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regulate fan speed

Discussion in 'General Electronics Discussion' started by camilozk, Apr 7, 2015.

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  1. camilozk

    camilozk

    116
    4
    Apr 20, 2014
    hi!

    I am using a computer fan (12Volts - 0.68Amps) with a power supply (12Volts - 1Amp), and I would like to add a potentiometer in order to be able to regulate its speed. What kind of potentiometer should I use?

    Thanks!!!
     
  2. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    A potentiometer will not regulate its speed. You need feedback to regulate its speed. How many wires does the fan have?

    Bob
     
  3. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    Let's clarify here:
    Regulate - Control with some form of accuracy or unit of measure. (ie, RPM or Cubic Meter of Airflow per minute)
    You can adjust the voltage to the fan to control it's speed, but without feedback as mentioned previously, the best you can do is 'slow, medium, medium high, and high'.

    There are more details to follow... but I don't feel like typing it out again... so I'll quote this:
    https://www.electronicspoint.com/threads/old-pc-psu-fan-issue.273414/#post-1647671

     
  4. alex Chiu

    alex Chiu

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    3
    Apr 1, 2015
    If the fan is two pin(+and-), there is no way to control the speed. Add a resistor does not work.
    12V = full speed, 6V not = half speed. The toggle force is not stronge enought to make it rotate.
    You may redesign, add another fan or fans for the purpose.
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,396
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    Jan 21, 2010
    PWM can be used to control the shouted of many small DC fans. Regulation, as mentioned above, strictly requires feedback. However if the fan is used as they typically are, the load on them does not vary much, so you may not require feedback (many fans speed controllers do not)
     
  6. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    You are right, 6V does not equal half speed, but it also does not equal full speed.
    The third wire typically found on computer fans is simply a sense wire that can be used to monitor the current speed. PWM to the fan can adjust the speed.
    Additionally, some fans have a 4th wire dedicated for this purpose to you leave a constant 12V on the power pins, and control the fan with a PWM signal on the control pin.
    In either case, there is a wire used for feedback because even with 50% duty cycles on PWM the fan may not be running at half it's normal RPM.
    Of course, some fans will refuse to begin to rotate if the voltage is too low, but once they begin to spin they can usually continue with no further interruptions.
     
  7. camilozk

    camilozk

    116
    4
    Apr 20, 2014
    great feedback, thanks!

    the fan has 3 wires. red - black - white

    IMPORTANT - I am not using the fan in a computer. I am using as I said the fan and a power supply. I use it as an additional fan below my computer when I process real time video. then:

    "You can adjust the voltage to the fan to control it's speed, but without feedback as mentioned previously, the best you can do is 'slow, medium, medium high, and high'."

    This is what I want: 'slow, medium, medium high, and high'

    So how to achieve that?


    thanks!
     
  8. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    Try some series resistors about 10Ω and 5W and see what speeds you get. Find a four way switch to select the resistor in the resistor chain.
     
    Gryd3 likes this.
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