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Old 01-06-2009, 08:34 PM   #91
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Because they are not centered?
Well, using two magnets I don't think its quite that easy, especially with odd shaped HD magnets. What your shooting for is the magnetic field produced by the pair of magnets to be such that it holds the stir bar in the center. It could be that the neg or the positive is giving a stronger pull and is grabbing the stir bar towards one side or the other.
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Then that means dumping your beer because you think it's bad is tantamount to abortion! And as Big Kahuna says, drinking a beer too soon is tatamount to beer pedophilia...
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Old 01-06-2009, 08:39 PM   #92
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That is exactly one reason I think I'm going to get some new magnets from McMaster. I'll give it one more shot before I do that though

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Old 01-06-2009, 09:31 PM   #93
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Well, using two magnets I don't think its quite that easy, especially with odd shaped HD magnets. What your shooting for is the magnetic field produced by the pair of magnets to be such that it holds the stir bar in the center. It could be that the neg or the positive is giving a stronger pull and is grabbing the stir bar towards one side or the other.
Worked fine for me, but I did not use Hard Drive magnets. They are nearly perfectly rectangular and click together end to end in a symetrical fashion.

Also, the distance between my magnets and the top can be measured in 32nds, sounds like he has too much air space on top and is losing pull. I have no problem at all spinning a two inch stir bar in my 2L flask.
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Old 01-06-2009, 09:47 PM   #94
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Worked fine for me, but I did not use Hard Drive magnets. They are nearly perfectly rectangular and click together end to end in a symetrical fashion.

Also, the distance between my magnets and the top can be measured in 32nds, sounds like he has too much air space on top and is losing pull. I have no problem at all spinning a two inch stir bar in my 2L flask.
Interesting... Maybe I'll source some longer machine bolts and give it a try...
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Old 01-07-2009, 12:04 AM   #95
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Ok, I used bolts that allow me to position the flask almost directly upon the magnet. Now the resistance from the stirbar/liquid isn't allowing the fan to spin (or is allowing it to spin very slowly). I think I need to get stronger magnets and try again...

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Old 01-07-2009, 12:13 AM   #96
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Ok, I used bolts that allow me to position the flask almost directly upon the magnet. Now the resistance from the stirbar/liquid isn't allowing the fan to spin (or is allowing it to spin very slowly). I think I need to get stronger magnets and try again...
How wide is your magnet? If I used a 3/4 wide magnet (it's 3/8 tall), I have the same problem. Mine are only 3/8 wide.
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Old 01-07-2009, 12:39 AM   #97
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I'm using a hard drive magnet which is approximately one inch long and is curved.

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Old 01-07-2009, 01:26 AM   #98
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Default Not wired right?

When I wire the fan red wire to the inside terminal of the potentiometer, and the input hot wire from the power supply to one of the outside terminals, the fan never turns comptetely off. I can adjust the speed, but it never gets below a certain rpm. However, if I wire the negative power supply wire and the ground wire for the fan to the other outside terminal, it turns off, but the potentiometer gets extremely hot. What's going on? Any guesses?

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Old 01-07-2009, 01:44 AM   #99
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When I wire the fan red wire to the inside terminal of the potentiometer, and the input hot wire from the power supply to one of the outside terminals, the fan never turns comptetely off. I can adjust the speed, but it never gets below a certain rpm. However, if I wire the negative power supply wire and the ground wire for the fan to the other outside terminal, it turns off, but the potentiometer gets extremely hot. What's going on? Any guesses?
Yeah, if I understand what your doing correctly.

Wired power supply to the input (one side) of the potentiometer, and the fan red wire to the output (center) then ground of power supply to ground of the fan is the correct wiring. You won't be able to turn off the fan using the pot, that is why you need to also include a switch.

What your doing the other way, if you were wiring red wire to the inside terminal and having grounds go to the other outside terminal is using the pot as a direct short to ground of your power supply, effectively making it a zero voltage at the fan, shutting the fan off. That is why the pot got so hot...bad idea.
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Then that means dumping your beer because you think it's bad is tantamount to abortion! And as Big Kahuna says, drinking a beer too soon is tatamount to beer pedophilia...

Last edited by Jonnio; 01-07-2009 at 01:50 AM.
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Old 01-07-2009, 06:20 PM   #100
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Originally Posted by NewBrew75 View Post
When I wire the fan red wire to the inside terminal of the potentiometer, and the input hot wire from the power supply to one of the outside terminals, the fan never turns comptetely off. I can adjust the speed, but it never gets below a certain rpm. However, if I wire the negative power supply wire and the ground wire for the fan to the other outside terminal, it turns off, but the potentiometer gets extremely hot. What's going on? Any guesses?
This is the reason I chose a 12VDC switch that was labeled for this build. It takes all the guess work out of wiring this beast. The inside terminal should ALWAYS be the "load" of the switch. The outside terminals are going to be your "supply" and your "earth (ground)".
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