Magnetic Stirrer





Introduction: 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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    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.

    Surely you'd want 12V DC adapters no AC

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

    you can also use a 24 volt adapter

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

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

    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


    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 ?

    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!