Fans damaged by neodymium magnets  - Page 1
Forum section: electronics / general

author: SolderSucker
author_rank: Regular Contributor
timestamp: January 11, 2019, 02:50:30 pm
content: I have a couple of small fans that used to work just fine until I accidentally brought some small neodymium magnets near them, whereby they naturally attached. Magnets have now been removed but one fan now won't spin at all, the other spins in a jerky, erratic manner.These fans are used in the Nintendo Switch games console and look like this:https://da2lh5cs8ikqj.cloudfront.net/cart-products/OLXvKfY1GxQ1FFvO.mediumCan anything be done to get the fans working properly again?

author: Kleinstein
author_rank: Super Contributor
timestamp: January 11, 2019, 02:54:49 pm
content: There are 2 possible damages:1) the magnets in the motor.2) the sensor to control the motor. Not sure if the sensor is sensitive - some are, many not.I theory there is a chance to get the magnet back to about the right magnetization, but it is tricky.

author: SolderSucker
author_rank: Regular Contributor
timestamp: January 11, 2019, 03:03:23 pm
content: Thanks, had a feeling there wouldn't be a simple solution.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 11, 2019, 03:10:49 pm
content: Getting the magnetization back would as a first step need a way to know the state one wants to have. So it needs 1 working fan and a way to measure the field. Than it's about applying a strong field of that shape, e.g. with the magents. Removing the magnets could be tricky in not to get a different symmetry when one is magent is missng.

author: SolderSucker
author_rank: Regular Contributor
timestamp: January 11, 2019, 03:21:18 pm
content: Well I have a working fan but no idea how to measure the field.

author: Zero999
author_rank: Super Contributor
timestamp: January 11, 2019, 03:52:00 pm
content: Yes, I suspect the permanent magnets inside the fan have been demagnetised/flipped by the strong neodymium magnet.Unfortunately there's no way of checking without taking the fan to bits. The magnets tend to be very cheap plastic filled with magnetic particles. I doubt there's any easy way of re-magnetising them at home.

author: jimdeane
author_rank: Regular Contributor
timestamp: January 11, 2019, 04:10:00 pm
content: You may have magnetized part of the frame, or even component leads, confusing the hall effect sensor in the fan.I would try demagnetizing with the neodymium magnet (or a cassette tape head demagnetizing wand, if such is in your workshop). With the magnet, bring it close to the fan, probably where it was before, then start rotating it and keep rotating it as you back it away from the motor.I'm not sure the strip magnets are affected much by external fields. I've had fridge magnets near huge nd magnets and still had the appropriate stripe pattern when demonstrating the field viewer for class.

author: Zero999
author_rank: Super Contributor
timestamp: January 11, 2019, 04:30:20 pm
content: Quote from: jimdeane on January 11, 2019, 04:10:00 pmI'd be wary about demagnetising the frame, as there's a risk the permanent magnet rotor could also be demagnetised.How close did the fridge magnets get to the neodymium magnets? I once stuck a fridge magnet to a more powerful neodymium magnet and can tell you that it certainly did alter the magnetisation pattern.

author: dnwheeler
author_rank: Regular Contributor
timestamp: January 11, 2019, 07:09:05 pm
content: It could be as simple as magnets having been pulled out of position, and simply putting them back may solve the problem.

author: amyk
author_rank: Super Contributor
timestamp: January 11, 2019, 10:46:52 pm
content: I suspect it's either the frame or stator laminations that have become magnetised. Remove the rotor and run the rest through a deGaussing coil.

author: SolderSucker
author_rank: Regular Contributor
timestamp: January 12, 2019, 10:13:05 am
content: Quote from: amyk on January 11, 2019, 10:46:52 pmAfraid to say that I don't have a degaussing coil.