Simple and Small Magnetic Stirrer

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About: Hi! My name is Ignacio, I am an Industrial Design student, who loves creating different things, and playing around with tools and his hands. Also, I am a homebrewer and a music enthusiast.

First of all, english isn't my mother languaje, so you may find some grammatical mistakes in the explanations. I will be grateful if you help me to correct my Instructable. That being said, let's start.

A magnetic stirrer is a laboratory equipment, used for, well, stirring, to enhance or promote some chemical reactions. It's used for stirring low viscosity liquids, using a magnetic bar immersed in the liquid. This kind of stirring has lots of benefits, like being able to stir in a closed container, the use of less mechanical parts than other kind of stirrers (or shakers), being quieter than mechanical stirrers, etc.

A magnetic stirrer is a very useful tool for me: I am a home brewer, and I love growing and culturing my own yeast, first because it's funny, and then, because it helps me to save lots of money, as I don't have to buy yeast. In this article, we can see the benefits of constantly stirring our growth media for yeast, in comparison with the hand shaking of the media, the method which I've been using until today.

But buying a magnetic stirrer is a nonsense for me: they are very expensive, and have a lots of features that surpass my needs, so I decided to build mine, a very simple magnetic stirrer, which will be enough to ensure the best yeast culturing.

Materials Needed

- Cooler, fan (It will be the motor of our stirrer. Mine is a 5v fan from a laptop base)

- Power supply for our fan (I used a 5v charger for an old phone)

- Two small neodymium magnets

- Balsa wood - High Impact Polystyrene (HIPS)

- Some cables and solder

- Male and female power supply jacks

- Glue. I used wood glue, superglue and epoxy bi-component adhesive.

- Plywood

Step 1: Preparing Your Fan and Power Supply

First of all, we got to prepare our motor to be connected to the power supply. So, we have to solder a female power supply jack to our fan, and the male power supply jack to the phone charger. For this project, the polarity isn't that significant, so you can't solder wrong your cables, as you just have two options and both are correct.

In a fan is important a correct polarity on the connections to ensure a proper airflow, but here, we are interested just in spinning, and not in blowing air.

Step 2: Fan and Magnets.

In this step, we are going to make this piece. It will hold the magnets and attach them to the fan. The wood piece is a balsa stick, and both magnets are glued to it with super glue. In this step, there are some variables to take them at count:

-Orientation of the magnets: This magnets have their poles, each one in every face. So we got to glue them one with the north magnetic pole looking upwards, and the other, with the south magnetic pole looking upwards.

-Distance between the magnets: You have to make sure the separation between your magnets is a bit longer than the length of your stir bar

-The piece needs to be glued aligned to the fan axis.

At this this step, I suggest you test your fan, if it still working despite the magnetic influence of your magnets, if the spinning is balanced or not, and if the piece with the magnets interacts fine with our stirring bar

Step 3: The Case

Now, the magnetic mechanism works fine, you need an enclosure to put your fan in. You could use any box big enough to contain or fan, the cable and the magnets spinning, but I preferred to make my box from scratch, to make it as small as possible.

First we need four strips of balsa wood. They need to be longer than our fan sides, and wider than our fan plus magnet plus the piece of wood that holds them. They will be the sides of our prism.

We need to make a hole in one of them, to put the power supply female connector through it. I have made the hole with my drill, and then I modified it with a chisel, as the shape of the connector is like the union of a square and a circle. I made the hole as fit as possible, this will help to keep the jack in place.

To assemble the sides of the box, I've held together the four pieces of wood with tape, while I put wood glue on them. Then I've arrayed the pieces in a squared based prism, and secured them with a rubber band.

After some curing time, I've glued my wood prism to its base, a piece of high impact polystyrene. At this step, I've used some epoxy bi-component adhesive.

Step 4: Assembling

In order to glue the fan in its place, first we need to make some separator to put between the fan and the HIPS, to leave room beneath the cooler for the cable. I've made them with more wood, glued with super glue. Also used superglue to attach the fan in the case, and the connector in the sides of the box.

Now you should check if your magnets aren't beneath the level of the sides of your case.

Step 5: Improvising

The magnets were well located, they weren't higher than they should be. But, when the magnets interacts with our stir bar, the spinning part of the fan raises up, elevating the magnets position, and therefore, putting them in contact with the superior part of the case.

I hope the raise of the fan is noticeable in the video above.

To fix this, I've made a simple plywood separator wich elevates the place of the top of the case, or the stand for the jars.

Then I've tested the stirrer to check if the separator accomplish its purpose.

As you can see in the videos, this build is near its end

Step 6: Finishing Touches

After gluing the separator, I've started sanding the sides of the box. First with sandpaper grit 80, then 150, and 600 for a smooth finishing. I've used some liquid wax as finishing of the wood sides.

Also, I've built a removable plate to put between the flash or the jar, and the separator, to prevent spills to go directly to the plywood.

And that is my first stirred starter, before inoculating on it a wild mixed culture I've harvested from some fruit. You may notice that the color of the starter media was modified in an editing software for the cover of this instructable.

