My shamelessly cheap $12 DIY stir plate

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Still using mine 2 years later. I need to switch out my box I have it in at some point, but it us not a priority and so far my stirplate has had no issues other than the glue coming undone at one point.
 
My 2L erlenmeyer flask (Karter brand) came in the mail today. My stir plate had no problem powering it with a 1" stir bar.

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I used an old turntable cartridge box I had laying around and mounted the knob to the side, looks pretty slick. Works perfect.

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I see that most of you are putting boxes around yours. I put my flask right on top of the original grate with no supporting box and haven't had an issue. It looks like it would vibrate off but I've left it on for days, and not in some quiet corner either. It runs pretty quiet for a fan.
 
Has anyone successfully fired up a 1 gallon wine jug with this setup?

I once spun a 1" stir bar in a 5-gallon carboy to de-gas mead. The bottom glass was about 1/4" thick.

If it doesn't work, try adding magnets or reducing the space between the magnets and the jug. The magnetic field falls off rapidly with distance.
 
I bought 1 of these fans. Worked out $25AUD with shipping and a crap exchange rate, but still cheap.

If built a 12V one I'd need to do more assembling than this option. The USB fans without a potentiometer are $12 anyway, but don't have the extendable lead.

I just need to find the perfect box to put it in. Every man's eternal quest.
 
My Stir Plate Build - Thanks to all who contributed to this thread. (Took less than 30 minutes to build, added some notes to aid others.)

Used the Following:
- Thermaltake Mobile Fan II External USB Cooling Fan - Us Sold by: Amazon $11.37
- Ceramic Disc Magnet, 0.472" Diameter, 0.197" Thick (Pack of 10) Sold by: Amazon $2.59
- Tupperware container - Raided the wife's cupboard, the stack-able kind with the red lid.
- Gorilla Glue quick set double bond epoxy.

Procedure:
- Dissembled the fan by removing the bolts and nuts.

- Removed the back fan guard and the vertical foot support, discarded.
(The back fan guard could have stayed on but I wanted to use the existing bolts and nuts to mount the fan to the container and was afraid they would not be long enough.)

- Cut the center out of the front guard with a wire cutter. Leaving only the two outer rings on the guard.

- Removed the sticker from the front of the fan and epoxied a 1.5" stove washer to it. (1.5" is the size of the face of the fan blade area making a 1.5" washer very easy to center.)

- Marked the magnets to ensure the North and South sides were able to be placed up. Aligned them horizontally (Eyeballed them) and as far apart as practical on the washer. Then marked the washer by tracing around the magnets with a sharpie to ensure location. Epoxied them to the washer.
NOTE:
Be sure that your magnets are set to as near as practical to the tips of your stir bar. In this case the magnet centers are almost exactly 1" after mounting to the edge of the washer and that happens to be the size of the 25mm / 1" stir bar. If your magnets are too close to the center of the stir bar or too far from the ends of it could throw it while running.

- Drilled a 2" hole in the exact center of the bottom of the Tupperware container using a drill and hole saw. Cleaned up the edges of the hole with a razor knife.

- Positioned the front guard on the plastic container bottom (Now Top) to use as a guide and marked the holes for the fan support bolts to mount the fan. Then drilled the holes using a 3/16 Drill Bit.

- Drilled a 1/2" hole on the "Front" for the speed control and a 1/4" hole for the power chord on the "Back". (Could have went a bit smaller on both but these holes worked fine.)

- Mounted the fan using the existing bolts and nuts. Bolt are placed on the plastic container bottom (Now top) and set pretty flush. (No need to counter sink.)

- Epoxied the speed control to the inside of the container with the knob through the 1/2" hole.

- Epoxied the two prong power connector in the 1/4" hole. It fit snug and took the epoxy well. BE REALLY CAREFUL YOU DO NOT GET EPOXY ON THE PLUG. (I have heard that It's a bugger to get off. Just sayin.)

- Hooked up the connectors and tested. (WOO-HOO!)

- Placed the lid (Now the bottom) on the container.

NOTE - The ridge on the bottom of the Tupperware container (Now the top of the stir plate) is exactly the same height as the modified guard. This adds additional surface area and support for the 2000 mL flask making it VERY Stable.

Pulls a vortex almost to the stir bar on the slowest setting. Ran stable at 3/4 speed any higher pulls too much air and kicks the stir bar. As yeasties get happy and viscosity changes will have more than enough room to speed it up.

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I recently dumped a ton of old hard drives before deciding to build a stir plate. Sigh... I found a package of craft ceramic magnets my letterboxing supplies. They are 3/4" round and have a strength of 6 our of 10 (according to the package). Will two of these be enough to stir a starter in a 2L flask?

Also, what is the best stir bar size and shape? 1" or 1.5" or 2"? Octahedral? Pivot ring or not? Thanks!
 
Need some help please! I got everything built, but it doesn't work. I'm using the Thermaltake fan in thin plastic box from the thrift store. I glued a 1.5" washer on the fan and magnets from Harbor Freight. I have verified that the magnets are positioned so that one is "up" and the other is "down." I have 1" stir bars. The fan spins and everything, but the stir bar doesn't. There seemed to be quite a bit of attraction between the magnets and the fan guard, so I clipped out another ring. Still doesn't work. Any troubleshooting advise would be greatly appreciated. Thank you!

PICTURE
 
What is the distance between the centers of those two magnets.
I'm betting they are way too far apart for a 1" bar.

And the whole spacing thing is why I just went with the bar magnets...

Cheers!
 
