How to make a magnetic stirrer for liquid culture

DIY Magnetic Mixer for home mycology

A magnetic stirrer aka magnetic mixer is often used in labs for buffer solutions that require constant stirring for long periods of time and of course in mycology: for preparation media for liquid culture, agar media and for stirring liquid mycelium.

Laboratory magnetic stirrers can be expensive. If you are using it rarely for home mycology it can be cost-effective to build your own mixer from scratch. Believe me, it's super easy!

The short video below describing the components needed and the steps to build it. Check it out!

Looks easy, isn't it? Now let's check the list of necessary materials and I'll add important notes to each step of the video.

List of materials and supplies needed for magnetic stirrer

I'd like to share components I've used in the video from Amazon. Maybe most of these materials you've already have at home and DIY magnetic stirrer can save your money!

1️⃣ Laptop or PC fan/cooler, size 80-120 mm. In the video I used 90 mm. You can use coolers from 80 to 120 mm

Silent Computer Cooling Fan - 80 mm - 1 Pack $4.89

Ultra Quiet Blue LED Fan Cooling - 92 mm - 1 Pack $5.99

12V DC Computer PC Fan, 2000 RPM - 80/90/120 mm - 2 Pack $12.99

💡 This fan also can be used for incubator and automatic incubation chamber during colonization period. Also for additional fresh air exchange in GrowBox and MonoTub during fruiting period.

2️⃣ Powerful neodymium rectangular magnet block, 20-25 mm is optimal for such version, smaller magnets can be weak for your device

Strong Neodymium Magnets Bars, 25 x 5 x 3mm, 30 pcs $11.99

Powerful Block Magnets 20x10x4mm, Hole 4mm, 6 pcs $8.99

3️⃣ PTFE bar magnet

PTFE Magnetic Stirrer Mixer Stir Bars, 7 Sizes, 7 pcs $8.80

PTFE Magnetic Stirrer Mixer Stir Bar Set, 2 sizes, 8 pcs $9.99

4️⃣ Platform for stirrer. Small square of plastic, plexiglass or even strong cardboard as a platform over the fan for jars or lab cups I will need to stir

Clear Acrylic Plexiglass Sheets, 5 x 7" for 80-120 mm fan, 5 pcs $5.99

5️⃣ A way to power the fan: AC/DC adapter or AA Battery Holder. I suggest to use AC/DC adapter (you'll see why a bit later)

AC/DC Adapter 3-12V, Speed Controller, US Plug for Electric Fan $12.29

8 x AA Thicken Battery Holder Base Box with ON/Off Switch - 2 Sets $6.99

6️⃣ Strong fast glue or Hot Glue Gun for crafting to stick the magnet. I have BOSCH hot glue gun, it's extremely great quality for long-term use, but costly. There are many good cheap alternatives. They are all +/- the same quality

Mini Hi-Temp Hot Glue Combo Pack with 10 Sticks $4.99

Hot Mini Glue Gun with Case and 20 Sticks $13.99

Gorilla Dual Temp Mini Hot Glue Gun Kit with 30 Sticks $14.99

Xyron Full Size Multi-Stick Glue Gun with 10 sticks $15.69

How a magnetic stirrer works

The main principle of magnetic stirrer is interaction between two magnets. The rotating field created by a rotating magnet placed beneath the vessel with the liquid.

The magnet bar in the stirrer are attracted to the one on the fan, and so when the fan spins, the magnet bar spins in the solution, with no physical contact required.

How to assemble magnetic stirrer

Here I'd like to add more important details to my video guide.

Step 1

Prepare all needed components are listed above: computer fan/cooler, neodymium magnet block, PTFE bar magnet, plastic stand, power adapter, glue gun or fast glue, jar with water for testing.

Step 2

I've cut two edges on my fan, because they interfered with the plastic platform installing. It's just a specific of my cooler. In your case this may not be necessary!

Step 3

Glue the magnet block to the PC fan. One of the trickiest tasks is mounting the magnets correctly. That's why don't hurry up!

Magnet should have its poles looking sideways. I've found these sides experimentally (bigger side on the top) and made black mark between poles. So that, right and left sides of the magnet create magnetic field.

❗️Important note: If you use round neodymium disc magnets (8-10 mm) you need to use two magnets. One magnet should have its north facing upwards and the other its south facing upwards. The magnets should be positioned directly across from each other

Step 4

Add the platform. I printed it on 3D printer. If a 3D printer isn’t available you can use any flat surface for such podium: plastic plate, strong cardboard or plexiglass square.

❗️Important note: spacers are needed to sit between the fan and the top platform due to the extra height (3 mm) created by the magnet(s). Coins can be used here or additional small pieces of plexiglass on the corners of the fan

Step 5

Powering your magnetic stirrer. The magnetic stirrer can be powered by any voltage source the fan is rated to. You can use AA Battery Holder or better AC/DC Adapter. Your fan should have two wires (red for positive and black for negative). If it has three wires, just skip the third one.

❗️There is no option of speed control if you use battery holder. With AC/DC adapter your magnetic stirrer will be more reliable, convenient and speed control here is available. That's why I recommend to use AC/DC adapter for your magnetic stirrer

Put PTFE Magnetic Stir Bar in the jar with water, switch it on and test.

Ready!

Ready to use magnetic stirrer

If you don't want to spend time for assembling or you need to order ALL components for such device you can check ready to use magnetic stirrers on Amazon:

Magnetic Mixer 2500 RPM Speed Stirrer with 4 Stir Bars $24.99

Lab Mini Stir Plate Mixer, 3000 ml $26.99

Stainless Steel Magnetic Mixer with stir bar $29.99

INTLLAB Magnetic Stirrer with 7 pcs. stir bar Set and stir bar Retriever $39.99

ANZESER Magnetic Stirrer Hot Plate, 100-2000rpm Lab Stirrers $59.95

Digital Professional Scientific Magnetic Hot Plate Stirrer for Lab $239.99

Enjoy your home mycology and have a happy growing!

This guide made with love by @mrzimm - Tech Guru of Shroomok Growers Community on Discord