Why does my stir magnet fly to the side of the flask?

I built a stir plate with the magnet of a hard drive like so many. I used a pot and everything I saw in a couple of videos and threads. As soon as I turn on the fan the bar flies to the side of a 2000 ml beaker. Any Ideas why? Thanks.

CourtHouseBrewing said:

I built a stir plate with the magnet of a hard drive like so many. I used a pot and everything I saw in a couple of videos and threads. As soon as I turn on the fan the bar flies to the side of a 2000 ml beaker. Any Ideas why? Thanks.

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There are a few reasons this can happen. Normally it's because the bottom of the container isn't flat which shouldn't be the case with your beaker. You can also try using a smaller stir bar. From my experience, larger bars throw a lot more easily than smaller ones.

Also, the speed should not be going full bore. I'd set it just fast enough so that the yeast is suspended. Certain yeasts will begin to clump after some time, especially with larger starters, so you may need to speed it up if you see this happening.

-TK

magnet and stir rod are deflecting each other?

How well does it work if you eliminate the beaker and just place the stir bar on the plate? My initial guess is that the plate material is too thick or you've got too much space between the HD magnets and the pot (plate surface). In either case, a weak magnetic field acting on the stir bar. Assuming you're not just cranking up the fan full bore of course.

Another problem may be that you don't have the magnets' polarity correct on the fan. If you have both of them oriented the same it will throw the bar every time, I learned this the hard way.

Thirteen said:

My initial guess is that the plate material is too thick or you've got too much space between the HD magnets and the pot (plate surface).

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That was the problem with mine. I adjusted it about 1/16" and now there is no spin off. It doesn't take much.

I have also had the space between the magnets not enough. I have to use two pieces of cardboard on top of the stir plate to make it work well. Getting stir plates to work correctly takes a lot of tinkering.

so I've made a few stir plates now, all with HD magnets, and I can't get them to work well when the I leave the curved HD magnet in one piece. I have to break them in half, which allows me to line them up straighter. I think the curved shape makes it difficult to get the stir bar to line up with the center of the fan.

Here's what I do. Break the magnet in half to make two, equal sized pieces (if the magnets are smaller sized ones, then break two of them and keep the big ends of each break). Use your stir bar to check the polarity of the magnets and line the magnets up under the stir bar so that each end is being pulled down by the respective magnet. Now, you should have two pieces of magnet lined up together and stuck to the stir bar. Then place them all on the center of your fan--the magnets should stick to the fan and, with a little help from spare fingers, you should be able to remove the stirbar and keep the magnets stuck to the fan. Test it out and make adjustments as necessary. When things are right you should be able to start the fan full-bore without throwing the bar. Once you get it right, glue down the magnets with some super glue. I drop super glue around the edges, so I don't have to pick up and move the magnets, which might make me lose the magic spot.

Hopefully, this makes sense--it does take some tinkering. Good luck!

Tagged for future reference -- desperately need to adjust my stir bar plate as I'm constantly have to fool with it to get it work properly.

Ok, Yes the bar jumps right where it should before I start. As soon as it starts it throws the bar. I will try some of the suggestions here. Thanks for the quick help and reply.

I would try to turn it way down, like others have said. if you can get it to just spin and it stays on then you are trying to start it to fast. start it really slow and then adjust from there.

mine doesn't work if i try it w/o a flask, it just gets thrown instantly.. my method that always works is i drop the stirbar in the flask, center it on the stirplate, make sure it is turned down all the way, turn on the stirplate, then very slowly turn up the Rheostat until it just starts to vortex..

Close the clearance as much as possible. You can also try to add more magnets.
Try slowing it down. For mine I had to add between 100 to 200 ohms in series with my rheostat. I forgot what my input voltage is.

Honestly, I think it all has to do with how well lined up the magnets and stir bar are to the center of the fan--that's where the tinkering comes in. If the magnets are placed properly, you should be able to use 12V input straight to the fan without a rheostat and let it rip without throwing the bar. Typically, the magnet(s) should be spaced about equal to or slightly longer than the stir bar you're using. I can post a picture of some of mine later, which might help you visualize the set-up with HD magnets.

I tried and tried to get it right with the HD magnet in one piece and I could eventually get a vortex but never to full power, especially full power right off the bat. Breaking the magnets in two and realigning them was the solution, IMO.

I used a HD magnet without breaking it and I can pull a vortex in a 1 gal jug all the way to the bottom. Maybe I just got lucky on placement, I don't know. But I would agree with Cram, others have reported good results using two magnets.

I have the opposite results from tknice...mine throws a 1" stir bar every time and works perfectly with a 2" stir bar. I use a 1000ml flask.

Hard drive magnets are not rectangular magnets, they are made into a arc. The magnets seemed strong enough but because of the way they are made you can't center the N and S poles directly across from each other without throwing everything off balance. When mounted with the N and S poles directly across from each other, most of the magnet weight will be to one side of center and this caused a serious vibration problem kind of like your cell phone buzzer but 10 times worse.

When you mount the magnet so the weight is balanced the N and S poles want to pull the stir bar off center towards the N and S poles. The stir bar won't pulled far off center but it is enough to cause the stirbar to throw at any speed but the lowest setting.

Either of these issues will cause your stir plate to throw the stir bar. You stir bar has to spin centered above the motor with as little as possible to pull it off center.

OK, I messed with the distance and get close. So next I think I'll try and break the HD magnet and see if that works. It looks so simple in the video.

So now, I adjusted the distance, I adjusted the Magnets, I lowered the input to 9V. I tweaked and played. Now at SLOW speeds it throws the magnet, Oh my… At full speed it runs fine, I can slow it down but not to the point it doesn’t make the vortex touch the bottom and add air. So why only when it runs slow does it throw? I have not tried to make a starter yet and I know the water is a different viscosity than starter. Any clues?

I had a lot of trouble with harddrive magnets. They would work, but wouldn't be very stable, even at the slowest speed. Sometimes I would wake up to find it had thrown the bar sometime during the night . I replaced them with these:

http://www.amazon.com/gp/product/B000SJMPU6/?tag=skimlinks_replacement-20

They work much better. Can start right up at 12V no problem and have never thrown the bar. I just put one on each side of the fans middle section. They even easily spin the bar in a 6.5Gal carboy.

My stirplate has a single hdd maggot. It will throw all stirbars > 7/8 inch at high speeds. A 1/2 inch - 3/4 inch stirbar works great through the whole range of speeds and is sufficient up to 1 gallon starters (haven't tried anything larger).

Thank you. Thank you. Thank you. I removed the spacers between my fan and the top of the project box and my stir bar spins like propeller, never gets thrown and I have a vortex that looks like someone pulled the
drain plug on the Atlantic Ocean! WOO HOO!