Welcome back, I know it’s been awhile! Hope everyone had a happy new years.
I purchased an additional magnetic phone mount, and was thoroughly underwhelmed. The piece that holds the magnetic disk has a very short rotational range before it releases, and I found it coming off with my phone whenever I removed it. As the tinkering homebrewer I am, I thought to myself, "Hmmm... I wonder if I can modify this and use it for brewing?". The desire is not a new one, it's very similar in function, and design to the Stir Plate Magnet Mounting-Thingy! from homebrewfinds.
Tl;dr Yes, it makes a very simple premade magnet holder.
While I'm confident different models and styles will be usable, I have only tried with this one particular model. They're likely produced in mass and rebranded for different companies, just find out if the piece being used is attached via a screw or via another method. Other models may need to be cut off or otherwise modified. Moreover, there's almost always a sale on these for $4-$5 each.
Take the backplate off, which is attached via a single screw.
Remove the plastic/silicone/rubber shell that’s covering the four magnets and the metal disk.
Right now the magnets all have their magnetic field pointing in the same direction, upwards. You want to flip two of them over that are on the same side, this will align the magnetic fields in the desired way, and hold the stir bar in place. Some may benefit from removing two of the magnets all together, and leaving two magnets that are anti-parallel. This may improve stirbar stability for some, but my stir plate did not need it. Reassamble the phone mount, and place the stirbar atop. It should center itself and spin with the magnetic disk. Now place the disk onto a fan, and adhere via desired method. I use tape for testing and switch to hot glue when permanent. It should be very easy as they're nearly the same diameter as a fans center surface. There should be no wobble when centered.
The main downside is the strength of the included magnets, but these should be easy to replace if needed for a larger 5L starter. Mine is able to maintain a sufficient dimple vortex, but ymmv with the fans rpm, as well as the supplied voltage.
I promise at some point I'll actually blog about beer, and not just brewing nerd stuff, maybe, eventually. AUKEY Cell Phone Mount model HD-C13