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Magnetic Stirrer

  1. Jul 15, 2007 #1
    Hi i am trying to make a magnetic stirrer. I have seen tutorials on how to make a magnetic stirrer from a pc fan and magnets. i have actually constructed such a device, but the results I got were less than satisfactory. My problem is that the flea used to stir the solution doesn't want to spin. For some reason it keeps switching directions and makes a whole lot of noise, but doesn't spin continuously. Does any one have any suggestions on how to fix the problem or maybe a whole new design.
     
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  3. Jul 16, 2007 #2

    Integral

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    Just a guess, can you reduce the speed of your driving fan?
     
  4. Jul 16, 2007 #3

    chemisttree

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    Sometimes a spacer between the primary magnet and the flea will help. About 1/8" more should do it.
     
  5. Jul 16, 2007 #4
    I have a potentiometer but I don't exactly know how to wire it. I remember messing with it a few months ago but i hooked it up by trial and error. It has three prongs they're not labeled. If some one could explain how it works i will appreciate it.
     
  6. Jul 16, 2007 #5

    mgb_phys

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    The outer 2 pins are the ends of a resistor. The middle pin is a wiper which touches the middle of the resistor. With the knob at the extreme right it is near the right pin and so there is minimal resistance between the right pin and the centre. As you turn the knob to the left the esistance between the middle and right pin increases and the resistance to the left pin decreases. The resistance between the left and right pin is constant.
    Simply connect one of the outer pins to the the power supply, the middle one to the fan and the other side of the fan back to the other side of the power supply.
     
  7. Jul 16, 2007 #6

    Danger

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    I've never known how to use one of those bloody things either; I'd only used straight rheostats. Does the ground side of the fan connect to the 3rd pin of the pot? (Or, more accurately, are they both connected to the same side of the power supply?)
     
  8. Jul 17, 2007 #7

    Integral

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    2 ways to wire a pot:

    1. As a potentiometer, connect both ends of the pot to the power supply, then one side of the PS and the center tap to the load. As you move the wiper you will "select" a voltage (potential) from the pot, thus the name.

    2. As a rheostat, one side of the PS to an end of the pot, the other side to the load, center tap to the load. Note that one side of the pot is floating it is not connected to anything. With this arrangement you are varying the resistance in the circuit therefore controlling the current.
     
  9. Jul 17, 2007 #8

    Danger

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    Thanks, Integral. That will come in handy.
     
  10. Jul 17, 2007 #9
    Thank you Integral thats a lot easier than trial and error.
     
  11. Jul 17, 2007 #10
    Just wire it up works great Thanks a lot
     
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