Introduction: Magnetic Stirrer

Picture of Magnetic Stirrer

This instructable shows us how to make a magnetic stirrer, that can be used in your home lab, from the following items:

An old 3" PC fan
A dead hardrive
A 12v ac adaptor
A paperclip


Hotglue gun
Misc Items depending on your taste for getting things done :)

Read on, and enjoy.
Not my original IDEA

Step 1: Set Up Your PC Fan.

Picture of Set Up Your PC Fan.

Find your self a working PC fan.

I used a 3" fan that I salvaged from an old PC I had laying around

1. Pull the black end off of the cables.
2. I did this carefully to keep the metal contacts in place, otherwise you'll be working with bare cables.
3. Optional : Clean the fan of all dust, I did this with a Q-Tip soaked in alcohol, just to make it look pretty :)

Step 2: Connect Power Supply

Picture of Connect Power Supply

Here you'll want to find a 12v AC adaptor

MAKE SURE ITS 12 VOLTS OUTPUT! or else you'll burn out your fan before you even get to test it out.

I used regular tape, just to keep it simple.

1. Put the red cable inside the little socket, this is your positive.
2. Put the black cable on the outside of the plug, this is your negative.
3. Grab your tape and tape these connectors nice and tight so it doesn't shift during use.
4. After the connecters are taped, give it a little tug to make sure they'll stay in place.
5. Plug in adaptor to the wall, and make sure it works.
6. Now unplug your power, and secure the wires to the fan. I used a hot glue gun and put a couple drops to hold the cables down.


Step 3: Salvage the Magnet.

Picture of Salvage the Magnet.

Sorry I dont have pictures for the steps on how to extract the magnets.

1. Get the old harddrive and remove the screws from the casing.
2. Locate the magnets and unscrew them from the casing.
3. Use pliers to hold the piece of metal attached to the magnet, the magnets have some kind of glue holding them down, adding to amazing strength these little things have.
4. What you want to do is bend in two directions so that the magnet comes off the base.

Step 4: Position Your Magnet.

Picture of Position Your Magnet.

Now you are going to position your magnet

1. Place your magnet on the center of your fan.
2. Plug in your fan. BECAREFUL if you didnt position it right you have a high risk of it flying out.
3. If it wobbles, reposition, repeat.
4. After you are satisfied with your magnets position, trace the outline of the magnet onto your fan.
5. Glue it down and repostion your magnet.


Step 5: Housing for Your Fan.

Picture of Housing for Your Fan.

This is where you can get crafty.

I used the fan guard that the fan was in when I removed it from the PC
You can fashion one out of a wooden base, and a CD cover for the top of the fan.

My guard had little waves on the top, I got my rotary tool and evened it out.
Then I put my fan inside and secured it with some more hot glue.

Step 6: Making a Stir Bar

Picture of Making a Stir Bar

This is what will go inside your container that will spin the fluids.

I had a broken CD-ROM laying around, so I decided to take it apart and see what I can get from it.
I found that the little platform that the disc sits in had a metal bar in the center, so I took that out.

You can make it from a paper clip, or any other thick wire.

I found that anything larger than one inch wont work too well, anything smaller, and it wont mix at all.

Experiment with different sizes, what ever fits your needs/likes. I also found that the longer the bar is, the more it will rattle and make ALOT of noise.

Step 7: Put It to Use!

Picture of Put It to Use!

And now you are done!

To test it out, find a jar or cup and fill it with water, then drop your stir bar in it.
Plug it in and watch it work!

Step 8: Improvements

You can add a switch to turn this on and off instead of having to plug it in or out.


evenstill (author)2008-04-02

HELP! I do no understand what I’m doing wrong. I built two of these (cutting off the fan blades) and tested them using 0.5, 1, 2, 3, & 4 cups of water with 0.5, 0.75, 1, 1.24, & 1.5 inch screws. I have two 12 v ac adapters (one is 300 mA and the other is something like 1667 mA). I have used several different kinds of jars (mason style), some with flat bottoms and some with a slight incline in the middle of the bottom. The flat bottomed ones seem to work best. Sometimes it works with the smaller amounts of water (and screws 0.75 – 1 inch long) but sometimes nothing works at all. I plug them in and they work fine for about 2 - 3 seconds then the screw suddenly slows way down while the magnet sounds like it speeds up. Does it have something to do with the water resistance or something? It also seems like the 300 mA adapter spins the fan faster. Anyway, any help would be greatly appreciated. Thanks.

keeboudidoz (author)evenstill2015-05-14

Surely you'd want 12V DC adapters no AC

alwinovich (author)evenstill2008-07-24

sounds like the screw can't "catch up" with the magnet(the fan goes too fast to get a grip on the screw)

macwhiz (author)2008-05-31

you can also use a 24 volt adapter

alwinovich (author)macwhiz2008-07-24

maybe, but I will not guarantee that it works for more then 5 seconds(goes 2x the normal speed but overheats)

macwhiz (author)alwinovich2008-08-03

I've used 24 volt adapters on all of my computer fans rated 12vdc

keeboudidoz (author)macwhiz2015-05-14


wbdotcom (author)2013-07-01

When I place the hard drive magnet in the center of the fan, the fan no longer rotates when plugged in. I have 3 different computer fans that this happens with (all 3" 12V fans that draw at least 150 mA). Are the magnets too strong and interfering with the motor, or is the fan torque not high enough? Thanks