Step 7: Possible Variations.

You can tweak this project at your desire. I made the most simple version of a DIY stirrer, as it satisfies my need. But you could try using a 25 ohm potenciometer to regulate the fan spinning velocity. Also you could use a bigger fan or a dc motor instead of a fan, put an on/off switch, an on/off led, or even use a heated plate to keep your liquid warm. You could use a box you already have laying around in your home/workshop, instead of building one.

Hope you enjoyed my first instructable, and my first tutorial written on English. Any suggestion you have about the project or the instructable, will be well received.

Step 8: Update - About the Magnetic Bar (Stirring Bar)

Some members of the community asked in the comments section about the stirrer, or how to make one, if mine is bought or DIY.

I have two magnetic bars at the moment. They are the ones showed in the photos above. They were bought on Aliexpress some time ago. I decided to bought mine for just one reason: The bough ones are made of PTFE. Let me explain. PTFE (polytetrafluoroethylene), better known as Teflon, is a polymer with very cool characteristics for lab appliances. It is very resistant to chemical corrosion, which allows you to stir lot of liquids with it, without fearing to your bar to be destroyed with the liquid you are stirring. Lets imagine a stir bar made of Polystyrene mixing some nail polish remover, it will be destroyed in a few seconds. That wont occur to a PTFE bar. So, if you have to sanitize it, which is something you always have to do in yeast propagation, sanitize your equipment, you can do it with any chemical, and your magnetic bar will be fine with it. But there are other things about this material. This polymer is a thermostable polymer, which means it can't be melted again after being molded for the first time. This allows everything you built in this material to withstand high temperatures without receiving any deformation, so you could hot sterilize it by putting it on your media while you boil it, which is the method used to kill any microorganism in the grow media used for yeast starters. Also, PTFE has a very low friction coefficient. That is an advantage, because the stir bar has less resistance to its spinning that if it were made of any other material.

But there exists other shapes of magnetic stirrer "bars". I made a model on blender to show you different shapes, without using any internet photo. You may notice that every kind of stirrer has a pivot point, where the bar makes contact with the vessel in which is contained with the liquid to stir. This pivot point is always located beneath the gravity center of the stir bar. These shapes of bars has different uses, related to the kind of stirring you need to get.

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    35 Discussions

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    tcs79

    5 weeks ago

    Hi, Ignadiseñando. I make one magnetic stirrer a few years ago, but had some issues and put it aside until I get time to find what was the exact problem. I think the main issue was the fact that the magnets was not perfectly centered and the fan was spining too fast. (the bar was always scaping to the sides.)
    I will use some of your ideas to correct my prototype.
    Thanks a lot for your instructable. (Your english is not that terrible man).

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    Galt

    6 weeks ago on Step 8

    Great first Instructable, just a few words on Teflon and PTFE's. The short of it is that PTFE's will likely be shown to be one of the greatest polluting compounds on the planet, even worse than the pesticides that now span the globe and infiltrate all of our food. Read it and weep: https://theintercept.com/2015/08/11/dupont-chemistry-deception/?fbclid=IwAR3nuWLnf4P7CueUjIOUfKHQ406DSQr2AZK9yDc4m8SGu7Jg7rpXLKIgjMg They've also come out with a replacement compound called Gen X that's looking like it will prove just as dangerous and destructive, but ya know, there are profits projections to hit, so it's all good, unless you're in the Netherlands or around Cape Fear, where they're making this new garbage. Meanwhile DuPont gets absorbed and redistributed in order to isolate all of its environmental lawsuit potential into one shell that carries few assets, assuring that the resultant lawsuits end at a dry well. Just watch the Monsanto/Bayer maeuvers for a parallel preview of the next step. Not meaning to go political, but this junk is not the benign material that we've been cooking on and told it was for half a century.

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    IgnadiseñandoGalt

    Reply 6 weeks ago

    I knew about Teflon and C8, but until the moment, I though C8 was only used to help applying PTFE as thin coats, as it happens in cocking pans, but I didn't knew it was also involved in compression or transference process, wich are the methods used for producing solid pieces like the stirring bar. Thank you for the comment and the warning.

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    GaltIgnadiseñando

    Reply 6 weeks ago

    For those not inclined to read, here's a documentary that was made on the subject. The story of how the victims in Huntington, West Virginia chose to dedicate their settlement monies to helping expose the even broader impact of this travesty is a story worthy of national hero status IMO. Just ordinary folk, intentionally victimized by DuPont purely to squeeze just one more day's profits from their poisoning, and these people did something extraordinary. But yeah, stay away from anything having to do with those compounds, or their latest convoluted replacements. They are unfortunately ubiquitous in our modern world, but we all need to start walking that back regardless.
    https://www.youtube.com/watch?v=84glf6F3b-Y&fbclid=IwAR2sA6AJXbspZUpr4o8DxRmUosDlcgghaQhM1S-fVN9Ecw1gAiwWadIHkak

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    ZukeMan1

    6 weeks ago on Introduction

    I love it! I’ve seen stirrers on Amazon because I was researching for an answer to my vape juice problem. Their not terribly expensive but when your not full of cash, it’s hard to justify. I wanted to compliment you on what a fantastic job you have done with this ible! I would be happy to help you with your English. Keep up the good work.

