DIY Magnetic stirrer

[Thexder]

If you are like me who needs to mix additives to maintain Ca, Mg, Ph, Kh in your tank. You will know how difficult it is for some of the additives to dissolve in DI water. Of course you can just dump the additives in your sump but it can do more harm when the additives don't dissolve fast enough and lands on your corals.

I'm lazy to stand or sit around to stir the solution until it mixes completely, so I've decided to DIY a magnetic stirrer. This is used in labs to mix chemicals. Basically it has a magnet on a motor. There is a stirring bar in the container which is magnetised also. When the motor turns, the bar also turns by magnetic force thus mixing the solution in the container. Some of them also have a hot plate to heat the solution, but we don't need that for our purpose. Such units cost around $200 or more.

After checking other DIYs on magnetic stirrers, here are the basic parts you need:

1) Motor - Most people use the fan from a PC

2) Strong magnets - Most people strip the magnets from a dead hard disk

3) Stirring bar - Can buy or make your own from iron/magnet

4) 12VDC supply

[Thexder]

A trip down to Sim Lim Tower and I got the following:

Project box: To contain the fan, electronics, and also to support the container for mixing. This cost me $4.50 but you could get an unused Tupperware box from your home and its FOC. The box must be plastic (or non-metallic). If you use a metal box, the metal will interfere with the magnetic field and you won't get good results.

[Thexder]

12VDC fan for PC. I got this design because it has a good flat and unobstructed surface to attach the magnets. Otherwise the standard PC 3" fan will do. The cost was $8.80 but its FOC if you can get from a spare or dead PC.

[Thexder]

PWM speed control. The fan speed has to be controlled. If it spins too fast, the magnetic force is not strong enough to couple the stir bar to the fan. I opted for the PWM because its a more efficient way to control a DC motor but the cost is higher. This kit cost me $9.60. You can use a cheaper option by using a potentiometer to change the voltage to the fan directly (probably $2-$3).

[Thexder]

Magnets. You need quite a strong magnet to spin the stir bar, and HDD magnets are the easiest to get for the rare earth magnets. I got this pair from the junk shop on the top floor of SLT for $4. Its FOC if you have a dead HDD lying around...

[Thexder]

Some other miscellaneous parts like control knob, power switch, adaptor pug. Other parts not shown here which I have in my spare parts box - LED, wires, resistors, screws, etc.

[Thexder]

Last but not least, 12VDC power supply. Cost is around $12-$15. Again its FOC if you have a spare one lying around as a charger for handphone, phones, etc. Otherwise, your PC power supply is also possible

[Thexder]

First we got to remove the magnet from the steel plate. They are normally glued on. I used a hammer and flat head screwdriver to remove them. If you whack too hard, the magnets might break. Just a few firm taps will do.

[Thexder]

Attach the magnets to the fan. You need to glue or stick them (I used 3M double sided tape) or they will fly off when the fan spins too fast. Also note that you need to find the right position to place them otherwise the rotation is not balanced and the fan will probably wear out very fast. 1 magnet is actually good enough.

[Thexder]

Ok, now to assemble the PWM speed control. Opened the package and damn... the instructions are in Thai

But just follow the circuit diagram which is self explanatory. Again if you are not confident in soldering or electronics, then better to use a simple solution with the potentiometer as the chances for making mistakes are lower. My circuit didn't work the first time because I soldered a diode in the wrong direction

[Thexder]

Mechanical assembly of the enclosure. Some drilling and cutting required to insert my power switch, control knob.

[Thexder]

Fully assembled with the fan above the speed control PCB. I used wall plugs and PC spacers to raise the fan height. You need the magnet to be near the top surface. I added the LED to indicate power on. The switch is supposed to have a light when power on, but didn't seem to work or I don't know how to connect it

As can be seen, I used 1 magnet which is sufficient.

[Thexder]

Side view to show the clearance below.

[Thexder]

The completed DIY magnetic stirrer

[Thexder]

Testing with a small bar magnet as the stirring bar in a 100ml jar...

I'm now trying to DIY a stir bar. You can buy the commercial lab stir bars but I enquired and it costs like $10~$30 for 1

Supposedly, a nail, metal wire or paper clip should work, but doesn't seem so in my case.

Will add more updates once I have a proper DIY stirring bar.

[albinosage]

Phweeeeet~

Nice DIY project, thanks for sharing!

[Gouldian]

Nice... Thanks for sharing!

[maxteo98]

nice idea! seems like it can be further refined to work like a vortech wave maker.

[Thexder]

nice idea! seems like it can be further refined to work like a vortech wave maker.

The same concept is used in kalk stirrers.

[jyoon]

Hi Bro

Thanks for sharing. Will try out.

[peacemaker]

Sweet DIY! 　

[Thexder]

I found this shop called Practical Instruments located at Balestier Hills Shopping Centre which sells the magnetic stirring bars. $5 for a 1.5" stir bar. They have other sizes too. They sell laboratory instruments and consumbles so you can get other lab supplies also.

Anyway, I'm still trying to DIY a custom stir bar or plate for my other container which has an uneven bottom.

[reef999]

Thanks for your great idea!!

Today i hv done a simple one without the speed controller and box.

I am using the 12VDC adjustable voltage adapter for the 12V fan.

Also DIY a stirring bar.

6V setting result.

And video showing adjusted from 0V-->4.5V-->6V-->7.5V-->12V-->0V.

[Thexder]

Great! Can show how you DIY the stirring bar?

[reef999]

I am using the some small broken magnet from hard disk and insert into a teflon block.

Here's the cross section view