DIY Stir Plate Problems

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Hops

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I am trying to make a DIY stir plate but all the "pea" does is jump around. It won't spin. I am using a 12v dc 4 inch computer fan powered by either a 5.9 v or a 9 v wall wort. I have tried 1 magnet, 2 magnets one on top of the other, and 2 magnets on opposite sides of the top of the fan. I have adjusted the distance from the spinning magnets to the "pea" from about 1/4 " to 1 1/2 ". I have read every post about the DIY stir plates and looked at all the pictures. But this *@%#$^ "pea" won't spin. Someone out there must have had the same problem... HELP.
 
How large is your stirbar? My 2" barbell is way harder to get spinning than my 1" one. What kind of magnets are you using? If you use a Hard Drive magnet 1 should do the trick, the round ones will take 2. And use a spacer (PVC/SS Washer/Wood) of some sort between the fan and magnet.
 
I don't know what "pea" stands for, but what kind of stir bar do you have? Mine's about 1.5 inches long, and I have two magnets about a cm in diameter each that are placed just under the outer edges of the stir bar. Mine took a while to get right, but it's pretty much as close to the plexiglass it'll go before the fan tries lift off the table (mines not attached yet). You might let it sit on the magnets for a minute or so and make sure the poles aren't confused. I think this helped mine finally get locked in. Now it works every time w/o fail.
 
Sorry about the technical terminology... "pea" equals stir bar. I am using a 1 inch stir bar. The magnets are from a hard drive. I will try the spacer between fan and magnet. The stir bar is currently sitting in the magnet hopefully that will allow it to orient itself correctly.
 
Hops said:
I am trying to make a DIY stir plate but all the "pea" does is jump around.
Click to expand...

If it doesn't sound like your fan is struggling to spin, it might be a polarity issue... I had a similar problem in that the bar didn't want to center itself on the magnet. I went to Ace (they have very cheap Neodymium magnets BTW) and bought circular magnets.

At first I though I was having the same issue...
IMG-20110401-001061.jpg

But by flipping one of the magnets, the poles lined up and the stir bar found its happy place...
IMG-20110401-001071.jpg

On the actual fan, I epoxied a thin steel washer so I could adjust the magnets if necessary...
IMG-20110401-001091.jpg
 
Is the bar getting thrown to the side immediately? If so you might just be starting it off too fast. I've found it's best to start the motor off barely spinning, let the bar get started, then increase the speed.

If the bar stays centered but doesn't spin, you just need more powerful magnets. HDD magnets didn't work for me either, so I got some rare-earth magnets, and now I can spin the bar in a 3 gal carboy. If you have a Harbor Freight nearby, they'll probably have some in stock.
 
Other thing to consider ... is the center of the magnetic field (not the center of mass) centered on the fan? With a hard drive magnet I don't think the two are the same due to the odd shape. Let the stir bar find it's location on the magnet, the point in the middle of the stir bar needs to be centered on the fan.
 
Thanks guys. I ended up not using the free hard drive magnets and going to ACE for the round ones. Inverting one of the magnets and allowing the stir bar to orient itself was a key factor. Also using the spacer between the fan and the round magnets helped. I now have an almost free stir plate. GO YEAST!! GO BEER!!
 
I have a question about the circle magnet. I bought some rare earth magnets from harbor freight, 10 for $3 and they are about the size of a pencil eraser. I built my stir plate just like everyone else, but when I put the stir bar on top of the stir plate, the fan blade actually pulls up and sticks to the roof of the box and won't spin even on full power(5v wall wort). If I move the fan down just far enough where it doesn't pull the blade to the top of the box, the attraction isn't good enough for the stirbar to be affected at all by the magnets. Do I just have a cheap POS fan? too strong of magnets? Too weak of power supply?
 