3101 (author)2011-09-15

What makes you think there are magnets in all hard drives. I have opened up several of them and can guarantee there are NO MAGNETS in them !! Perhaps electromagnets but NOT permanent magnets. Can't see why a hard drive would have any permanent magnets at all. What types of apparently rare hard drives did you find any magnets in them ?

stringstretcher (author)31012011-09-21

There is (in every hard drive I have opened... a gob) a very strong permanent magnet attatched to the read/write head. It is a device called a galvanometer, and it is used to position the head over the disc. Google how to salvage a hard drive magnet and you should find something that helps you!

3101 (author)stringstretcher2011-09-27

ok seems i have found one but not 3 as someone mentioned in every hardrive. Also it is very difficult to get into the hardrive as the screws or rivets or like 'star' are not for regular nor philips screwdriver so have to rip them apart

gardoglee (author)31012013-03-03

Torx head screws.

ccorvinus (author)2011-12-08

I have black, read and yellow wires coming from my fan. What should I do with the yellow wire?

3101 (author)2011-09-27

actually those fan motors are rather poorly adapted for this sort of thing because of the low torque. What is better is a series wound electric motor which is
more constant speed and variable torque as necessary like for example in a variable speed drill motor.

fr05ty911 (author)2009-10-03

do you have to use the magnet out of a hard drive or can it just be any magnet??

Eirinn (author)fr05ty9112010-05-03

Don't know if you need the info any more, but any magnet should work - i think he's using the HD magnet because it's free and because the shape might help :)

beehard44 (author)Eirinn2010-10-26

the shape can be bar or something like the HDD magnet, it's just that the HDD magnets are neodymium

jenR (author)2010-01-18

 I found the root of the problem, the magnet I salvaged from an old HD wasn't strong enough. I now use two strong ring-magnets and I can go to full speed with my largest stirrer bar in any jar!

jenR (author)2010-01-10

 I repositioned the magnet once more, and now it doesn't spin out of control anymore. The position of the magnet seems to be very important! 
Another important thing is the bowl you use, it has to have a flat bottom!

Mine works perfect now in water, but when I try a more honey-like liquid, it spins out of control very fast :(

jenR (author)2010-01-09

 I used this instructable to make my own magnetic stirrer. I used a 4.7inch (120mm) computer fan that has three speeds (it's supposed to be 1200,1600 and 2000rpm, but I doubt that).
I collected a hard drive battery and positioned it in the middle (hard to check if it's really the middle). 
I bought 2 real magnetic stirrer bars (0.8inch and 1.5inch) in the local pharmacy. It spins okay on 1200rpm, but then I don't get a vortex. When I try a bigger speed, the bar spins out of control and jumps to the side of my jar and stays there... Did someone encounter this problem too? I tried to reposition the magnet several times, but that didn't help.

sci4me (author)2009-09-21

I want to build it, its just that I need a fan.

steed1172 (author)2009-06-25

can i use any shape magnet??

nickdisney (author)2007-12-05

what am i doing wrong? i have two hard drive magnets on a two inch fan on a 12v computer power supply. my bar is a piece of a steel nail about one inch long. i place it on an aluminum plate and the plate over the spinning fan, and nothing happens. it rattles around a bitbut doesnt spin at all. SOMEBODY PLEASE GET BACK TO ME ASAP!

kikiclint (author)nickdisney2009-05-14

In chemistry class, if the stirrer is going too fast, the stirrer bar ends up just rattling until the speed is slowed down enough. A stronger stirrer magnet, or closer proximity to the stir bar will help. If not, Try to make it slower by either lowering the voltage or use a pulse width to control the fan speed.

Cat on my Lap (author)nickdisney2007-12-16

One major issue with this set up is that Aluminum (at normal temperatures) is non-magnetic and will strongly interfere with the magnetic fields. Try getting the magnets aligned before turning on the fan; though some fan speeds just plain won't work. Is the stir bar actually in liquid or a separate container?

nickdisney (author)Cat on my Lap2007-12-17

well, i haven,t tried it in liquid yet. i dont see how it would be and different. correct me if i'm wrong... Ive also tried putting the nail on a plexiglass sheet, and still nothing. this is going to be a christmas present, so i need as many troubleshooters as possible ASAP. thanks yall...

alwinovich (author)nickdisney2008-08-21

if it's rattling it means that the fan speed/magnetic field strength ratio is not correct try 1bringing the stirrer closer 2use a adapter with less voltage