What is the distance between the centers of those two magnets.
I'm betting they are way too far apart for a 1" bar.

And the whole spacing thing is why I just went with the bar magnets...

Cheers!
Not sure, but when it didn't work, I tried moving them out to the edge of the washer as well as toward the center of the washer. So far, it still didn't work in any of those three spots. :(

I had 24 old hard drives that I dumped a few months ago before I decided to build this. I went with the rare earth ones from Harbor Freight since they were recommended by somebody else in the forum (plus they were inexpensive and quick to get), but I'm not sure if they aren't strong enough or there is some magical spacing that I haven't yet discovered...
 
Need some help please! I got everything built, but it doesn't work.

I used a flat washer and four rare-earth disc magnets. Super glue holds the whole thing together. The magnets are 1 1/8" center-to-center, and it spins a 1.5" stir bar.

Tune the height of the magnets so they barely clear the flask. Millimeters count. I used some bolts and nuts that allow an adjustable height.

[Edit: This is an 80mm case fan and custom LMC555 PWM controller built from spare parts. Not the same innards as the OP's USB fan, but the magnetic path to the stir bar is the same.]

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Need some help please! I got everything built, but it doesn't work. I'm using the Thermaltake fan in thin plastic box from the thrift store. I glued a 1.5" washer on the fan and magnets from Harbor Freight. I have verified that the magnets are positioned so that one is "up" and the other is "down." I have 1" stir bars. The fan spins and everything, but the stir bar doesn't. There seemed to be quite a bit of attraction between the magnets and the fan guard, so I clipped out another ring. Still doesn't work. Any troubleshooting advise would be greatly appreciated. Thank you!

PICTURE

Not sure, but when it didn't work, I tried moving them out to the edge of the washer as well as toward the center of the washer. So far, it still didn't work in any of those three spots. :(

I had 24 old hard drives that I dumped a few months ago before I decided to build this. I went with the rare earth ones from Harbor Freight since they were recommended by somebody else in the forum (plus they were inexpensive and quick to get), but I'm not sure if they aren't strong enough or there is some magical spacing that I haven't yet discovered...

Probably not strong enough, that was the problem I was having when I couldn't get it to spin.

I used a flat washer and four rare-earth disc magnets. Super glue holds the whole thing together. The magnets are 1 1/8" center-to-center, and it spins a 1.5" stir bar.

Tune the height of the magnets so they barely clear the flask. Millimeters count. I used some bolts and nuts that allow an adjustable height.

[Edit: This is an 80mm case fan and custom LMC555 PWM controller built from spare parts. Not the same innards as the OP's USB fan, but the magnetic path to the stir bar is the same.]

Well, I think I've given up and will abandon this project. I had originally set it aside because I was frustrated and recently was able to get some hard drive magnets. I thought that the upgrade would do the trick, but I could only get it to spin the bar in about 4 fl oz of water in an 8 fl oz jam jar about 25% of the time. It absolutely will not work in either of my Bomex Erlenmeyer flasks or anything larger. It also seems that anything with just a slightly domed bottom is totally doomed to fail (including my Erlenmeyer flasks). Note: I have 1" octahedral bar with pivot ring (PICTURE).

Thank you for the suggestions. I appreciate the comments and help, but it just still won't work. At this point, I'm really unsure what to do or try...
 
I could only get it to spin the bar in about 4 fl oz of water in an 8 fl oz jam jar about 25% of the time.).

You are close to success - your project works, sort-of.

As you've discovered, the problem isn't the magnet. I suggest there is still too much air/glass gap between the magnet and the stir bar. One-over-r-squared is one of those fundamental laws of physics that we are not allowed to break.

Suggestions:
1) If you haven't already, use bolts/nuts to support the Erlenmeyer. The bolt/nut support allows minimal spacing between the spinning magnets and the glass. Look at my picture again - you're seeing a felt "dot" on top of a machine screw, supported by nuts. Infinite adjustability - my Erlenmayer barely clears the magnets.

2) Try stacking two (four total) magnets. That doubles the flux. Again, the bolts/nuts allow minimal spacing. If you look at my picture, there are TWO (four total) stacked magnets. Using only one didn't work for me.
 
Using mine. I didn't build an enclosure for it, just cut part of the fan guard off and set the flask on that. Works great!
 
After I built it and tested it, I moved and haven't yet had the chance to use it to actually make a starter. I'm looking forward to it though. I've resolved to brew more this year, so I'm sure it'll get a workout. I enclosed mine in a box that my other fan (for air circulation in my fermentation chamber fridge) came in. It works very well.
 
Yep still using it. Have made well over a dozen Ciders and Meads with it. Do a Yeast Starter in a 2000 ml flask and let it run for 48 = 72 hours. No issues. Notes in previous post describing my build still apply.
 
I found the best way to place magnets is to stick them to the stir bar
so they'll settle where they want to be, then stick them to the washer.
 
Mine is now 7 years old and still functional whenever I need it. I should upgrade the box its in at some point. I guess I will add that to my brewing to do list, I have had the box sitting around for years ready for it.
 
I pulled mine out after a 4 year hiatus. It took many tries to get the stir bar going but once I remembered that you have to start the fan on fast, not slow, it caught. I then used it for my starter and the stir bar caught on the first try every time I restarted it. I still haven't enclosed it in anything, I just place the flask down on the fan grate and it stays even though it looks like it would vibrate or slide off. I have some cork sheeting that I may place over the fan, but only if it would still work with the extra 3/16ths of an inch.
 

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