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  • help with fans

    I have installed a 5v 25x25mm fan and it's very noisy. I would like to drop the voltage to make it spin slower. how would I do that?
    second issue is how to filter fans to reduce interference? the more fans I'm installing the more interference I have on the lcd.

  • #2
    your building a all-indash setup right?

    you should be able to use resistors to drop how much voltage gets to the fan. just connect in series with the red wire, or in series with the black wire. if you have a radioshack nearby, they have a assorted 1/4w, or 1/2w resistor kit that would be perfect for this.


    with the interferance issue, i assume your using the pc power supply to power the fans. i wonder if you connect the fans to their own buck- voltage regulator to separate them from the pc components. the second idea is to use RF chokes, or different vga cabling for your screen..

    but if you have a all-indash setup, i wonder if the interference is due to the close proximity of the fan/screen. in this case, you might need to look into shielding the pc components.. an easy way to test for this would be to connect the fans to a external power supply, and see if you still have the issues..
    My OLD 2001 Mitsubishi Eclipse GT:
    "The Project That Never Ended, until it did"


    next project? subaru brz
    carpc undecided

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    • #3
      Interference from the fans cannot be RF, either it's magnetic interference from the coils and magnets, but again, i never seen an circuit sensitive to this at all (except from an old CRT monitor tube) but more likely yout supply voltage is jumping up and down a bit, so you need to add some capacitors on the 12 volt line rail you use for powering your LCD (and fans) and that should help with your problem.

      Start out with something like 4700 to 10000 uF/25V and see how it goes.

      // Per.

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      • #4
        ^ in line with the thinking that he is using a super-compact in-dash pc, and is powering the fans, pc, and screen off the same 12v rail of his dc-dc psu, wouldn't he also need to add a diode to the + line before the capacitor to prevent the capacitor from back feeding into the pc components?
        My OLD 2001 Mitsubishi Eclipse GT:
        "The Project That Never Ended, until it did"


        next project? subaru brz
        carpc undecided

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        • #5
          Originally posted by soundman98 View Post
          ^ in line with the thinking that he is using a super-compact in-dash pc, and is powering the fans, pc, and screen off the same 12v rail of his dc-dc psu, wouldn't he also need to add a diode to the + line before the capacitor to prevent the capacitor from back feeding into the pc components?
          Eh, No.

          Think of the power supply, it has capacitors on all the rails, it isn't back feeding anything. The Mobo has capacitors on the supply lines too.

          Adding a diode is just asking for trouble and getting an unwanted 0.4-0.6 volts drop in the voltage.

          // Per.

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          • #6
            doh... completely forgot about those caps, and should've remembered the diode voltage drop.
            My OLD 2001 Mitsubishi Eclipse GT:
            "The Project That Never Ended, until it did"


            next project? subaru brz
            carpc undecided

            Comment


            • #7
              Originally posted by zapro View Post
              Interference from the fans cannot be RF, either it's magnetic interference from the coils and magnets...
              Er, that's called RFI - eg, EMI, EMC etc.

              It is electromagnetic interference. (Can you separate them?)

              Note too - small DC fans (as used in PCs) are usually AC....

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              • #8
                the problem it was at one of the fan power plugs on the mobo causing the interference(on the Intel Atom 230 mobo, the side one). when I have unplugged that fan the intereference stopped. so I played with speedfan, dropped from 50% to 20% and the interference it's gone.
                now I have to deal with the voltage drop from 5V to something adjustable to see at which rpm would work better? any ideas? couple of diodes in series maybe? pot would be a much better solution.
                the fan is a 5V fan.

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                • #9
                  As soundman98 said, the usual way is with a resistor, depending on the fan and required speed you may need a couple in parallel or a 1watt resistor if they get too hot.

                  Depending on what the fan cools, where the PC is mounted and the environment itís in it may not be in your best interest to slow the fan too much.

                  The fan should not be causing interference and by slowing it you may be masking a future problem.
                  Have you tried another fan to see if the interference stops?
                  Palm sized ainol MiniPC, 8" Transreflective PRO, Win10, Reverse camera, Dual 10HZ GPS RX's for Speed Display & Sat Nav, FM-DAB & Phone Modules, iDrive interface. T-Screen HVAC control, custom microcontrollers, microcode and FE.

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                  • #10
                    the interference it's gone by switching two fans(gpu with cpu) and by lowering the % in speedfan.
                    this fan it's cooling the hdd only.
                    I have another 25mm fan, I can try that too.
                    my problem is that I'm afraid that when all mounted it will be to noisy.

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                    • #11
                      The problem is fans should not really interfere with the LCD. It indicates that something is not right. I run 5 fans and some are reduced in speed using resistors, one to reduce noise and others simply because they only need to move a small amount of air for the intended purpose, when running at full speed none cause interference even if the Screen is mounted on top of them.

                      I can see your problem with acoustic noise from the fans if the unit is mounted in the dash and therefore the need to reduce the speed and noise. However the interference to the screen is a separate problem. The noise may be caused by a supply rail starting to fail due to load or some other fault, there may be a problem with the LCD or the way itís powered or wired (factory connections like a missing earth).

                      IMHO if it was my system I would want to know why it has interference. Have you tried connecting a laptop to the video input of the LCD, leaving the LCD powered by the CarPC. Then try it the other way, powering the screen from a source completely separate and isolated from the car. This may tell you how the noise is getting in. Via the DC supply or the PC video interface. If it's the DC connection then you may just need a filter (perhaps the LCD doesnít have one internally). If the fans can cause interference now I would be willing to bet that it is only a matter of time before interference appears again after the complete system is installed and buttoned up in the car.

                      I am of course assuming the screen has an earthed metal cover enclosing the back of the LCD PCB.
                      Palm sized ainol MiniPC, 8" Transreflective PRO, Win10, Reverse camera, Dual 10HZ GPS RX's for Speed Display & Sat Nav, FM-DAB & Phone Modules, iDrive interface. T-Screen HVAC control, custom microcontrollers, microcode and FE.

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                      • #12
                        Originally posted by Mickz View Post
                        I am of course assuming the screen has an earthed metal cover enclosing the back of the LCD PCB.
                        even in the stock bezel, AFAIK, none of the lilliputs have this.... using the stock plastic bezel should allow for some limited distancing from the EMI source, but that doesn't account for much..
                        My OLD 2001 Mitsubishi Eclipse GT:
                        "The Project That Never Ended, until it did"


                        next project? subaru brz
                        carpc undecided

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                        • #13
                          Thanks for the heads up on that as itís a ďpossibleĒ source of interference if the video controller is in VERY close proximity to noisy wiring, it would have to pretty bad noise though. Iím used to open frame designs with a metal cover.
                          Palm sized ainol MiniPC, 8" Transreflective PRO, Win10, Reverse camera, Dual 10HZ GPS RX's for Speed Display & Sat Nav, FM-DAB & Phone Modules, iDrive interface. T-Screen HVAC control, custom microcontrollers, microcode and FE.

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