Throwing stir bars?

O after much tinkering I finally built my own stir plate with a 120 mm fan and a lm317 and a potentiometer to govern it. I glued a washer to the fan and two 1/2 inch magnets at opposite ends. The only stir bar I can get to spin is only one inch long anything bigger goes off balance at high rpms. What am I doing wrong?

I have the same issue with my stir plate. It spins a 1" bar perfectly. I temporarily lost the 1" and ordered a 1.5" and it would continuously throw it. I saw a suggestion here somewhere that your magnets should be further apart with larger stir bars. Before trying that though I found my 1" magnet. At least in my case the 1" stir bar does a great job; it will easily bring the vortex down to the bottom in 2 liters of water (in a gallon jug).

just a note that i kept having trouble with mine throwing as well when water testing. I got the magnets as close i could to the inside of the box and just decided to go with it anyway. Once i had wort in there, it was way different. 2 days, never threw the bar once. Remember you dont need high rpms. Even a slight dimple on the surface is enough stirring.

I used some bar magnets, essentially making one 2 inch long magnet across the center of the fan, it seems to work better for various sized bars. However the simplest and best solution is don't use the high rpms stirplates are used for yeast starters to get continuous agitation, it doesn't need to be real violent. I successfully used a 1in stirbar in a 5 gallon bucket to make a starter before, one of the best ferments I have ever seen

I am not aiming for high rpms I am just trying to get the bar spinning. It will make a few rotations them bye bye. I will try playing with the mag configuration and see what happens...

I use LM317's as well with a 10K pot. It may not be your stir bar. When I fire mine up I have to quickly turn the pot down to half power or the bar will throw every time. It needs more power to get started, but then I have to quickly turn it down (like immediately upon pushing the on button). I'm not saying that this is definitely your problem, but try it and see if it helps.

That is ironic because I have to quickly turn mine up or the small bar will throw, and vis versa with the bigger bar

HenryVance3 said:

O after much tinkering I finally built my own stir plate with a 120 mm fan and a lm317 and a potentiometer to govern it. I glued a washer to the fan and two 1/2 inch magnets at opposite ends. The only stir bar I can get to spin is only one inch long anything bigger goes off balance at high rpms. What am I doing wrong?

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I fixed a similar problem by adding a small silicone O ring at each end of the stir bar. It still throws it a high RPM, but it works pretty consistently at low to moderate speeds.

I would say just raise your fan/magnets up putting them closer to the bottom of the flask/ stir bar. Mine are very close to the underside of the cover, which puts it less than a 1/4 in away from the Flask.
Snake10

I have built 4 of the plates and each one acts a bit differently. The main thing is gonna be magnet placement. The bar cannot be longer than the diatance between the magnets.. secondly believe it or not is the placement of the flask on the stir plate. I do not believe the flasks are perfectly flat in every case and the bar seems to just ride better at different locations in the bottom of the flask.when you start the plate up, does the bar clang or chatter ? if it does slowly move it and you will hear it get almost silent. Thats the sweet spot.

That makes sense. Thanks man!

Problem is solved, I re set the magnets with the stir bar in the fan itself and ran it adjusting the magnets until the bar was perfectly centered and BAM! I am stirring baby! Thanks everyone for your help.