019, 11:29:22 pm
content: We have all seen a lot of info about different inductors, but what about "Goofy-Wound" inductors?Suppose we have a toroidial core and I wind half the total winding in one direction and the remainder in the opposite direction(changing from CW winding to CCW).What is the inductance and behavior of such a hybrid?Would such an inductor have a practical application?

author: ArthurDent
author_rank: Super Contributor
timestamp: January 11, 2019, 12:15:50 am
content: Some wirewound resistors are wound that way (but not on metal cores) to be non-inductive.

author: beanflying
author_rank: Super Contributor
timestamp: January 11, 2019, 12:18:37 am
content: Yep generally not an inductor but a wirewound resistor with a very low inductance.Inductor use discussed herehttps://en.wikipedia.org/wiki/Bifilar_coil

author: SuzyC
author_rank: Frequent Contributor
timestamp: January 11, 2019, 12:20:13 am
content: Thanks AuthorDent, I know about that.Why so little mention or interest about the use and characteristics of this kind of inductor?But what can be the use and advantage of an inductor like this that has a practical use in a circuit, besides self-cancellation of parasitic inductance in a power resistor?Since the type of inductor I describe theoretically has zero inductance, is energy stored in the core or lost to the core?I saw on the web of Ayrton-Perry winding of long-wire length inductors with zero inductance.https://en.wikipedia.org/wiki/Ayrton-Perry_windingCould hi-frequency antenna cables or antennas be improved with such inductors as wires to achieve coupling and phasing different elements of a long multi-element antenna(yagi)?How would a yagi-like multi-element antenna work with this type of inductor creating the driven/reflector/parasitic elements?How would this idea work as a way of coupling (optimally delivering power) between stages of a UHF/microwave amplifier or in making slotted-lines/directional couplers?How could such a thing be of practical use in a SMPS?Would this idea (Ayrton-Perry) winding work well to deliver high-frequency pulses over a long distance without inductive delay(like in phasing very high-power lasers in fusion reactor research)?What about a use as speaker cables in large theaters?What would be the behavior of a shielded coax cable with the center conductor wound this way(Ayrton-Perry)?And unanswered: if Ayrton-Perry winding is used, does this type of winding hold the magnetic flux to the center of the winding and prevent magnetic fields to be created and affecting things?If this type of inductor creates magnetic flux in a core, does the net magnetizing power express itself as a power loss?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 11, 2019, 12:43:53 am
content: https://en.wikipedia.org/wiki/Toroidal_inductors_and_transformers#Total_B_field_confinement_by_toroidal_inductorsClasp your right hand around the core, fingers pointing in the direction of the wire going from start to finish; your thumb points in the direction of flux generated with a positive current in that direction.If you reverse the direction of the winding, your thumb will be pointing opposite, and turns will cancel out.The distribution of turns over the bobbin or ring doesn't matter as much, except for the above illustrated case, and for higher-order effects like equivalent capacitance, and cutoff frequency.Tim

author: SuzyC
author_rank: Frequent Contributor
timestamp: January 11, 2019, 12:51:31 am
content: Thanks again, T3sl4co1l. I knew this, that's why I started thinking about this type of inductor and I thought about about how this type of non-inductance inductor finds its place in electronic circuitry. (see my last reply, above).

author: ejeffrey
author_rank: Super Contributor
timestamp: January 11, 2019, 01:02:08 am
content: But why? Such a configuration has very low inductance relative to a normal inductor constructed the same way, but still more than zero and more than a straight wire. It will be unnecessarily large, have poor parasitics, and lower Q than an inductor of the same value constructed another way (such as an air core inductor).With a power resistor, the goal is to get a certain amount of wire to get the resistance and power handling you want. The non inductive winding is a way to get X meters of wire in a small volume with low inductance.

author: SuzyC
author_rank: Frequent Contributor
timestamp: January 11, 2019, 01:12:10 am
content: Thanks ejeffrey, but unlike a bare wire over a distance, how would the radiation of magnetic or RF energy (or preventing stray RF pickup) be affected by such a long wire?Your reply makes the most good sense!But I like to entertain out-of-the-box ideas!But what did Ayrton-Perry have in mind for practical uses of this type of inductor?Uhmm, Tesla played with this idea.But still, I am curious:What about if this type of center conductor found itself inside a coaxial cable?And what would be the difference if it was to used in creating a uhf/microwave antenna element?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 11, 2019, 01:34:29 am
content: If you mean equal parts forward and backwards wound, like an Ayerton-Perry construction, that isn't an inductor, it's a resistor with a circular cross section. It has no interesting properties beyond a chunk of metal the same overall geometry.If you keep the wires separate, and look at the impedance between them, you have, not an inductor, but (drumroll) -- a transmission line! As a TL, normally you'd not have the wires moving away and towards each other, but paired together, say as a bifilar winding.What's the difference, then? At medium frequencies, the TL impedance is the average from the geometry (wires far apart have higher impedance; closer, lower), while at high frequencies the periodic change in impedance gives a bandstop filter effect. Meanwhile, the TL being wound up in a helix puts a lot of turns near each other, which changes the velocity and dispersion characteristics.All TLs have the characteristic that, at low frequencies, they have equivalent capacitance in parallel between wires, and inductance in series along them. Indeed, anything with physical dimensions does, so keep in mind that any real "resistor" contains some inductance and capacitance as well!Tim

