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make your own magnetic stirrer

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I was going to post this a while back but got stuck into some uni work so here it is...

 

I wanted a magnetic stirrer but I didn't want to pay $100+ for one so I decided to make it from what I had in the garage. The idea was to use an old fan, a couple of magnets, a stirrer bar and a power supply.

 

Here's the list of things that I used, remember that you can use a vast range of alternatives depending on what you're going to use the stirrer for (I need(ed) it for a couple of chem experiments):

 

- 12 V (0.15A) fan from an old power supply

- 6 x neodymium disk magnets (4 x 5mm)

- magnetic stirrer bar (white, coated)

- power supply (5-6V)

- 5 pieces of wood, 6 nails and 2 screws

- plastic cd case

- some sticky tape or other glue

(and you might need ruler and pen if you're not good at cutting things approximately)

 

How to make it (I won't go in depth with description as it should be pretty obvious from the photos at the end):

 

Starting off with the fan, I ripped it out of an old power supply, rated 12V. I was going to use it to carry 6 x neodymium magnets stacked together and centered on top of the fan, fixed by some sticky tape.

 

Neodymium magnets I was going to buy as I wanted them for other things too but then ended up stealing a couple of magnetix pieces from my brother's toys section, you can do either :). Stack them together to form a larger magnet and stick them onto the fan.

 

Power supply I already had but if you don't have one you can also use one of those 6V batteries or add up a 4 of 1.5V ones, up to you.

 

Professional stirrer bars (white plastic coated ones) you can buy for a dollar or cheaper, or alternatively you can use 3-4 neodymium magnets and coat them yourself, or even use whatever else magnetic you've got- I'm sure you can find something around.

 

Finally, you'll need a housing able host all parts of the stirrer; I used a couple of wooden blocks that I already had, which came handy because I was able to screw in 2 screws to fix the fan so it doesn't move. I actually used a saw to cut the top 3 pieces so that they fit, but I really didn't pay much attention to the overall design of the housing at all, as long as it stood firm and simple. I also used one piece of a plastic cd case as the top plate on which I would put the flask/beaker. You can glue in or fix this plate with some sticky tape if you want.

 

Once everything was assembled I gave it a test run, and it worked :) However, I found that it will not work well at over 10-12 V, if you manage to get it to that, at which voltage you'll be observing quite a dangerous twister that knocks the stirrer bar out of sync more often than not. The part where I try to reach the highest rpm was quite addictive actually, gotta love those twisters.

 

As a further note, I realized there are quite a few things that could use improvement. These include the removal of blades on the fan so that it doesn't cool the beaker (unless of course you want it to cool, or heat for that matter by directing the heat from a source onto the base of the beaker, you'd need the heat source though, which wouldn't be very practical due to limitations, maybe 40 degrees C), use of more than 6 magnets for greater stability and higher rpm and use of stronger magnets for stirrer bar amongst other things.

 

Nevertheless, so far it served the purpose and can keep stirring continuously at 5V for as long as you want it. I kept it on a test run for 12 hours without problems.

 

Photos attached.

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Fantastic. :) I have a hotplate+stirrer combination but if I didn't I'd probably build something like that as I have some Nd-magnets and suitable fans. I wonder if you could fit a heating element in between the surface (glass in that case) and the fan and magnets.

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I didn't need the heater so I didn't think about it much.. I might try to implement an electric hotplate as the top holder plate in that design, in which case I'll have to change the housing too; if I ever get around that idea I'll update :)

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Actually nevermind the glass surface, I was just thinking "magnets -> don't use metal" for some reason. :) I'd imagine an aluminum or copper surface would be OK for sufficient thermal conductivity.

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