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    IgnadiseñandoZukeMan1

    Reply 6 weeks ago

    Thanks, Zuke. I would really like to see you build your own stirrer

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    Alaskan Bev

    6 weeks ago

    I can't envision myself ever needing this kind of simple machine but I loved reading your excellent directions. Even as a retired English teacher, I find that I always have to proof my work for typos. Because you asked, and Only because you asked, the couple of words I noticed were wich, which needs an extra h (as opposed to a witch, a character usually portrayed as ugly and up to no good), as well as bough, which needs a t at the end. Aside from that, I never draw any attention to peoples' spelling. Much better to rejoice over the effort and accomplishment! You have done a fine job and your photos are very good! I could never do as good a job if I had to write in your first language!

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    IgnadiseñandoAlaskan Bev

    Reply 6 weeks ago

    Thank you! Your suggestions were very useful to me, as which is a word I use lots of times. Also, I'm really glad you liked my directions, I think the most important thing isn't the things we say, but the way we say them

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    prampec

    6 weeks ago

    I always wanted to build a tool like this, but as I did not felt the need too much it is always delayed. Nevertheless, I wonder whether the changing magnetic field created by the coils (of a slightly bigger brushless motor) isn't enough to spin the magnetic bar? Just to eliminate any moving parts. (It might just not worth to bother with coils like that tho, when a salvaged fan can do the job.)

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    Ignadiseñandoprampec

    Reply 6 weeks ago

    In fact, I think that 'professional' magnetic stirrers are made with coils, working in a pretty similar way to how a dc motors do, but I dont think that the magnetic field created by these small motor would be enough to move the stir bar.

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    NoelA11mekennedy1313

    Best Answer 6 weeks ago

    If you add a PWM unit into the pwoer supply you will have full control of speed, they can be brought cheap as on ebay

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    mekennedy1313NoelA11

    Reply 6 weeks ago

    That is also true and a good idea, just need a 4 pin fan which are pretty common.

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    Ignadiseñandomekennedy1313

    Answer 6 weeks ago

    No, this stirrer isn't intended to have a stirring speed control, but you could add a 25 ohm class B (linear) potentiometer to be used as a speed control. If you plan to do that, I could make some diagrams for the wiring.

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    tim99

    6 weeks ago

    Nice Instructable. I have one suggestion that will greatly increase you magnetic efficiency. Instead of using a wooden part to mount the magnets onto, instead use a piece of magnetic steel, and flip one magnet to point south pole up, and the other to point south pole down. This will propagate the magnetic field lines into a much larger area, and give you a lot more torque acting on your stir bar.

    You can also mount a single magnet, use a square one for this, on edge to the fan's surface, so that the poles are facing sideways. Then you can then place two pieces of steel against each magnet pole, and bring them up through, or just underneath the underside of your enclosure. Bend them outwards in the shape of a "T" and this will concentrate the magnetic field lines at the best location for moving your stir bar.

    With a setup like that, you could even add a heating element that has an inside diameter that is larger than your "T" structure. Your magnet will be protected from the heat of you make the vertical part of the magnetic pole pieces long enough, and have them just poking through alternating layers of reflective insulation. There's an infinite number of ways this could be done, and you would have an electric heated hotplate stirrer.

    Just remember that when you add steel, or iron, like this, that it extends the poles' field lines of the magnet(s), and it forces them to find the best and closest gap to transverse. This allows you to concentrate the magnetic field lines remotely from the temperature sensitive NdFeB magnet. Look up magnetic circuits and you will see what I mean.

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    ardu11

    6 weeks ago

    Very good, good explanation. 5 stars. Thank you.

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    imerrymary

    6 weeks ago

    I'm learning electroplating but I have a problem because the mixture needs to be stirred occasionally which is difficult with objects suspended in the beaker. This might be the answer if the stirring bar is sealed in something so that no foreign metal is introduced to the plating solution. I hope you post more details about what you used and where to buy it. Well done!!!

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    Ignadiseñandoimerrymary

    Reply 6 weeks ago

    Hi merry! Electroplating is something so cool, great that you are using that technic. About the stirring bar, all labs use bough ones, that are covered with PTFE (teflon). That material is nearly inert, and non conductive, so it wont react with your electrodes or your electrolitic solution. The only thing i dont know about using it on electroplating is if the magnetic field created with this method could interact with your electrical flow in the solution or not.

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    imerrymaryIgnadiseñando

    Reply 6 weeks ago

    Thank you for bringing up the magnetic field and I'll keep that in mind. For now I'm practicing with copper plating over brass charms, then I'll try sterling over brass and copper. There's not much risk in testing on these little charms, so I'm all in! I'll check Amazon for a stirring bar. This 'ible is perfect for my next step. Thanks - and your English is awesome!