Introduction: How to Make a Cheap, Portable Magnetic Stirrer

I needed a magnetic stirrer to keep some cells agitated for cell culture, but didn't want to spend the thirty or so dollars needed to buy one. This magnetic stirrer uses an old computer fan and some cheap neodymium magnets with a moldable plastic stir bar.

The parts are:
- computer fan
- small magnets: (free shipping)
- moldable plastic (polymorph, instamorph, shapelock)
- lexan
-superglue (cyanoacrylate)

Step 1: Glue the Magnets to the Fan

Prepare and clean the fan for use. Your fan may have two wires (red for positive and black for negative). If it has three wires, the white wire is a tachometer and is not needed. Glue the magnets on opposite sides of the fan head. The magnets in the fan's motor may push the magnets around a bit, so arrange accordingly. I arranged the magnets to have opposite polarities facing up.

Step 2: Add Spacers

The magnets will increase the profile of the fan, so you will need spacers before putting a flat surface on top. The spacers can be anything, I used coins initially. Eventually I snapped off a few pieces of spare plexiglass I had lying around and glued them to the edges of the fan. Either way, make sure the spacers are higher than the profile of the fan with the magnets glued on.

Step 3: Add the Main Platform

I cut a small square of plexiglass over the fan as a platform for any containers I will need to stir. Glue or attach any thin, waterproof material to the spacers.

Step 4: Make the Stir Bar

The stir bar is made of two magnets embedded in the moldable plastic. Simply place the plastic in a container of hot water until it turns clear. Place two magnets (polarities opposite facing) onto the plastic and surround with more of the moldable plastic until the magnets are covered. Then round off the edges and mold until the bar is roughly cylindrical with the embedded disk magnets still inside.

Step 5: Powering Your Magnetic Stirrer

The magnetic stirrer can be powered by any voltage source the fan is rated to. However, make sure your magnets are strong enough to couple together from the fan to the stir bar with the rated speed. If the speed is too high, the stir bar will not spin correctly. I used a 9V battery at first, but used this set of 3 AAA batteries I had lying around. I didn't need torrential currents for mine, so I used a lower voltage. This is a magnetic stirrer, not a blender. The lower voltage will result in a slower fan speed, and the stir bar will better be able to better keep up with the fan speed.

Step 6: Use It

Place any container large enough to allow the magnetic stir bar to fit and start agitating/stirring! Since this unit is so small, you can place it on your desk and use it to stir your cold drinks. I wouldn't recommend hot drinks though, heat will cause the polymorph stir bar to soften and lose shape. If you want an improvement, you can try embedding magnets in ceramic and glazing the stir bar.


taratata2015 (author)2017-07-30

with VG not work

Thaikarl (author)2017-05-29

cool. magnetic stirrers aren't expensive:

Austringer (author)2012-10-22

Normally, you don't want to use a stir bar with cells since the action of the stir bar and the bottom of the beaker will lyse them. Roller bottles are the common way this sort of thing is done at bench scale.

UygarO1 (author)Austringer2017-02-08

This could do.

Nyxius (author)Austringer2015-10-22

If there are electrolytes in the water you could induce a flow using emf maybe? I don't know if that would kill them or not though. I've done it in a coffee cup. Really cool, but not terribly easy to apply.

bufalloo (author)Austringer2012-10-22

then that will be my next instructable xD

tnmann10 (author)bufalloo2013-06-05

a cheap multi tier cell roller would be awesome!!!

denewf (author)2015-10-14

I guess old age has finally kicked into the grey matter.

I kinda thought it was the magnets that were the primary factors,

Not air movement!!!

cwright15 (author)denewf2015-11-12

Did you even read it?

denewf (author)cwright152015-11-13

Read it over several times. As I said, it may be my old brain.

Still don't see what air movement has to do with a magnetic stirrer.

