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Inductor Polarity??
Inductor Polarity??
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Old 7th July 2012, 04:39 AM   #1
Zero Cool is offline Zero Cool  United States
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Default Inductor Polarity??

Ok I know that sounds like a silly question, but is it?

Some high quality film caps are marked with an "In" and "Out" lead marked on which lead is connected to the inner or outer part of the cap.

and while I was looking as some foil inductors It dawned on me that maybe they have a "preferred" direction related to signal flow as well?? Would we want the "In" to enter from the inside of the inductor and exit out the outer part? or the reverse?

ZC <---over thinking things once again!
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Old 7th July 2012, 08:53 AM   #2
RJM1 is offline RJM1  United States
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No polarity.
For example, if you have a 60Hz signal across the inductor wouldn’t your input and output swap 60 times a second?

Last edited by RJM1; 7th July 2012 at 08:58 AM.
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Old 7th July 2012, 11:06 AM   #3
davidsrsb is offline davidsrsb  Malaysia
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A layer wound inductor might have different strays to ground from either terminal, so at RF there could be some asymmetry
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Old 7th July 2012, 01:24 PM   #4
zigzagflux is offline zigzagflux  United States
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Sure, every inductor has a polarity. For audio, I doubt it carries any meaning other than the interaction between coils in proximity to one another. The fields can buck or boost with one another with the same excitation. Again with music content with its various phase shifts of sine waves, I doubt it is of any practical effect- just keep spacing and orientation per the recommendation of other threads.
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Old 7th July 2012, 06:41 PM   #5
DF96 is offline DF96  England
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Caps are marked so that the outer can be connected to the lower impedance end in order to minimise electrostatic pickup. In many cases it doesn't matter anyway. A similar effect might possibly happen with an inductor.

Inductors also have a real polarity as, for example, a solenoid can be right or left-handed. This changes the polarity of induced voltages from elsewhere, and the polarity of the external magnetic field. Swapping ends does not change this (think about it!).
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Old 7th July 2012, 06:49 PM   #6
KatieandDad is offline KatieandDad  United Kingdom
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At AF it makes no difference unless they have a DC component or are in close proximity to each other.

At RF the air is acting like a transformer.
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Old 7th July 2012, 09:53 PM   #7
Jay is offline Jay  Indonesia
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I can hear the difference. Most of the time you will want the outer coil to be the input and the inner coil to be the output. I notice that switching power supply consistently do the same for input coil filter, may be for a reason.
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Old 9th July 2012, 04:51 AM   #8
rabbitz is offline rabbitz  Australia
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From an Australian speaker manufacturer and kit supplier, signal in to inner winding.

Probably doesn't matter but if it bothers you, just use the same for both speakers.
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Old 21st October 2019, 07:01 AM   #9
DBruce is offline DBruce
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Current inductors do have polarity issues.

Imagine a spiral copper wire and two free electrons are put at the center tip of the spiral, the two electrons will expel each other and try to keep away from each other as far as possible, finally they will stay at the most outer ring of the spiral, apart from each other at the two most distant points in the spiral they can find.

Since it is the free electrons that carry the current in copper wires, that means the negative electrons have a tendency to flow from inner round to outer in a conventional spiral coil, which means it is easier for the positive current to flow from the outer round to the inner. So which side of the coil (inner or outer) would you call it the positive?

Most music we heard are asymmetrical signals, piano strikes a string so its first wave of sound has a positive sound pressure to our ears, drums are the same. Human voice is generated by pushing air out of lungs, that is also asymmetrical and has a positive sound pressure for the first wave. So you see it must be carefully handled from the picking-up mic to the speaker driver, any mistake would make the first output sound wave become negative sound pressure, and that is definitely not fidelity. And asymmetry is very important for us to distinguish a sound, and so is asymmetrical distortions. Yet some people cannot hear the difference but some people can.

Now back to the polarity of the coils, as we can see now an inductor do have polarity issues as long as it is wound with asymmetrical inner and outer rounds. Unfortunately the most expensive foil coils have the most severe inner and outer round problems because they are perfect spiral coils. Multi-layer wire wound coils also have asymmetrical inner and outer round problems. Iron core coils have fewer rounds and sometimes they have only one layer of wires that makes them polarity-free, but they have another severe issue of hysteresis to overcome.

What would it be like for a coil to have polarity that generates asymmetrical distortions? I don't know. But here is a video showing a person messing around a drum signal with various asymmetrical distortions, it might give you an idea about what it would sound like:


So I would say, in a microscopic view, the coils currently available in the market all have polarity issues as long as they are asymmetrically multi-layered, and asymmetrical distortions are definitely there.
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Old 21st October 2019, 08:35 AM   #10
schiirrn is offline schiirrn  Germany
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The voltage potential difference between windings increases from inside to outside as resistance per turn increases. Unless you enter hf territory this doesn't matter.
Preferred BSC? Just using a wide enough baffle.
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