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Trying to find a step down power module

Discussion in 'General Electronics Discussion' started by happirt, Aug 25, 2018.

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  1. happirt

    happirt

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    Aug 22, 2018
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,839
    Jan 21, 2010
    For controlling motor speed, a pwm controller will do the job far better.

    But sure, on those cheap buck regulators you can replace the trimpots with regular potentiometers. The most important thing is to wire them up correctly.
     
  3. happirt

    happirt

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    Aug 22, 2018
    Doesn't the pwm controllers convert constant voltage to "pulses"? Wouldn't I need a pwm fan with 4 pins & why do they perform better?
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,839
    Jan 21, 2010
    No, you can supply a motor with pulses and it will have greater torque at lower speed than if you limit the volage. This means it will start more reliably at slower speeds and be less likely to stall.

    Having said that, I've found that many 12V PC fans tend to start and run at 5V, and I'm using that exact method to run a very loud server fan more quietly. It really depends on both the fan and how slow you need it to go.

    When you remove the voltage control trimpot on the buck converter, you will need to note which pin is which (the wiper is the critical one). If you get the other two around the wrong way the control will be set to fastest when fully counterclockwise instead of fully clockwise.

    Oh, and you will need to make sure the replacement pot has a similar value, and has a linear taper (not logarithmic or "audio taper").
     
  5. happirt

    happirt

    6
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    Aug 22, 2018
    I have tried a cheap ebay pwm controller and my fan made whizzing sounds and the motor sounded like it was going on and off (i thought this was because of the pulses) so I was going to try a step down instead...

    Should I try a better pwm controller with 20khz instead?
     
  6. Aswinth Raj

    Aswinth Raj

    2
    0
    Jun 8, 2018
    Yes try a converter with much higher frequency. But I am not sure if that was the only reason make sure you are sourcing enough current for the motor. I would recommend to give LM2576 Buck converter a try.

    You can find more details on LM2576 here.
     
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