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Old 11-24-2010, 04:05 AM   #1
stockwes
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Default Home made stir plate questions

I am looking at making a stir plate. I was going to use a coffee can for the housing. I was going to mount a 120mm fan in side near the top attached to a speed controller and use an old 12volt plug in from a old toy.

I am fine on the construction and electronics part but i am a little confused on the magnet part. I know i want a rare earth magnet but how strong? I would rather not use old hard drive magnets, i want something a little less jury rigged.

Would these work?
http://www.rare-earth-magnets.com/p-52-nsn0703.aspx

Thanks for any opinions and/or help

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Old 11-24-2010, 04:11 AM   #2
cyberwollf
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Are you wanting to use these inside as the stir rod or just mounted to the fan? I just used cheap Lowes magnets and $15 stir rod off ebay

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Old 11-24-2010, 04:12 AM   #3
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Or maybe these?

http://www.amazon.com/Neodymium-Magn.../dp/B001KUOKPA

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Old 11-24-2010, 04:52 AM   #4
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i was looking for something to use mounted to the fan. I have several of the Teflon coated stir bars that are about an inch long left unused from a bunch of chemistry supplies i had to buy in college as well as unused pyrex flasks but the actual machine is all i am missing.

I have everything else but the magnets for the fan and i want it to work good so i am willing to throw down $20 or so to put 2 or 3 together...

Iggie, the magnets you listed are a lot weaker than the ones i was looking at, is that all it will take? The ones i found have ~8 lbs, the ones you show are only like 1.5 lbs of pull?

Thanks for the help!

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Old 11-24-2010, 05:15 AM   #5
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My appologies. I didn't even look at the lbs of pull.

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Old 11-24-2010, 05:48 AM   #6
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does anyone know how much is necessary to function properly? Mabee 1.5lbs is all that is needed? I really have no idea...

Any help?

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Old 11-24-2010, 06:44 AM   #7
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Don't hate on the hard drive magnets! They have pull pounds to spare and are free, free, free.

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Old 11-24-2010, 12:36 PM   #8
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I hate trying to use hard drive magnets. They are typically of irregular shape, difficult to center and difficult to balance properly. The rare earth magnets are relatively inexpensive; not free, but not very costly either.

IMO, you need some fairly strong magnets for the best performance. I've been using some very strong rare earth magnets. You can vary the magnet pulling force by adjusting the distance between the magnets and the stir bar. The magnetic force is inversely proportional to the square of the separation distance. This means that a small change in the gap will result in a substantial change in the magnetic force. So, get some bad a$$ strong magnets and adjust the gap as needed.

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Old 11-24-2010, 01:43 PM   #9
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I have bought neodymium magnets from http://www.rattlesnakemagnets.com. I found them through ebay but you can buy direct from their website. They offer several different shapes and sizes for reasonable prices.

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Old 11-24-2010, 04:02 PM   #10
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i set my flask on top of a upside down tupperware that has the fan under it. I dont know the exact seperation disance, but cheap round lowes magnets work fine.

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