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-   -   Brand new stir bar lost it's magnetism? (http://www.homebrewtalk.com/f51/brand-new-stir-bar-lost-its-magnetism-368893/)

bduane 11-20-2012 01:06 AM

Brand new stir bar lost it's magnetism?
 
Just bought it a few hours ago. I've been playing with my DIY stirplate trying to find the right balance/distance for the magnets on the fan.

When I first started the stir bar would really stick right to where the magnet is and spin no problem at slow speed. But now, the stir bar barely wants to stay over the magnet when it's not moving. Add a little bit of rotation and forget it, it goes off to the side.

When I first bought it, I could easily test polarity by holding an end of the stir bar over the end of my hard drive magnet to see if it attracted or repelled. Now it seems to attract on both ends.

Is it possible that my hard drive rare-earth magnet was strong enough to demagnetize the stir-bar?

Misplaced_Canuck 11-20-2012 01:11 AM

It's a possibility, but doubtful. Are you spinning this in an erlenmeyer, or in a non-flat bottom vessel? Either way, try moving the container left-right, front-back and see if you can get it turning again.

MC

bduane 11-20-2012 01:15 AM

Erlenmeyer...

Shouldn't one end of the stir bar repel from one end of the hard drive magnet?

bduane 11-20-2012 01:23 AM

I think i did demagnetize it somehow. I read on how to "remagetize" a magnet, basically continuously pass 1 end of a strong magnet over 1 end of the magnet that needs to be magnetized and i did this for a while, and now it seems to repel again at one end.

dcarter 11-20-2012 02:26 AM

I have never seen a demagnatized stirbar.

bduane 11-20-2012 02:36 AM

Quote:

Originally Posted by dcarter (Post 4605314)
Stirbars aren't magnetic they are just an iron bar wrapped in plastic. The magnet is in the stirplate.

A stir bar (or flea) is a magnetic bar used to stir a liquid mixture or solution, usually in a laboratory. The stir bar's motion is driven by a separate rotating magnet or assembly of electromagnets (i.e., coils) located beneath the vessel containing the liquid.

After remagnetizing my stirbar by passing my rare-earth magnet over it repeatedly, it is now working great!


dcarter 11-20-2012 02:56 AM

Ha! Yeah, I did a quick search and found that my first post was incorrect. Great to see you have your stirbar back to normal!


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