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.

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

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.

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.

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.

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

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!

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.



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    70 Discussions


    11 years ago on Introduction

    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.

    1 reply

    5 years ago on Introduction

    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


    7 years ago on Introduction

    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 ?

    3 replies

    Reply 7 years ago on Introduction

    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!


    Reply 7 years ago on Introduction

    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


    7 years ago on Step 2

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


    7 years ago on Introduction

    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.


    9 years ago on Step 3

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

    2 replies

    Reply 9 years ago on Introduction

    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 :)


    Reply 8 years ago on Introduction

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


    9 years ago on Introduction

     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!


    9 years ago on Introduction

     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 :(


    9 years ago on Introduction

     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.


    9 years ago on Step 8

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


    11 years ago on Introduction

    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!

    2 replies

    Reply 10 years ago on Introduction

    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.


    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?