Cat on my Lap (author)nickdisney2007-12-20

Try just holding the stirrer over the rotating magnet and see if you can feel the pull or "twitch" from the interactions of the magnetic field. Try to keep the magnets as close together as possible without causing them to directly contact each other. The water will help lubricate the stir bar in rotation, plus it'd be good to know if the device will actually stir the liquid (presumably water) in question. Try just using a small bar magnet glued to the fan instead of a hard drive's magnet, it may work better.

alwinovich (author)nickdisney2008-07-24

the magnetic field is blocked by the alu. plate,search lenz's law

zygo91 (author)2009-05-08

Another way that helps remove (although I don't know if its safe) is to get a lighter and apply some heat to the part that isn't' the magnet. it seems to lessen the apoxy

dejitarob (author)2009-04-30

Thanks so much for sharing! I just built one for my mycology projects too and it works great. I only had a few 5 volt power supplies though, so to get 10 volts I wired them up in series like so: + of power supply A goes to - of power supply B + of fan goes to - of A - of fan goes to + of B

jarp87 (author)2008-07-15

very nice im at this step right now. already got the magnets (i broke one of the two aww). one question im no electrician so what if the outpout was 8 v or less then 12? would be ok to use? i have no idea when comes to volt, ohm, amp and all that.

alwinovich (author)jarp872008-07-20

the fan will be a bit slower, my stirrer starts working at 4v(I'm running mine from a variable 0-13v model train transformer)

alwinovich (author)alwinovich2008-08-21

I bought a new vari transformator wich is 0-21 vdc and the fan still works great at 21v i had it running for over an hour non-stop and it didn't fail or get warm

jarp87 (author)alwinovich2008-07-21

let me see if i get it, your "0" its actually 4v? you start from 4-12 v? some mates gave a diagram of how i can make mine to start working at 5v (min) and 12v as max. So you got lots of point to calibrate the stirrer. mine its working and its ok but stirring 1000 ml gets hard. i want to see a tornado in there haha! have pics to share?

alwinovich (author)jarp872008-07-24

yeah, under 4v there is not enough power to let it stir, but it will still use electricity,but yes, it operates 4-12v

Stifling (author)2008-08-10

Great plans, but you gotta pay attention to the magnet polarity. My first attempt at this was a failure because I used a long flat magnet that just happened to have its north and south poles on its faces (like on the top and bottom of a submarine sandwich) and not on its ends. This causes only one pole to ever face the spinner, and it doesn't really move. Once I figured out my problem I replaced the magnet with a smaller magnet that had the proper polarity placement and it worked like a charm.

jarp87 (author)2008-07-15

do you know other magnets source? i wanted to put two magnets in the fan but i broked one..duh

alwinovich (author)jarp872008-07-24

depends on where you live
I think both will ship worldwide, i live in Holland and get mine from

sk8er6 (author)2007-06-21

i like this instructable, although, i only need to mix inks and paints. i like how you can mix one batch at a time, but how do you manage getting the bar out when done? or should i mix in one container and pour into another?

nickdisney (author)sk8er62007-11-26

how about getting a small flat bar magnet to place on the bottom of the container to attract the bar? or some magnet tape along the lip of your container to catch it as you pour?

alwinovich (author)nickdisney2008-07-24

yes, I'm using the same setup, just make sure that the "fan magnet" is strong enough to pull the bar magnet away from the tape

tigergibb (author)sk8er62008-04-07

easy.. just use a magnet on the side of your container. start near the bottom(from the outside) and pull the metal stir rod up the side of the inside of the jar until you get to the top :)

tallest (author)2008-02-15

Rather than buying a lab stirrer you could coat yours in food grade epoxy, the real lab ones are great but not needed unless you're working with really nasty stuff.

Großer Bruder (author)2007-11-13

Do you think you could add a potentiometer to this, allowing more delicate control than on or off? Also, adding something--nonmagnetic but equal in mass and density--to the other side of the interior of the fan would extend its life by equalizing the stress of the magnet.

g0pher (author)Großer Bruder2007-11-13

i honestly dont know since im not very knowledgeable in electronics, perhaps you can try it out and let us know? thanks for the tip on extending the life of the fan!

Cat on my Lap (author)g0pher2007-11-21

It worked out great! I used a relatively strong bit of magnet instead of the hard drive's, but it worked just the same. I used three 5ohm resistors in series as well as a 25ohm, 3watt potentiometer to control the speed. The whole apparatus is covered by a cat bowl to add a buffer region for the magnetic field. It pulls ~3" vortex with 500ml of water on high. The strength can be varied with the resistance, but any stronger and the magnet s won't be able to align.

g0pher (author)Cat on my Lap2007-11-21

great job!

Großer Bruder (author)g0pher2007-11-14

I'll get down to it this weekend and I'll try to get some videos showing the variation on the speed. Also, if one so happens to be a chemist and can't get a hold of the real stir bars for use in caustic and corrosive solutions, if the piece of steel was coated in silicone or HDPE it could withstand some abuse for quite some time. That is, except for use with strong solvents.

cooblades (author)2007-07-20

Someone directed me to you're instructable. It turns out we both built the same thing. I like your pc fan idea, its more readily available. I built mine from Lego. Take a looksie.

Self Stirring Mug

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