Simple DIY Magnetic Stirrer




This instructables is to show how to build your own magnetic stirrer from parts you may have at home.

This one was built to mix E-cigarette vape juice. You could use it to stir almost any liquids, so it can be used for mixing vape juice, mixing for cooking, or in a chemistry lab.

About 30 minutes

Tools required:
Screw driver
Drill and drill bits
diagonal cutters or strong scissors
[optional] soldering iron and solder
[optional] adjustable crescent wrench

Parts required:
Project box (some sort of container)
12VDC Computer case fan
12VDC power supply
16 gauge wire
SPST switch (optionally illuminated)
Potentiometer and knob
Flea/mixer bar
Superglue (or other strong contact adhesive)
Hard drive magnet
Female blade connectors (as needed)
Wire nut (as needed)
[optional] Rubber feet (so the box doesn't walk)
[optional] Fuse (safety says always use a fuse!)

Possible parts sources:

Almost all of this is out of my junk box.

Box - anything square(ish) and preferably plastic in case something comes loose. I used a 8x6x3" Radio Shack project box, which costs $9.

12VDC computer fan. That is a fan from a donated (junk) computer. You can use a case fan or power supply fan. The power requirements should be marked. The one shown is a Cooler Master PL12S12L, 12VDC 0.13A that spins at 2000 RPM. Similar fans at TigerDirect can cost about $10.

12VDC power supply. It must output more than the rating of the fan. I found this one in my junk box. It's 12VDC 1.2A. If you don't have one, ask around. Any respectable geek has a box full of these. If you can't find one, they can be bought for about $15.

16 gauge wire. You can grab this from anywhere. I prefer to color code so I don't get confused. Worst case, you can use part of the wire from the power supply.
Red = positive
Black = negative
Blue = special (negative for switch light)

SPST switch. It can be almost any switch, as long as it's rated for 12V and at least the amps of the power supply. This one uses a round hole and has a nut, which is simpler to install. You can use a small automotive switch, or a power switch from something else (like a power supply). This switch is rated for 12V @ 30A from RadioShack and would cost $4.49. If you buy a switch, make sure it doesn't say "momentary", unless you want to hold the button the whole time it's running. You can use other switches (SPDP, DPDP, etc). They just have extra poles you won't use

Rheostat/Potentiometer and knob. This is to be able to adjust the speed. You can source this from almost anything with a knob (volume knob, tuner, etc), as long as it can handle the power. The knob is optional, but looks better. This is a 25 ohm, 3watt rheostat from Radio Shack that costs $4.49. For this fan, we need to handle 1.56W Volts * Amps = Watts , so 12V * 0.16A = 1.56W . You can probably find a better potentiometer and use resistors as needed to get other speeds.

Stir Bar / Flea. This is the little white thing that spins. I couldn't find any locally. We got a 7 pack for $8 on Amazon. I recommend a variety of sizes. The size of the flea is significant to how fast the mixture spins. I used a fairly large one for the demonstration videos.

Hard drive magnet (or neodymium magnets bar magnet from the hardware store). To extract it from a hard drive will be a little (fun) work. Hard drives use Phillips, Torx, or Security Torx screws. There's always one (or more) under a sticker Sometimes it's faster/easier/more fun to use a hammer and chisel. You're going to destroy the drive anyways. The two magnets are on the back part of the arm. They are going to be difficult to separate. You can't pull them apart, but you can twist and slide them apart by hand. Don't get your fingers between them.

Connectors, fuse, feet. most people have these in their junk box. If not, you can get them cheap from auto parts stores, home improvement stores, or Radio Shack. Or ask your friends.

If you buy everything new, it will cost you around $50, which is cheaper than a commercial magnetic stirrer would cost. In my case, it was $8 because I had the rest of it laying around.

This instructable assumes you know something about basic electronics. I won't go into detail about how to solder or make connections. For what we're doing, it's very simple. You'll notice I used both connectors and solder. That's up to whoever builds it.

