What stir bar for yeast starter on stir plate?

[petrolSpice]

I made a typical DIY stir plate. Instead of using harddrive magnets I used some powerful neodymium magnets I had at work. I got a set of four octagonal magnetic stir bars (50mm, 40mm, 27mm, 20mm) with the center balance band things on eBay. Only the two large ones work, the small two won't even center on the magnet.

They worked fine when I tested it with a stainless pot, but now I'm using a 5L flat bottom flask and it wants to throw the stir bars at any speed but the lowest (3V on a 12V fan). I removed the center band from the 40mm bar to see if it would help and now that one won't work at all

So I'm currently using the 50mm bar on the very lowest settings. It can just barely keep a dimple in the surface of the wort. And it clanks around like its off balance or something, like it might get thrown any second, but it hasn't thrown it yet in about 15 minutes.

Anyone had a similar issue? What stir bar should I try next? Looks like it needs to be at least 40mm to center on my stirplate's magnet.

 

[flars]

This document may help solve your dilemma. I use a two inch octagonal like yours, but also the one inch Spinplus.
From the article:
"For optimum efficiency and magnetic coupling the distance between the
magnetic poles of the drive magnet and the length of the stirring bar should be equal."

My octagonal bar tips and clacks as it spins, but it stays centered. With some yeasts the krausen is to heavy to allow for a vortex throughout the process, but I can still hear it spinning. The Spinplus is quiet.
I use a plastic Rubbermaid container for my starters. I don't know if this can create a performance difference though.


https://www.sigmaaldrich.com/conten...ich/General_Information/1/labwarenews-3-1.pdf

Found this article also.
http://www.novatech-usa.com/core/media/media.nl/id.353870/c.ACCT119126/.f?h=48e04331a8b0ae4b8295

 

[seabass07]

Sounds like the magnets aren't strong enough or are too far away. I'm also using neodymium magnets on mine. I'm using 8 small ones total. 4 stacked on either side. I use a 2" stir bar. I don't get a full vortex, but plenty of stirring. I have a 3" bar, but the fan and magnets aren't powerful enough for them.

Actually, I just re-read your post. Are you using a single magnet? The stir bars have magnets on either side, so you need 2 magnets minimum.

 

[petrolSpice]

Thanks for the replies. The magnets I used are about 1cm cubes, I used 4 of them in a line to make a 4cm long magnet. They are quite powerful. On the counter (outside of water), I can turn the stir bar from 5-6" away, very impressive.

Here are some pics of what it's doing now. This is the best vortex I can achieve. It's a big starter, 4L.

 

[seabass07]

That's plenty of motion. But since the bars are magnetized on either end, I think you'll have better luck stacking them 2 high and positioning them where the magnets are on the bar vs laying them end to end.

 

[petrolSpice]

That's plenty of motion. But since the bars are magnetized on either end, I think you'll have better luck stacking them 2 high and positioning them where the magnets are on the bar vs laying them end to end.

Check out this link: http://www.kjmagnetics.com/blog.asp?p=stir-bars

Do you mean setting up my magnets like the bottom image? Mine are currently setup like the top image with the 4 cube magnets placed end-to-end. I'm hoping not to mess with the magnet orientation, it's all glued together and was a pain to get centered on the fan.

I'm curious if getting a rare earth magnet stir bar would help. The SpinPlus looks like it might work as well, at least to keep the clanking down.

 

[seabass07]

Exactly. I went through a few configurations before setting it up like that. It works great now. I'd need a much more powerful fan to throw the bar.