these are the stir plates i built, one that holds 2 5L flasks and one that holds 3 2L flasks..... I am having problems with the stir bar it comes to the middle and doesnt stir... any thoughts, its a real real strong magnet
My stir plate, and problems
- Thread starter Opherman47
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OP
OP
sorry for the foggy pictures its a humid day and the camera had been the air conditioned house, those screw heads are flush with the top btw
RegionalChaos
Well-Known Member
Have you tried different magnets?
OP
OP
no i have not tried different magnets... i did try this type of stir bar though the cross kind, the magnet i have is 3.8" x 7/8" by 1 7/8" and is very very strong.... perhaps i need a straight stir bar, maybe not.... lots of folks seem to be getting a single magnet to work however??? thoughts fellas? i am going to order 10 stirbars, so i would like to know if it will work with a stir bar before i place a bulk order, perhaps i can gain wisdom from yooose guys
mariojr
Well-Known Member
Test it with a paper clip to see if a straight stir bar would work. Also it seems to me that the plexi-glass could be keeping the magnet too far from the bar and can't produce enough pull to spin it. On mine the distance between the magnet and flask is very small and with no other material that could interfere.
OP
OP
the distance is very very small less than the top of a screw and the magnet is very strong
dstar26t
If it's worth doing, it's worth overdoing
Do the fans spin with the stirbar in place or are they stalled when you try turn them on?
OP
OP
the fans spin quite freely... the cross stir bar comes to the center and then stands up
wyzazz
Well-Known Member
Try moving the flask FARTHER away from the magnet. I suspect you may need more space between the magnet and stirbar. Mine has a really, really strong HD Magnet on it and I have to be around 1/2 to 3/4" away.
OP
OP
good thought!!! ill try it
camiller
Well-Known Member
If the stirbar in fact is standing up then I suspect the polarity of the magnet is not along the length of the magnet but rather through the face of it.
If you read the description of this one: http://www.gaussboys.com/ndfeb-magnets/B2506E-N42.html is says "Magnetized: Through 6mm thickness - poles are on the large rectangular surfaces" so if your magnet is like this one then the magnetic field is up/down rather than end to end.
You need to consider either getting two small magnets or finding a single magnet with the magnetic field oriented along the length. like: http://www.gaussboys.com/ndfeb-magnets/C0625.html
mariojr
Well-Known Member
Wow that's some awesome information. Who knew!
camiller
Well-Known Member
A lot of the folks that use a single magnet are using magnets salvaged from old hard drives. These arc magnets, at least the ones I have tried myself, are magnetized such that one pole is on the inside of the arc and the other pole is on the outside of the arc. See this page http://www.kjmagnetics.com/magdir.asp near the bottom where it says "Arc Magnetization with Poles on Inner & Outer Face".
dex0807
Well-Known Member
Mine uses an old magnet from a hard drive. Hard drives have two of these and they are very powerful, they will stick together and pinch skin. 
BadgerBrewer
Well-Known Member
I use an old hard drive magnet but when I remove the cover of my project box, sometimes the fan spins when I flip the power switch and sometimes it doesn't. With a little nudge from my finger it will then spin, but I wonder why is isn't consistent?
camiller
Well-Known Member
Mine uses an old magnet from a hard drive. Hard drives have two of these and they are very powerful, they will stick together and pinch skin.
yeah, pinched. However for bone crushing power:
http://www.geekologie.com/2009/02/guy_loses_finger_to_neodymium.php
Edit: note that the original site for this story has been taken over by some free energy type scammer. There are several blogs like the one I linked to above that still have the details but don't bother following through to the magnetnerd site.
OP
OP
man really really great information!!!
camiller
Well-Known Member
Hang Glider
Beer Drinker
your old hard drive magnets are interfering with the motor, which is an inductive coil -
try getting the hard drive magnet off the motor (use a spacer of some non-metalic design - a piece of plastic, wood, whatever. Of course, you may have to adjust the motor lower so it doesn't scrape your box or flask...
BadgerBrewer
Well-Known Member
That is most likey my problem. Great idea! Thanks for pointing me in the right direction.
OP
OP
ok my problem was the polarity, i now have my stir plate up and running.... thank you so much for your help everyone!!!
Edit: Should have read all the answer before posting.
Standing up! Just a thought, is the magnetic field vertical or horizontal? I wonder if your magnets are magnetized to have one pole on the top and the other on the bottom. That would make it stand up.
As the stir bar stands up, try to slide it back and forth on top of the magnet. It should attract at one end and repel at the other.
Sorry for going slightly off topic, but are you sure about HD magnets having polarization inside/outside of the arc? I have collected parts for building a stir plate, and I played around with the magnets a little trying to determine polarization. I thought that they were Magnetized through Circumference as shown at your link, that is, poles to the left and right. Great link by the way. The magnets were so strong that I ended up breaking them (mounted in pairs) so I had to butcher a second HD.
I suppose putting a stir bar on a magnet would show the situation, by the bar aligning itself with the magnetic axis.
I got a stir bar and put it on one of my hard drive magnets. I include a thumb nail link below that shows how it lined up. There are two arc magnets, one on each side of a wad of paper, so that I can separate them without too much force. Both are oriented identically, except that North and South align with each other. If I try to align the stir bar radially with the arc magnet, it snaps back to the position shown. It appears that my magnets are magnetized in a direction 90 degrees different than yours. Or did I misunderstand something?
camiller
Well-Known Member
I got a stir bar and put it on one of my hard drive magnets. I include a thumb nail link below that shows how it lined up. There are two arc magnets, one on each side of a wad of paper, so that I can separate them without too much force. Both are oriented identically, except that North and South align with each other. If I try to align the stir bar radially with the arc magnet, it snaps back to the position shown. It appears that my magnets are magnetized in a direction 90 degrees different than yours. Or did I misunderstand something?
No, you are understanding perfectly. Yours is 90 degrees different than mine. Kind of makes me wonder if people that have problems with hard drive magnet based stirplates consistently have one type of magnet or the other. Now I really need to get around to building mine.
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