Perhaps you might enlighten me?

goobyalus (author)denewf2016-05-09

The fan is just being used as a conveniently shaped, and readily available, motor. The blades aren't important to this.

peapeam (author)2016-02-24

Anybody used something like this to stir e-juice/e-liquid? I never tried making anything like this, but really would like an easy way to stir my e-liquids easily without having to buy a new saw (a lot of people use a saw or tape bottles to their truck wheels and such. Seems like a lot of hassle to me)... If I find a reasonable, used lab stirrer, that may be my best bet... Looked at a vortex stirrer, those do look neat for this purpose, but does cost a bit, especially 220V...

DanielY22 (author)peapeam2016-04-22

i tape small bottles to a drill piece on my cordless and give it a blast. If I am doing 200ml + then i will make it in a lab beaker and put a spoon in my drill and blast it. This would work, but I wouldn't expect the mouldable plastic to last long in the PG.

Vahid777 (author)2016-01-24


Jimmy Proton (author)2012-12-29

If you raise the fain up off the surface it'll run more efficiently by allowing the air to flow through.

ErikC15 (author)Jimmy Proton2015-10-24

I agree it's not so efficient that way, what I did was to cut the blades off the fan. Then the motor can run freely.

IronYeti (author)Jimmy Proton2013-12-10

It turns out this is NOT true. Fans run easiest in a vacuum. If that doesn't make sense, envision the opposite case whereby you try to push heavier air, which would cause the fan to work harder. Having the fan inlet sit flush on the table is perfectly acceptable.

McAldo (author)IronYeti2015-01-25

I am not too sure of that.

Putting the fan close to a surface will not make air less dense.
On the contrary, putting a surface in close proximity to the fan will create a situation in which the fan will have to push the air against a surface, or suck it up from an enclosed space underneath. The latter might create a vacuum to an extent, but I am not convinced that would work the way you suggest, bit like sucking through a straw.
If the fan was to operate in a sealed enclosure with most of the air removed, I agree it would spin faster.

Nyxius (author)McAldo2015-10-22

Sooo of topic, but...

It will run slower until it reaches equilibrium. You two are arguing initial condition versus final condition. Once the area next to the table reaches its equilibrium pressure the fan is no longer doing work and will start to accelerate to its idle speed. (determined by current and phase) Note that the fan will never reach its vacuum speed because it is still losing energy due to heating and stirring the air (really the same thing). If the fan operated in a sealed enclosure then it would behave like the air was part of the rotor. The only losses would be thermal. In a pure vacuum it would probably be possible to spin the fan up till it deformed and started rubbing on the cowling or bearings.

powerfool (author)2012-06-14

I didn't get how you place the magnets. To form one bigger magnet? So, S-N-space-S-N?

0_Nvd_0 (author)powerfool2012-06-15

Let magnets decide. ;)

Yes, S-N-S-N and So oN.

mrmolamola (author)0_Nvd_02015-09-27


FrançoisF (author)2015-06-30

What kind of magnet did you use ?
Because I was wondering if using a neodymium magnet would disturb the mouvement of the fan (which also contains magnets inside).

delor.sander (author)2015-03-06

I have been creating a similar design, but I am looking to take my magnetic fan stirrer into the field. We do experiments in streams, and I am trying to figure out the most effective way to waterproof this design. Any ideas or advice would be appreciated! Right now, the best solution I can see is to seal plexiglass to the top and bottom, but this has proven more difficult than I initially thought...

Huntman00 (author)delor.sander2015-06-28

I would try to cut 6 pieces of plexiglass, one for each side, unless the sides are already sealed. in which case 2 would work. and use Silicone caulking to make it watertight... and you may want to use a lot around there is so there is no seepage.

phil.leahey (author)delor.sander2015-03-09

You could put it in a ziplock bag...

aazzaki (author)2014-05-20

how its works ?

Mark Le bois (author)2014-05-19

Thank you for
these great pictures! I found some more on this website:

AndyPipkin (author)2013-07-18

Can't you just take the fan blade off, and drive the stir-bar from the electromagnets that would have made the fan turn?

tnmann10 (author)2013-06-05


rish113113 (author)2013-04-16

Where will you put the stir bar?? Please reply .

