Stirplate build keeps throwing bar!?

Would an arced bottom on a 2000ml flask cause it to constantly throw a stirbar?
Or, should the bottom be perfectly flat to perform best?
Even at its lowest setting, it tosses a 1.5" stirbar...

Any ideas? Thx!

Have you tried nudging the flask around to see if you can find the right spot? Also, have you tried a 1" bar yet? I use 1" bars on my two liter e-flasks and they're plenty big enough...

Cheers!

I had lots of problems with mine throwing the bar. It ended up being the magnet configuration. I had to mount two magnets on the fan so each one would grab an end of the stirbar.

I would think that a curved bottom would make it more difficult to make things work well. Mine is temperamental with small starters,

Check your stir bar if it has a hub in the center put two O rings on the ends and try it.
The hub lets the bar floop back and forth until it is thrown off.

https://www.homebrewtalk.com/f51/stir-plate-magnet-404859/

You can get barbell shaped stir bars for a rounded bottom. I use a 1 inch bar in a 2000 ml flask and have a 2 inch that would always get thrown.

Sounds to me like you need to adjust your magnet situation.

Well, i tried moving the magnets, no difference. Then i tried using 2 separate magnets, still nothing. Im thinking it has to be the curved bottom. I used my coffee pot and it worked flawlessly, so that would point to the flask, right?

If you're using hard drive magnets, you may want to just get some better magnets. I tried about five different hard drive magnets in different configurations but never could get something that worked well and didn't throw my bar. I have a curved bottom on a couple of my flasks too.
Swapped out the magnets for some better ones though and now I have zero problems with three different stir bars even at full speed on a curved bottom.

I got tired off f'ing with mine, picked up one from homebrewstuff.com and couldn't be happier.... Great speed control, power for big starters, no issues and never wondering if it was still stiring. Now gonna use the computer fan on the e brewery control.

krazydave said:

If you're using hard drive magnets, you may want to just get some better magnets. I tried about five different hard drive magnets in different configurations but never could get something that worked well and didn't throw my bar. I have a curved bottom on a couple of my flasks too.
Swapped out the magnets for some better ones though and now I have zero problems with three different stir bars even at full speed on a curved bottom.

Click to expand...

Krazy,
What did you use other than HD magnets? I tried rare earth magnets from Harbor Freight ..

I used some "super magnets" from the local hardware store. They're rare earth and about 5/8" in diameter. I also double stacked them for extra strength.

I glued a big washer to the top of my fan also so that I could play with the positioning before I clued them down permanently.

Took a little tweaking and balancing, but it works great!

Thanks, did you reverse the poles when you put them down?

I doubt one could ever get a stir plate to work with both its magnets in the same polar orientation...

Cheers!

day_trippr said:

I doubt one could ever get a stir plate to work with both its magnets in the same polar orientation...

Cheers!

Click to expand...

Yeah, what he said!
With both poles the same, the stir bar gets shoved off to one side without it even being turned on. You definitely know when you need to flip one over.

Before I go and hunt down more rare earth magnets, what about using two, HD magnets spaced apart? One on each side of the main carrier washer. Overkill?

Here are a couple of things I found out while building stirplates...

Glue a wood spacer to the fan so the rare earth magnets don't interfere with the fan motor. By the time you put enough power to it to overcome the magnets it starts spinning too fast.

Stick your magnets to your stir bar before gluing them down, this gets the spacing and polarity correct.

Use a 6v power supply, a 12v will throw the bar unless you have a really good speed controller.