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 11, 2019, 01:45:40 am
content: Quote from: SuzyC on January 11, 2019, 01:12:10 amIt's not an inductor... not primarily, and not intentionally. There's a reason it's called anoninductive resistor.As I mentioned, everything has inductance, and this construction cannot eliminate inductance. It's a big difference compared to a single helix, but not a complete cancellation.An "inductor" is not anything that's wire spooled up around. It has to be done correctly too!QuoteNothing. Cancellation of local fields means no radiating field.Tim

author: SuzyC
author_rank: Frequent Contributor
timestamp: January 11, 2019, 01:59:19 am
content: T3sl4co1l, thanks again for soothing my damaged brain.But since this type of wiring cancels the magnetic field,is energy lost in the process due to flux creation/cancellation?Would a receiver antenna elementmade this way just behave like a straight piece of wire( or just like hay-wire)?You are saying then that such an inductor has almost no practical use, with lengths of wire the optimal substitute in any circuit or device?Isn't cancellation of local fields means no radiating field a very useful property for transmitting energy in a very sensitive or high-power RF circuit or even in a power transmission line?

author: cdev
author_rank: Super Contributor
timestamp: January 11, 2019, 02:01:20 am
content: Is something like this what you mean?They actually cancel out!The word you may be looking for isvariometer.This is not the world's best variable inductor design, its my understanding that the Q is relatively low also the amount of variability is fairly limited compared to other designs, but they do work and they are easy to build.

author: ArthurDent
author_rank: Super Contributor
timestamp: January 11, 2019, 02:13:04 am
content: General Radio Co. variable inductors have been around for ages and I have one sitting around somewhere.https://www.radiomuseum.org/images/radio/general_radio/variable_inductor_107_k_1322111.jpg

author: edpalmer42
author_rank: Super Contributor
timestamp: January 11, 2019, 05:00:14 am
content: Suzy, you mentioned a SMPS. Did you find one of these in a SMPS?I've never taken one apart to find out how it was wound, but could this be a common-mode filter choke?Ed

author: ejeffrey
author_rank: Super Contributor
timestamp: January 11, 2019, 05:33:45 am
content: Quote from: SuzyC on January 11, 2019, 01:59:19 amNo, flux cancellation doesn't cause energy loss. Its not like the flux is created and they destroyed, the current path just creates very little flux. Energy will be lost due to the wire resistance of course, and if there is imperfect cancellation then you can get radiation.QuoteSure, it is useful if you want to make a high power 50 ohm load or other RF power resistor. But that's about it.

author: boB
author_rank: Frequent Contributor
timestamp: January 11, 2019, 05:50:13 am
content: Quote from: ejeffrey on January 11, 2019, 05:33:45 amSounds pretty useful to me !

author: Zero999
author_rank: Super Contributor
timestamp: January 11, 2019, 11:05:58 am
content: SuzyC,I'm sure you now realise that the purpose of this winding is to be non-inductive, so the title of the thread is contradictory.Another way to think of this is a transformer with two primary windings connected out of phase. The supply feeding the transformer will just see the DC resistance of the windings connected in parallel. The magnetising fluxes will cancel, so there will be no inductance and the transformer will not work. A large current will flow, causing the fuse or circuit breaker to open.

author: coppercone2
author_rank: Super Contributor
timestamp: January 11, 2019, 02:11:00 pm
content: Quote from: ejeffrey on January 11, 2019, 05:33:45 amI think she is asking about a transient field analysis diagram of such a system.

author: MrAl
author_rank: Super Contributor
timestamp: January 12, 2019, 03:23:51 pm
content: Quote from: SuzyC on January 10, 2019, 11:29:22 pmThe short answer is you will get partial cancelation of the total inductance. You never get total cancelation though because the two windings always occupy different locations in space, and different locations means that the fields do not interact completely.There are calculations you can do on simple structures but as the structure gets more complicated the solution gets more difficult because it involves mutual inductance which involves integration in sometimes several directions.To keep it simple though, when you have two wires each with current flow the mutual inductance depends on the orientation of the wires and distance from each other, and because there are so many different shapes and ways to separate them, the shape is most likely a function and the distance is also a function, so integrating gets a little complicated real fast. Some good books resort to tables for commonly wound structures such as cylindrical coils and coils with triangular and rectangular cross sections, and cross sections that have multiple sides (like a hex for a six sided cross section). The formulas often also neglect certain aspects such as wire diameter but sometimes include that too.If not anything else, it's a really interesting subject area. If you are into calculus, pick up a book.When i first saw the title of this thread i thought it would be about a randomly wound coil which is sometimes used.

author: ebastler
author_rank: Super Contributor
timestamp: January 12, 2019, 03:27:32 pm
content: Quote from: SuzyC on January 11, 2019, 12:20:13 amBecause an "inductor" wound for minimum inductance is pointless?