Disclaimer: By reading and/or using these instructions, you take on all liability for anything that may happen.

Step 1: Layout

Think about where you want all the parts when you're done, and make sure things fit. This is a simple step, but people always forget.

You want to put the fan in the middle of the top, so you can center whatever is being stirred.

I chose to put the knob in the middle of the front, and offset the power switch to the right, with the wiring on the right. You can do it any way you want. I recommend both the power switch and knob are both on the front for easy access.

Make sure the chosen fan can spin freely with the magnet on. You can just lay the magnet on the cover and try to spin the fan. If it doesn't, you may need to use washer as spacers. There's usually a bit of a gap, so you should be fine.

Make sure your fan won't hit the back of the potentiometer or switch, and that you can secure the wires safely away.

Step 2: Mechanical Assembly

Now that you've decided where you want everything, it's time to play with power tools!
(Kids, ask your parents to do it. They love playing with power tools!)
You want to be careful doing this step, so everything looks good.

  1. Drill the appropriately sized holes for your potentiometer, power switch, and a hole in the back just large enough to slide the power cord (without the plug) in.
  2. Mount (but do not wire) the potentiometer and power switch
  3. Carefully center the fan on the top, and mark your four mounting holes. Drill 4 holes just large enough for the 4 screws to go in.
  4. Take the hard drive magnet, and try to center it as best as you can on the fan. You'll want the magnet facing away from the fan. Use superglue to attach the metal side of the magnet to the fan. Do not otherwise modify the fan. You do not want to do other modifications to the fan.
  5. Mount the fan to the top with the appropriate screws.
  6. [optional] put rubber feet on the box. This is a good idea so it won't make too much noise, or "walk".

Step 3: Electrical Connections

Reference the provided diagram.

  1. Cut the connector off the power cord. This will save you hours of trying to find the right socket.
  2. Put the power cord through the hole in the back of the box, and tie a knot in it so it won't pull back through.
  3. Verify the positive and negative power supply wires with your multimeter. I like to tie a knot in the positive wire for easy identification. You'll notice that in the previous photo.
  4. [optional] put a fuse at the end of the positive wire. The next step will connect to the other side of the fuse.
  5. Connect the positive wire to the appropriate pole of the switch (bottom on mine)
  6. Connect a wire from the appropriate pole of the switch (center) to the center pole of the potentiometer.
  7. Verify the rotation of the knob with the ohm/resistance setting of your multimeter. When turning the knob to the right, the resistance between the center and one pole should drop.

  8. Connect the appropriate pole of the potentiometer to the positive (yellow if present, or red).
  9. Connect the negative power supply wire to the black wire of the fan.
  10. [optional] If you are using an illuminated switch, you will need to make a connection from the appropriate pole on the switch (top) to the negative power supply wire.
  11. You can test your electrical work now. Plug it in, hit the power switch, and see if the fan spins.

    Soldering, wire shrink, blade connectors, and/or wire nuts are all your choice. I chose based on the physical connections.

Step 4: Button It Up

At this point, you should have all of the physical and electrical connections made and tightened. Double check them.

If you are sure you are complete, make the necessary physical attachments.

You can now test it with a flea to see it spin. You don't want to do this for very long, so you don't risk wearing the coating.

Step 5: Try It Out (First Demonstration)

This demonstration mixes oil and water. They don't normally mix. As you can see in the video, it mixes very well.

For this demonstration, I used a fairly large flea, because of the thickness of the oil and the total volume. As you will see in the video, the vortex does not pull all the way to the flea, so it doesn't aerate the mixture. That is usually desirable.

If you are using a thin fluid or a smaller volume, you may want to use a smaller flea.

Step 6: Second Demonstration

This demonstration show a smaller volume of water with dish soap in it. This is easier to see the mixing with.

I used a flea that was a bit too large for the viscosity and volume, so it did aerate the water. This can be desirable in some circumstances.



