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    Ridiculous Rheostats

    http://www.ocforums.com/showthread.php?t=312170

    I followed the instructions there to calculate which rheostat I need to get to control my 92mm nidec's, I wound up needed a rheostat about 4 ohms, 6.42W.

    After checking all the major websites, any that had some close enough were about $25-50. ridiculous.

    Anyway, is there any other cheaper way to do this? Each fan is 12v, 1.1A. One will be controlled independently from the other 2.

    #2
    Re: Ridiculous Rheostats

    Rheostat haven't heard that term in awhile. Gone the way of LPs and 8-Track tapes .

    They used to use them (among other things) as dimmer switches before triacs. As you probably can guess they heated up ALOT and I'm sure caused a few fires.

    This is quite simply the caveman way of reducing fan speed. Can't screw up installing a 2 terminal device .

    2 ways to do this:

    Voltage Regulation

    Pulse Width Modulation

    Voltage Regulation

    With the VR route you set up a variable voltage regulator (with a suitable heatsink rated for the total current draw of the 2 fans) tie 1 resistor and a POT (in a voltage divider arrangement) to the control pin and ground and you have a speed controller.

    The disadvantage of this is heat dissipated you also must make sure that the fan will start from a dead stop at your selected speed (voltage) and not stall. Since each fan model has a minimum voltage needed to overcome inertia. Once it's going it will continue this is a quick check and only needs to be done once.

    Also the speed range adjustment of the fan will be limited for the reason described above.

    Pulse Width Modulation

    Building this yourself isn't practical and would probably cost more than buying a PWM fan controller premade. Basically it switches the fan rapidly on and off from 0V to 12V to regulate it's speed.

    Check this link out about regulating DC fan speeds:

    http://www.analog.com/library/analog...fan_speed.html
    Last edited by Krankshaft; 07-26-2009, 12:24 PM.
    Elements of the past and the future combining to make something not quite as good as either.

    Comment


      #3
      Re: Ridiculous Rheostats

      Can you draw a diagram or something of the VR method?

      Any specific ratings I need to look for the voltage regulator, the resistor, and the pot?

      Comment


        #4
        Re: Ridiculous Rheostats

        By searching on LM317 I found a number of circuits, and component calculators for it. This guy has a 12V to 9V regulator using an LM317. With a few modifications you can have a variable speed control for your fans. The most important one - attach a heat sink to the LM317. I recall there was an earlier thread, but I don't remember what you want to do. The big choice - do you want the fans to run at a fixed speed, or do you want to adjust the speed easily. If you want an easily adjustable speed, get a 1K pot with a shaft and put a knob on it. Otherwise use a simple trimmer pot.

        PlainBill
        Last edited by PlainBill; 07-26-2009, 04:36 PM.
        For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

        Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

        Comment


          #5
          Re: Ridiculous Rheostats

          Originally posted by 370forlife
          http://www.ocforums.com/showthread.php?t=312170

          I followed the instructions there to calculate which rheostat I need to get to control my 92mm nidec's, I wound up needed a rheostat about 4 ohms, 6.42W.
          Is the 4ohm to be in series with the +12v line to reduce the voltage at the fan to something like 7v?

          If so, and assuming you don't need to adjust the fan speed, you could buy a 3.9 or 4.3 ohm 10W resistor and just wired it up. There are some wirewound resistors that can be chassis mounted so use your computer case as heatsink.

          Comment


            #6
            Re: Ridiculous Rheostats

            I think I am just going to break down and get a lamptron fc-2 controller. Does PWM with 4 channels at 20w each. blue led lit dials and a black finish in a 5.25" bay.

            Only 20 bucks too.

            Comment


              #7
              Re: Ridiculous Rheostats

              Originally posted by 370forlife
              I think I am just going to break down and get a lamptron fc-2 controller. Does PWM with 4 channels at 20w each. blue led lit dials and a black finish in a 5.25" bay.

              Only 20 bucks too.
              That would be gross overkill, but probably it would be cheaper than building one yourself. Even more so if you factor in the hassle of building it.

              PlainBill
              For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

              Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

              Comment


                #8
                Re: Ridiculous Rheostats

                Each one of these fans are 13.2W (1.1A). 110cfm nidec screamers.

                Comment


                  #9
                  Re: Ridiculous Rheostats

                  Originally posted by 370forlife
                  Each one of these fans are 13.2W (1.1A). 110cfm nidec screamers.
                  I prefer quiet fans. If I want screaming I can always complain about my wife's housekeeping.

                  PlainBill
                  For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

                  Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

                  Comment


                    #10
                    Re: Ridiculous Rheostats

                    >>If I want screaming I can always complain about my wife's housekeeping.<<

                    OUCH !!!

                    veritas odium parit

                    Comment

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