[Bartimaeus] (author)2013-04-13

Awesome build, I was able to make my own with great success. I found a 4 pin fan and a library for Arduino to control the speed with a potentiometer, works well. Want to try again sometime with a fan with LED lighting for effect.

limpport (author)2013-01-11

Are the fan blades necessary to keep attached? It would spin faster without them, unless it makes it spin too fast....

(Then you'll need a resistor or potentiometer!)

7_Volts (author)2012-09-15

didnt understnd yet wht was the use of stir bar and where did u put it ????

EhBmicrobio (author)2012-06-12

Great! Very useful to me.

If you change the batteries by a solar panel, you can enter it into the Green Tech Contest.


well you could get get into the green tech contest anyway becouse it is used with water and rare earth magnets

Krayzi99 (author)2012-06-25

Would you be able to use hot glue for the stir bar instead?

foxworrior (author)Krayzi992012-06-28

i don't see why you cannot use hot glue instead of polymorph, or you could always make one of each.

drdan152 (author)2012-06-22

Great idea !!!! Very cultured haha ..... I'm totally gonna make one of these

foxworrior (author)drdan1522012-06-28

i don't see why you cannot use hot glue instead of polymorph, or you could always make one of each.

foxworrior (author)foxworrior2012-06-28

lol i replied to the wrong person, i meant to reply to pblanscet.

foxworrior (author)2012-06-28

Hello, i have made this but i have made an "improvement", i connected the ground and the positive wires of the fan to a 3.5" mono socket and the positive and ground of a USB cable to the 3.5" mono plugs, and i did the same with a 9v battery clip so i can use either a 9v battery or power from a usb port if i am near a computer.

That is just something to think about if you want to remake it.

ultrabob (author)2012-06-18

Looks like a great idea for yeast starters for homebrewing! Nice instructable!

bulwynkl (author)2012-06-16

the stirrer does not have to be a magnet ofcourse - just magnetic - a piece of steel ( magnetic stainless?) would do the trick. Magnetic would couple better but it's not absolutely needed.

alternatively you can buy Heamatite bars that have been magnetised - these would make an excellent stirrer - Ceramic clean, hard, food safe

random google search shows for example...

(WRT stainless - someone is bound to point out that stainless steel is not magnetic - well that depends on how much Cr versus Ni is in it. Ferrite (body centered cubic crystal structure) is magnetic. Austenite (face centered cubic) is not magnetic. In stainless steels, Ni is a ferrite promoter and Cr is a austenite promoter. High Ni stainless steels are ferritic - this is what stainless steel knives and razors are made of)

bulwynkl (author)bulwynkl2012-06-16

Oops - I got that the wrong way around - Cr is the ferrite promoter, Ni is the Austenite promoter - ferritic CRES has very low Ni.

absolutekold (author)2012-06-15

The only issue i have with ceramics is that some to be properly fired get into the heat range that would effect the strength of the magnets in the stirrer. So i would more be shopping for something that is a food safe polymer resin for general use.. If you're using this for crazy science then be sure it will stand up to what you're doing or consider forming glass. As another aside hacking the fan blades off would help as you are totally restricting air flow and any extra drag is power not going to stirring.. all in all a near concept.

kirkb150 (author)2012-06-15

Make sure that thermo-plastic is food grade if you plan to use it where consumables are involved. (like for home brew "yeast" starter). Just sayin'.

imuhachev (author)2012-06-15

Video, please!)

Spokehedz (author)2012-06-14

Very nice! Couple of cheap (or free) additions would make this even better:

A PWM circuit so that you could control the rate of stir. These are cheap online at various auction sites that rhyme with fleabay.

Removal of the blades so that the rate of spin would be increased dramatically and also give more control when the PWM is installed.

Otherwise, great job!

0_Nvd_0 (author)Spokehedz2012-06-15

If the fan sits on a table, air flow is stopped and the fan speeds up considerably. Will not gain that much by breaking the wings.

If the fan is not that much big, a potentiometer will do a fine job of a speed controller.

About This Instructable




Bio: My name is Alex Ngai. I am currently an electrical engineering student at Cornell University. I’m interested in bio-mimetic walking, running, swimming, and flying ... More »
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