Need Help with my Fan Controller Project

Discussion in 'The Projects Forum' started by Iago Pereira, Oct 11, 2015.

  1. Iago Pereira

    Thread Starter New Member

    Oct 11, 2015
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    I've reached to this schematic, in wich I tent to have a pwm regulator in wich, as I increase the fan speed the lm3914 lights up more leds according to the fan's speed, and when I turn the turbo switch, the fans get a little 15v boost and the 555 on the left starts blinking 3 red leds, but im not sure of how functional this circuit is. Design_5 PWM.png
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Do you need the LEDs and do you need the Turbo switch?
     
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  3. AnalogKid

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    Aug 1, 2013
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    You have the raw IC4 555 PWM waveform driving the 3914 with no filtering. That won't work. The 3914expects an analog voltage input. Hang a capacitor on pin 5 to filter the pwm to an average DC value.

    IC1 Vcc should not come through a 1.2 K resistor. It should be powered directly from either the +15 or the +12, and its operation controlled by the Reset input.

    All ICs need power supply decoupling.s.

    ak
     
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  4. Iago Pereira

    Thread Starter New Member

    Oct 11, 2015
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    should it be like this? Design_6 PWM.png
     
  5. Iago Pereira

    Thread Starter New Member

    Oct 11, 2015
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    I dont need them, but I want them ahah
     
  6. TheButtonThief

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    Feb 26, 2011
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    R3 needs to much higher than 120Ohms, something more like 10KOhms
     
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  7. AnalogKid

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    T 1 is not a darlington, so I'd cap R3 at 1 K.

    ak
     
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  8. AnalogKid

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    Well, since there still is no filter at IC3 pin 5, then ....... no.

    ak
     
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  9. Iago Pereira

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    Oct 11, 2015
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    Then how do I do the filtering at pin 5? Just by connecting a capacitor from R7 to Ground?
     
  10. AnalogKid

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    R7 is not connected to pin 5, so I don't know what you are talking about. My suggestion is to add a capacitor from pin IC3 5 to GND. This works with R8 to form a crude lowpass filter.

    Why is the output frequency of IC4 so low? 100 Hz is near the operating frequency of the fan motors. The PWM frequency should be much higher than this. Also, a higher PWM freq will be easier to filter at the input to IC3.

    ak
     
  11. Iago Pereira

    Thread Starter New Member

    Oct 11, 2015
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    what changes should I do to the IC4 then?
     
  12. AnalogKid

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    Aug 1, 2013
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    As I said:

    1. Why is the output frequency of IC 4 so low?

    Also:

    2. What is the operating frequency an duty cycle at each end of the R10 adjustment range?

    ak
     
  13. Iago Pereira

    Thread Starter New Member

    Oct 11, 2015
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    1- I don't know, i adapted a circuit i found on the internet...

    2 I don't know also... I don't understand the pwm part of the circuit very well
     
  14. Sensacell

    Well-Known Member

    Jun 19, 2012
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    What kind of fans are you using? do they function correctly under PWM control?

    DC brushless fans (the majority these days) have a controller chip inside that commutates the motor coils, if you interrupt the power to the fan, (PWM) this controller can reset or become unstable.

    You need to test this.
     
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  15. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    The supply to IC1 is always present (12V or 15V) so the LEDs will always be blinking.
    Unless the LEDs are closely matched they will be uneven in brightness. It is better if they have individual current-limiting resistors.
     
  16. Iago Pereira

    Thread Starter New Member

    Oct 11, 2015
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    Thanks all of you for the information, I've finished the circuit :)
     
  17. wayneh

    Expert

    Sep 9, 2010
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    And, how is it working?
     
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