5000ML (5L) stir plate build

Finally got around to making a proper stir plate for my 5000ML flask. I could not find any cheap versions for a large flask.I had some issues with using a 2 inch stir bar so I went down to 1 inch and it works fine. The wood is a soft wood that I had hanging around the shop. I hollowed out the back for the computer fan. The wood is 1/4 thick over the magnet. The fan is held off the wood by 1/4 spacers. Rubber feet allow for air circulation. Standard rocker swithc for on and off and a rheostat for speed control.

testing to make sure it works before solder.


final product.
If I had to do it over I would make a removable power cord.

looks great! I love the idea of carving out spaces in the wood...mine's just in a little plastic radioshack project box

Nice work!

snowveil said:

looks great! I love the idea of carving out spaces in the wood...mine's just in a little plastic radioshack project box

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Thanks, that's the benefit of having a CNC router.

I have a question, I guess it may be more general than this specific build, but I think this is a valid place to ask it.

How does the fan cause the stir bar to move? Are there magnets on the fan blades? Or does the stir bar rotate based on the magnetic field created by the rotating motor?

Also, what issues did you have with a 2'' bar?

Devo2k said:

How does the fan cause the stir bar to move? Are there magnets on the fan blades? Or does the stir bar rotate based on the magnetic field created by the rotating motor?

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Magnets are generally mounted to the hub of the fan. There's a pretty great guide located here

As for the 2" stirbar issues...my only guess is that the magnets weren't perfectly mounted and caused too much vibration and continually threw the bar away. I've only ever used a 1" bar on mine so this is definitely pure speculation....

Devo2k said:

I have a question, I guess it may be more general than this specific build, but I think this is a valid place to ask it.

How does the fan cause the stir bar to move? Are there magnets on the fan blades? Or does the stir bar rotate based on the magnetic field created by the rotating motor?

Also, what issues did you have with a 2'' bar?

Click to expand...

I superglued a metal washer to the fan. Then I put an old hard drive magnet on the washer ( it sticks by magnetism or you can superglue that as well). The stirbar is a teflon coated magnet. When the fan is turned on the stir bar turns. I can control the spped with the rheostat. The two inch bar kept getting spun off the magnet. I guess the magnet was not strong enough to hold the 2 inch one.

Very well done!

That is a thing of beauty!

Looks good! Mine is in a cigar box, i like yours better.

I'm looking to duplicate your build. Are you happy with the 1/4 thickness of the wood over the magnet?

On my build, I used rare earth magnets I found at an electronics store, 3 for $2.5, and just spaced them further apart/ to the outside of the washer. I get a little more rattle with the 1" bar but the 2" bar just mows down my 5L flask like it was a little .5L flask!
Home made stir plate mowing down 5Ls like it was nothing! by ZX3Tuning, on Flickr
little higher than 1/2 speed and its a solid and stable full vortex to the bar.
ran like this for 40hours after I first built it without a complaint!


I over built mine and while it might not be a wide enough base to do it, I'm pretty sure it's strong enough to get a good vortex in a 6.5Gal carboy... just have to wait for one to free up!

What are the specs of the fans you all used (mA, rpm, volts)? And the rheostat?

I built a stir plate and bought a wall charger with 6 voltage settings to use as my rpm controller. Problem is that I have to unplug it to switch settings. It's fine with my 1" bar but the low voltage setting isn't strong enough to start my new 2" bar and the next setting starts spinning the fan too fast for the bar to catch up. In either case, I can't get more than a 0.75" deep vortex going.

Plus this fan I use need a little help to get started.. have to spin it a little with my finger. Seems that the magnets within the fan aren't strong enough for a self start when the axis is vertical.

I'm thinking I need a stronger fan that has a higher amperage draw? I'll read other threads on how to size match a rheostat but would appreciate any quick guidance there, too. Thanks