Author Topic: Air cored inductors proximity to conductive objects  (Read 422 times)

Offline John123

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Air cored inductors proximity to conductive objects
« on: November 23, 2022, 01:10:17 AM »
Can air cored inductors be influenced by proximity to other conductive things such as heatsinks even if nothing actually enters the inside of the windings? I'm talking about simple ones such as this:

Online davekni

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Re: Air cored inductors proximity to conductive objects
« Reply #1 on: November 23, 2022, 04:44:20 AM »
Quote
Can air cored inductors be influenced by proximity to other conductive things such as heatsinks even if nothing actually enters the inside of the windings? I'm talking about simple ones such as this:
Yes, but much less so than similar ferrite-core inductors.  With air-core, most of the magnetic reluctance is where field is concentrated through core center.  With lots of area for field to return outside of the coil, blocking some of that return path has only a tiny effect.  Unless you block much of it, such as if you milled a slot in a heatsink and placed it over the coil blocking most field return paths.
David Knierim

Offline Twospoons

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Re: Air cored inductors proximity to conductive objects
« Reply #2 on: November 23, 2022, 09:29:01 AM »
It would be very dependent on the aspect ratio of the coil - long skinny vs wide flat.  This is how basic metal detectors work, after all, by using a wide flat coil.

Offline John123

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Re: Air cored inductors proximity to conductive objects
« Reply #3 on: November 23, 2022, 11:27:18 PM »
Quote
Can air cored inductors be influenced by proximity to other conductive things such as heatsinks even if nothing actually enters the inside of the windings? I'm talking about simple ones such as this:
Yes, but much less so than similar ferrite-core inductors.  With air-core, most of the magnetic reluctance is where field is concentrated through core center.  With lots of area for field to return outside of the coil, blocking some of that return path has only a tiny effect.  Unless you block much of it, such as if you milled a slot in a heatsink and placed it over the coil blocking most field return paths.
Thanks Dave, here's some photos of it. Excuse the messy amateur DIY construction.


It would be very dependent on the aspect ratio of the coil - long skinny vs wide flat.  This is how basic metal detectors work, after all, by using a wide flat coil.
It's a single layer coil measuring 32.5mm x 15mm and about 26 turns of litz wire (was aiming for a couple uH). It's 12mm at its closest point from the grounded heatsink. Flying blue wire is circuit ground.
« Last Edit: November 23, 2022, 11:30:29 PM by John123 »

Online davekni

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Re: Air cored inductors proximity to conductive objects
« Reply #4 on: November 24, 2022, 03:02:11 AM »
Looks fine.  Heat sink should have negligible effect on inductance of coil with that geometry.
David Knierim

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Re: Air cored inductors proximity to conductive objects
« Reply #4 on: November 24, 2022, 03:02:11 AM »

 


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