Homemade stirplate question

I'm having problems with my new, homemade stirplate. I followed the directions from an article in BYO mag, but still can't get it to work right. Whenever I turn it on, it winds up throwing the stir bar.

Last night, when I first started using it, I had a nice vortex going for about 5 min., so I left it alone. When I checked up on it later, the stir bar was thrown to the side of the flask.

I moved the stir bar back into position, and got it started back up again. I watched again for about 5 min, as it built up a nice vortex once again, and left it. This morning, the bar was once again at the side of the flask.

I have the fan on a speed control, but no matter what I do, I can't get the plate to workright !

Does anyone have any ideas to help ?

I would try balancing the magnet on the fan more precisely. If you look at the link in my signature for my build, I use a steel washer to get the magnet perfectly centered. I would also suggest trying a stronger magnet setup. This might aid in keeping the stirbar from throwing. Read through my thread, I have helped a lot of people get theirs figured out.

Your vortex should be pretty slight. you don't need a big tornado down to the bottom of the flask. your vortex is probably hitting the stir bar and knocking it off. All ou need is a slight dimple in the surface for a stir plate to do what it needs to do. It just needs to keep the yeast in suspension and drive off CO2.

The magnet on the fan is as centered as I can get it. What is really perplexing me now is that it looks like the stir bar is just spinning (as in rolling over) instead of rotating with the fan.

kjung said:

The magnet on the fan is as centered as I can get it. What is really perplexing me now is that it looks like the stir bar is just spinning (as in rolling over) instead of rotating with the fan.

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Ah ha! So the magnet is spinning (sort of) on its axis instead of rotating? Sounds like the drive magnet polarity is on the same axis as the fan rotation instead of on the same plane. So the N-S poles are vertical instead of horizontal.