Fooch said:
I have a question about the circle magnet. I bought some rare earth magnets from harbor freight, 10 for $3 and they are about the size of a pencil eraser. I built my stir plate just like everyone else, but when I put the stir bar on top of the stir plate, the fan blade actually pulls up and sticks to the roof of the box and won't spin even on full power(5v wall wort). If I move the fan down just far enough where it doesn't pull the blade to the top of the box, the attraction isn't good enough for the stirbar to be affected at all by the magnets. Do I just have a cheap POS fan? too strong of magnets? Too weak of power supply?
Click to expand...

I had this exact problem until I picked up the same magnets at Harbor Freight. I placed small rubber washers between my box lid and the fan body and it worked perfectly. I did buy a nice case fan from Staples and am using a 6v power supply I bought at Radio Shack. Granted I spent about $40 for my parts, but it beat $65+ for the cheapest ones I could find. It did take a bit of work to find the happy medium of space between the magnets and the lid of my box. Also, having a variable speed control helps a lot. I let my stir bar orient itself on the stir plate then slowly increase the speed of the fan until I get a nice little 'tornado' going. I haven't found if that is the sweet speed, but I notice my yeast is happiest at that speed.

Mouse :mug:
 
CA_Mouse said:
I had this exact problem until I picked up the same magnets at Harbor Freight. I placed small rubber washers between my box lid and the fan body and it worked perfectly. I did buy a nice case fan from Staples and am using a 6v power supply I bought at Radio Shack. Granted I spent about $40 for my parts, but it beat $65+ for the cheapest ones I could find. It did take a bit of work to find the happy medium of space between the magnets and the lid of my box. Also, having a variable speed control helps a lot. I let my stir bar orient itself on the stir plate then slowly increase the speed of the fan until I get a nice little 'tornado' going. I haven't found if that is the sweet speed, but I notice my yeast is happiest at that speed.

Mouse :mug:
Click to expand...

I'm sorry I didn't explain it well enough. I have 4 bolts coming down through my top lid of the box(radio shack project box) and I have a nut on each of the bolts tightened right up to the lid, then I have a rubber grommet(like a thick 0-ring) under those, then I have the fan under that, and then 4 nuts under the fan to hold it on. The actual fan casing doesn't move at all. The actual blades that spin within the casing, that whole piece pulls up about a quarter of an inch out of the casing and sticks to the roof of the box. I am at work now I will post up some pictures of it when I get home.
 
The strength of the hard drive magnets alone aren't impacting the motor - but when the stir bar (or anything else attractive) comes near them, they're straining to get to it!
you'll have to find out the maximum distance that fan blade can travel, and adjust those nuts/grommets to a millimeter or two less. Some fans have more 'wobble' built in than others. Of course, getting the magnets off the hub with spacers seems to help so they don't influence the motor quite so much, but they'll still 'pull' toward whatever magnet they can.
 
Fooch said:
I'm sorry I didn't explain it well enough. I have 4 bolts coming down through my top lid of the box(radio shack project box) and I have a nut on each of the bolts tightened right up to the lid, then I have a rubber grommet(like a thick 0-ring) under those, then I have the fan under that, and then 4 nuts under the fan to hold it on. The actual fan casing doesn't move at all. The actual blades that spin within the casing, that whole piece pulls up about a quarter of an inch out of the casing and sticks to the roof of the box. I am at work now I will post up some pictures of it when I get home.
Click to expand...

Actually, your's sounds exactly like mine. I had the same issue with the fan blades lifting up against the bottom of the lid. I added rubber grommets that are about 4mm thick and that solved the issue.

Mouse

:rockin:
 
I just built mine & was having some trouble at first. I bought two 1" stir bars, but only one of them worked - it had a different diameter than the other. It might just be a factor of finding the perfect size stir bar. See if you can borrow a variety of sizes from other people in your local homebrew club.
 
Thanks everyone for the suggestions. I got it working!!! It was a combination of four things:

1.) I loosened the nuts holding the fan on to drop it down JUST slightly
2.) I got a 1.6 inch stir bar(couldn't get a good cyclone and had throwing issues.
3.) I moved the disc magnets out far enough so that they are at the very ends of the stir bar instead of closer to the middle
4.) I got a radio shack adjustible wall wart to up the power.

IMG_20130209_183110.jpg
 

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