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Wire a potentiomete in to a circuit

  1. Oct 17, 2006 #1
    i need to know how to wire a potentiomete in to a circuit. More specifically i am making a meagnetic stirrer and need to regulate voltage how would i wire the pot into the circuit.
     
  2. jcsd
  3. Oct 17, 2006 #2

    berkeman

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    To regulate voltage (if there is more than a few milliAmps involved), you should use a voltage regulator for the power element, and the potentiometer as the voltage control. Check out the datasheet for the LM317 adjustable positive voltage regulator -- it describes how to combine it with a potentiomenter to make an adjustable voltage regulator.
     
  4. Oct 17, 2006 #3
    thanks but i figured it out through trial and error
     
  5. Oct 17, 2006 #4

    berkeman

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    Did any of the errors make smoke or fire?
     
  6. Oct 17, 2006 #5

    Danger

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    Of course; it doesn't really count as an error otherwise. :uhh:
     
  7. Oct 17, 2006 #6
    no they didnt i used a 9 volt battery no sparks no nothing until i got the right circuit and the motor turned on. But i am disapointed at how hard it is to get the right voltage i need a very specific voltage to achieve a maximum vortex wich is around 5.6 volts. I've only been able to hit the sweet spot a few times in the last hour.
     
  8. Oct 17, 2006 #7

    berkeman

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    That's one of the reasons I suggested using an adjustable voltage regulator -- to get maximum power to the load. What voltage and current are the motor rated for? How long do you need to run it off of the 9V battery?
     
  9. Oct 17, 2006 #8
    its rated at 12v .15A. So how those this voltage regulator work exactly.
     
  10. Oct 18, 2006 #9

    berkeman

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    Then the motor will only run well at 12V. Can you use a 12Vdc wall adapter instead of the 9V battery?

    Here is some background info about voltage regulators. They are used to control an output voltate when supplied with a higher input voltage. To make a stable 12Vdc output, you would typically use a low-cost regulator that takes as an input something >= 15V, or a slightly more expensive "low dropout" regulator that requires an input voltage of something like >= 13V.

    http://en.wikipedia.org/wiki/Voltage_regulator
     
  11. Oct 23, 2006 #10
    I tried to build the same voltage regulator, but mine smoked real quick twice... I beleive that the LM317 is not the recomended voltage regulator for me, since I have such a large alternator!!
    I was mainly trying to control the voltage of my 320Amp alternator, that is externally rectified running to a series of 8V batteries to gain up to 20VDC for 5-10 second increments...

    I followed the easy shematics for the LM317 voltage regulator, and I think that there is too much voltage input that is causing the LM317 to blow... Is there a larger voltage regulator that will handle this type of voltage???

    Seems like there would be...

    Any help and info is appreciated

    Thanks
     
  12. Oct 23, 2006 #11

    berkeman

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    Whew, I thought I was in the Twilight Zone there for a couple seconds, hunter. Are you sure you popped into the correct thread? In your other thread about voltage regulators:

    https://www.physicsforums.com/showthread.php?t=139163

    I thought you were building the discrete parallel BJT regulator to handle your high power requirements. An LM317 is a regulator for a couple amps, not 320A.
     
  13. Oct 23, 2006 #12
    what do you suggest for a regulator from the input side of a 320 amp alternator???

    I tried the LM317 and smoked 2 of them....

    Please help, I'm banging my head.....
    lol
     
  14. Oct 23, 2006 #13

    berkeman

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    Have you tried the multiple parallel power BJT approach that I brought up in the other thread? You're going to need some honking big transistors (and lots of them) for a 320A regulator.
     
  15. Oct 23, 2006 #14
    Hello Berkeman

    Im gonna take a picture of my current voltage regulator so you can see what I am trying to re-build...
    I will post it in my initial thread...

    Thanks
     
  16. Oct 23, 2006 #15

    NoTime

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    For an altenator what you want to regulate is the current going to the field coil. Not the rectified output.
    Note that even the field coil will draw much more than an LM317 can provide.
     
  17. Oct 23, 2006 #16
    Also, the field coil (which is actually the rotor) has the current varied in it by pulse width modulation. The average current in it is maintained at a given level in order to maintain the desired output voltage under a given load.
     
  18. Oct 23, 2006 #17

    NoTime

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    I've never actually seen PWM used in an Auto alternator.
    It's certainly a viable option though.
     
  19. Oct 24, 2006 #18
    I don't think ANY of them can do it without PWM. The field current is too high to do it any other way.
     
  20. Oct 24, 2006 #19

    NoTime

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