I've made 2 magnetic stirrers for myself now. They're easy to make and work pretty well (though it does take a fair bit of time to put together). You can set your juice to mixing and just walk away to measure out a new batch. If you're handy and like to tinker, its a really fun project. I learned quite a bit about working with electricity and wiring from this project.

I think all told, each mixer costs me roughly 15$ to make, and probably about 3-4 hours of labor and tinkering.

All you really need is:

• a computer fan
• a power supply
• a dc motor controller, with potentiometer (potentiometer is just a dial that lets you adjust spin speed)
• 2-4 small magnets
• magnetic sir bar (buy a variety pack: size of the stir bar makes a big difference: too small won't stir well, too big won't spin at all. You'll want a few different sizes at least)
• a box
• scrap wood, couple nails / screws, glue or other adhesive

Edit: you'll probably also want some kind of beaker or flask large enough for the whole batch, so you can mix before you bottle. You can find these at many vape suppliers, nic river and nude nictone both have some available.

Fan: Pretty much any generic tower fan works, but very small fans might have trouble turning the magnet bar smoothly.

Power Supply: You need a power supply that provides the same # of Volts your fan requires, and at least as many amps as the fan needs. If my fan says 12v / .5amps, I'll need a supply that provides exactly 12v and at least .5 amps. (Most tower fans I've seen run 12v and .1-.5 amps. A 12v / 1amp power supply will probably work with almost any pc fan.)

Controller This is the dc motor controller that I've used in both my mixers. They work well and they're not super expensive (~$8.50)

Magnets You can use pretty much any magnets. Simply glue your magnets onto the middle of the fan (make sure you have one positive side and one negative side facing up, so the stir bar holds at both ends.) For my first mixer, I removed a magnet from a hard drive, and supplemented it with a magnet bar I had from an old name tag. For the second mixer, I just bought some circular neodymium magnets from home depot; they were only a few $ and saved me a lot of time breaking open the HDD.

Box I used a small plastic box from home depot's storage solutions section. Cost about 3$.

Ps: Or there's always my old solution: put 2-3 bottles in a sock, and swing it around like a sling. 45 seconds of that is usually more than enough.