Beginner Project: Super Cheap Magnetic Mixer

[wesdoestuff]’s mother needed a clean way to mix together fragrance oils. Being the stand up kinda guy he is, [Wes] threw together a few spare parts to make this Magnetic Stir Plate.

The whole setup is amazingly simple. Pry the fins off of an old computer fan, glue a couple magnets to the fan’s hub. Drill a hole for a DC connector, find some sort of cover and.. Bob’s your uncle! [Wes] advises that you test the spacing of the magnets on the hub before gluing them permanently, as they can be a bit tricky to align.

The stir bar for non food items is  a magnet bar from one of those crazy magnet and ball bearing toys, it is basically just a solid magnet covered in plastic.  Food safe bars can be acquired, though they are not as cheap.  With all that room under the hood we would love to see him throw in some kind of a PWM speed control but that could be a bit complicated. Most of us could throw this together from spare parts.  Video after the jump!


23 thoughts on “Beginner Project: Super Cheap Magnetic Mixer

  1. Using slower motors, the fishing rod building community has been using hacked stir plates for years to mix epoxy.

    Generally built with a steel ball bearing (as the paddle), an AC timing motor, and something to hold your cup still (the viscosity of the epoxy would spin the cup).

  2. I was contemplating this very thing just a few nights ago, and came to the same conclusion of using a computer fan with magnets glued on it.

    I was going to go a little further with the stir-bar though. I have some Alumilite casting resin that I was going to use to coat a small bar magnet or something. Not sure how food-safe Alumilite is though.

  3. Yep, stir plate. Very easy. You can even skip the potentiometer if you find a wall wart that undervolts the fan such that you get the desired speed.

    @andrew, others – don’t try to make cheap metal “food safe” by coating it in silicone. You’ll have so many bubbles and pits that food and bacteria will collect in… you’ll never have a sanitary stir bar. Instead just get a purpose-made stirbar off ebay.

    With these homemade stir plates, I find the 1 to 2 inch stir bars work best.

    Beakers and drinking glasses work well, but most bottles will not as they have convex floors and that makes the stir bar spin off to the side easily.

  4. I’d like to see someone design a stirrer without the extra motor. It’s silly to convert magnetic fields to rotational motion, back to magnetic fields, and back to rotational motion again. With a properly designed electromagnet, it could spin the stirrer bar directly. It would be solid state, and very thin too.

  5. I second Rachel’s idea too…(or is that a third?). Computer fan motors tend to have a single four pin package that handles both driving the motor and sensing rotation speed – maybe someone could salvage that part for use in a solid state stirrer; otherwise inertia and viscosity will mean you will need some smart code, sensors and such to be able to spin up to speed and correct for slow down events if/when the air bubble interacts with the stirrer.


  6. I made one of these when i was in highschool with pretty much the exact same materials except i scrounged some magnets out of an old HDD. Also learned that playing with high strength magenets for long periods of time can make you feel like crap because the magnets can attract the iron in your blood.

  7. @bob I tried this; the position detector can’t detect where the magnet is. The other problem is that even if you fix the sensor problem, the stator cannot exert enough force to move even very strong magnets at anything above a very low speed/torque when that magnet is above the plane of the motor. The stator is designed to exert an EM field in the wrong direction, so the only solutions are either a custom stator or a hacked stator with magnetic material added on to bring the focus of the EM field into the right plane, I think. The latter would probably be easiest, as you could imagine that the relatively thin arms of a pancake stepper stator could be bent upwards, or bolts welded to a cooling fan stator.

    @Fallen good point.


  8. I like the simplicity of this, just about anyone could throw this together in ten minutes!

    You could use this for mixing stuff in a test tube too, just drop a ball bearing or a small magnet in there and hold it over the device.

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