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I am trying to build my own generator at home for fun, I saw on a video in youtube https://www.youtube.com/watch?v=YsSm65DAcCg where the guy placed smaller magnets in between the main magnets of the rotor (at around the 10 minute mark). I was wondering if whomever has seen this done before, if it is actually helpful, especially since I am looking to use this as a generator and not as a motor. I would imagine it skews the magnetic lines to one side, but I am not sure. Any help would be appreciated before I buy magnets. Thanks.

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    \$\begingroup\$ Doesn't he explain it thoroughly enough in the video? If you've somehow missed it, then it's a circular Halbach array. \$\endgroup\$ Sep 30 '18 at 16:42
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    \$\begingroup\$ If it was to reduce commutation arcing then it's likely it is for the same reason that interpoles are used in a generator. \$\endgroup\$
    – Andy aka
    Sep 30 '18 at 17:19
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    \$\begingroup\$ Oh wow this is incredibly useful. I have a homemade 8 pole generator that I suspect has weak field penetration on the inside and severe cogging. Just might have to try a 6 pole Halbach array! \$\endgroup\$
    – K H
    Oct 1 '18 at 1:04
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This is more or less just transferred from Wikipedia, however:

As @HarrySvensson indicates, this is a Halbach array, apparently used to create a magnetic field that is stronger on one side than the other. Images from wikipedia:

Linear Halbach Array image from wikipedia

So you can see that when they are arranged this way, the magnets create strong wide poles on one side and alternating narrow poles on the other side to cancel each other out. The field generated looks like this:(Also from wikipedia)

Used in a generator, this creates a stronger field on the inside for power generation and a weaker field on the outside to minimize the mass of silicon steel needed to confine the magnetic path.

Edit: Having tried to configure magnets into this arrangement I will note that strong rare earth magnets strongly disagree with being placed together this way! a strong mechanical setting and retention mechanism is necessary in order to use this type of array!

Halbach Array FEMM diagram

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