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29 Discussions

Captain Simion

4 years ago on Step 6

Good job - a very neat device! We use this type of equipment in Chemistry labs for the same types of jobs, and the largest long-term problem is spilling things into the mechanism. What if you mounted the fan in the "bottom" of the plastic box, and the feet on the aluminum plate, so a spill run down the outside of the plastic and stay outside of the box? Just turn it upside down.

2 replies
rpotts2Captain Simion

Reply 2 years ago

This whole thing (except for the fan itself) could be built so that all electrical components are away from the box and reduce the chance of liquids spilling in. Or, you could just get marine-grade parts and a tube of silicone caulk.


That's one of the nice things about doing it yourself, you can built it to suit your needs. :) Spillage shouldn't be a problem in this one, but yes you could assemble it with the box upside down. I just chose this way ... well ... pretty much on a whim.


3 years ago on Introduction

in fact using potantiometer for controling fan speed is wrong!

the correct way is using PWM.

2 replies

Reply 3 years ago

the fan is a brushless motor so to vary it needs a lower voltage


Reply 3 years ago on Introduction

You can use either method. It's just a DC motor. You're not driving circuitry inside. A potentiometer is a bit easier and cheaper than a PWM controller.

Dr. Solomon

4 years ago

Great instructable. I had been thinking of making a mag stirrer and this approach is elegant and effective!

1 reply

4 years ago on Introduction

Nice project! I'd have made one of these if I didn't already buy a small mag stirrer for my kitchen. And for those asking about uses, I use mine as a cocktail stirrer. :) If I decide I need a second one, I'll try this route.

1 reply

Reply 4 years ago on Introduction

Thanks. :) And ya, that sounds like a great way to make drinks. I'll have to try it.


4 years ago on Introduction

This is pretty cool - I can see this being used for Homebrewers when they need to make yeast starter batches - maybe brew companies sell a vibrating stand that swirls the yeast and the malt solution to double the yeast for big beers. This could do the same! I would need to check on the swirling speed versus this device...


4 years ago on Introduction

I used to work in research labs and always wanted one of these things for home - but though you say you can use it for cooking, I don't see how you could use one *as* you're cooking - a glass container would be okay (if it's flameproof) but how would you use the stirring gizmo? (I won't be making one of these, I'm just intrigued by how you use it to cook.)

5 replies

Reply 4 years ago on Introduction

heh, no not as you're cooking. It's the mixing stage. :)

For the E-cigarette people, they don't "cook", they just mix flavors together, and they need to mix them a lot.

But, you could do something weird like make scrambled eggs with it. Well, overly scrambled eggs. Throw an egg in, and let it run. When it's scrambled, remove the flea and pour it in the pan.

I haven't actually tried to make eggs with it, that's just an example. But now I think next time I want scrambled eggs I'll try it, and post the video. :)


Reply 4 years ago on Introduction

"The flea"? Heh heh that must be a professional cooks' technical term. Well, if ever I need to stir something a LOT I'll remember this and see about coming back for the instructions. Thanks!


Reply 4 years ago on Introduction

Actually, "flea" is what my teacher in high school chemistry called it. It just stuck with me. Wikipedia has a mention of the origin of the name. I've also heard it called "pill", probably because that's what some look like.

I just checked Amazon, and it seems a lot of vendors have that in the title, so I can't be the only one who calls it that. :)


Reply 4 years ago on Introduction

Aha! I see - you're talking about the stirrer-thingy! I thought you meant the scrambled eggs! LOL my mistake.


Reply 4 years ago on Introduction

Heh, I didn't even realize I wrote "cooking". I just edited the text to be a bit clearer. Just for fun, I think I'm going to make scrambled eggs with it in the morning. :)


4 years ago on Step 2

why do you not want to otherwise modify the fan? It shouldn't need the blades for cooling and they are only slowing it down/wasting power.