Author Topic: Why stick a magnet to an inductor permanently ?  (Read 8525 times)

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Offline BravoVTopic starter

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Why stick a magnet to an inductor permanently ?
« on: March 04, 2013, 06:12:49 am »


While watching Mike's video on his Applent AT825 LCR teardown & review ->Youtube video @ 30:45, something interested me when Mike did put a permanent magnet on the measured inductor and tweaked the inductor's characteristics by moving the magnet distance. Suddenly I remembered I also have a similar power inductor that I salvaged that has a permanent magnet attached and shrink wrapped at the inductor from the factory. Above photo is Mike's hand holding the measured inductor with the magnets from the video.

Why ?  ???

Attached below the close up photos at the inductor with a screw hanging & stickied at the permanent magnet part on top.
« Last Edit: March 04, 2013, 07:07:37 am by BravoV »
 

Offline Bored@Work

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Re: Why stick a magnet to an inductor permanently ?
« Reply #1 on: March 04, 2013, 06:45:27 am »
I only remember him putting some ferrite material in the coil, which is a totally different game.
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Offline cyr

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Re: Why stick a magnet to an inductor permanently ?
« Reply #2 on: March 04, 2013, 06:57:23 am »
I guess you could do that to offset the magnetic field, so you can use a higher DC current without saturating the core (as long as it's the right polarity).
 

Offline mariush

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Re: Why stick a magnet to an inductor permanently ?
« Reply #3 on: March 04, 2013, 07:04:57 am »
It says in the video, at around 27:00 to alter the quality factor (the higher the q the sharper the resonance) / magnetic field the inductor creates. At 30:44 is exactly the answer to your question.

A toroidal inductor keeps the magnetic field mostly inside the inductor circles and doesn't radiate it outside that much, the normal inductors have a magnetic field that expands.

They probably didn't have room on the board for a toroidal inductor so they went with the normal style inductor but maybe they needed an inductor with low inductance value but high peak current and an inductor with higher inductance was cheaper. So maybe they put a magnet to shrink the field, to lower the quality factor and therefore decrease the inductance value.
 

Offline Rufus

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Re: Why stick a magnet to an inductor permanently ?
« Reply #4 on: March 04, 2013, 09:23:36 pm »
 

Offline nukie

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Re: Why stick a magnet to an inductor permanently ?
« Reply #5 on: March 04, 2013, 10:53:35 pm »
How much heat does it take to weaken the magnet?
 

Offline amyk

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Re: Why stick a magnet to an inductor permanently ?
« Reply #6 on: March 05, 2013, 12:30:58 pm »
How much heat does it take to weaken the magnet?
Depends on the magnet's Curie temperature.
 

Offline BravoVTopic starter

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Re: Why stick a magnet to an inductor permanently ?
« Reply #7 on: March 06, 2013, 06:24:16 am »
Thanks for the replies, and also the link provided by Rufus !  :-+  (to be honest, I had quite a headache reading that patent paper  ;D)

So .. the final conclusion is that they made this purely for a "quick & cheap" way to increase the inductor's saturation current ? (within the anticipated lowered inductance and Q of course)

Is that all ?  :-//


How much heat does it take to weaken the magnet?
Depends on the magnet's Curie temperature.

Looking at the shrinked wrapper which is just a plastic, I don't think the inductor is designed to run near the magnet's curie temp.
« Last Edit: March 06, 2013, 06:30:37 am by BravoV »
 

Offline BravoVTopic starter

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Re: Why stick a magnet to an inductor permanently ?
« Reply #8 on: March 12, 2013, 11:22:02 am »
So .. the final conclusion is that they made this purely for a "quick & cheap" way to increase the inductor's saturation current ? (within the anticipated lowered inductance and Q of course)

Is that all ?  :-//

Shameless and final bump begging for clarification on the conclusion.  :P


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