Why stick a magnet to an inductor permanently ? - Page 1
Forum section: electronics / beginners

author: BravoV
author_rank: Super Contributor
timestamp: March 04, 2013, 06:12:49 am
content: 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.

author: Bored@Work
author_rank: Super Contributor
timestamp: March 04, 2013, 06:45:27 am
content: I only remember him putting some ferrite material in the coil, which is a totally different game.

author: cyr
author_rank: Frequent Contributor
timestamp: March 04, 2013, 06:57:23 am
content: 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).

author: mariush
author_rank: Super Contributor
timestamp: March 04, 2013, 07:04:57 am
content: 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.

author: Rufus
author_rank: Super Contributor
timestamp: March 04, 2013, 09:23:36 pm
content: Patent for ithttp://www.google.com/patents/US6710693

author: nukie
author_rank: Frequent Contributor
timestamp: March 04, 2013, 10:53:35 pm
content: How much heat does it take to weaken the magnet?

author: amyk
author_rank: Super Contributor
timestamp: March 05, 2013, 12:30:58 pm
content: Quote from: nukie on March 04, 2013, 10:53:35 pmDepends on the magnet's Curie temperature.

author: BravoV
author_rank: Super Contributor
timestamp: March 06, 2013, 06:24:16 am
content: Thanks for the replies, and also the link provided by Rufus !(to be honest, I had quite a headache reading that patent paper)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 ?Quote from: amyk on March 05, 2013, 12:30:58 pmLooking 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.

author: BravoV
author_rank: Super Contributor
timestamp: March 12, 2013, 11:22:02 am
content: Quote from: BravoV on March 06, 2013, 06:24:16 amShameless and final bump begging for clarification on the conclusion.