Powering PC Fans by DC Power pack

Discussion in 'The Projects Forum' started by Drivium, Dec 12, 2011.

  1. Drivium

    Thread Starter New Member

    Dec 12, 2011
    2
    0
    I have 2 12v PC fans and a 24v power pack. I intend to use this power pack to power the two of these PC fans. Will the 24v powerpack send 24v to EACH of these fans? Or will the power be distributed evenly sending 12v to each? I am currently using a 12v powerpack to power the both of these, but when I unplug one I notice the other speeding up...perhaps because the powerpack is only sending 6v to each? Also, the 12v powerpack is 700ma and each fan is rated ~0.4a-~0.5a (so the 700ma may be the reason).

    Can someone provide some clarity as to how this works?
     
  2. kutalinelucas

    Active Member

    Nov 20, 2007
    98
    0
    Applying 24v to a 12v appliance will do you no good and most likley burn both motors pretty quickly (thats if they start at all!). Applied voltage isn't split between appliences, but drawn current is. If you have two motors with a stall current (maximum amount of current a motor is likley to draw) of 400 - 500mA, you'll need a 12v; 1A supply to run both motors at full speed, although both motors will probably run quite happily at 350mA (each), but it all depends on your application and the speed and torque you require.
     
    Last edited: Dec 12, 2011
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    I'd suggest a 24V->12V switching power supply, also known as a DC-DC Converter.

    Running two fans in series sometimes works, but failure is frequent due to their design. They are brushless DC motors, so expecting one to "use" just 12V and give the other 12V to the next fan doesn't work.

    Getting a 24V to 12V supply, rated at 1.5 Amps or more will allow you to connect both fans in parallel, and get better efficiency as well as a longer lifetime from the fans.

    I wouldn't suggest a linear 24V->12V regulator, as the 12V is dissipated as heat (50% efficient). Switching supplies run in the 80-95% efficient range, with very little heat generated.
     
  4. magnet18

    Senior Member

    Dec 22, 2010
    1,232
    124
    What current is the 24V powersupply? and what is the project?
    If the current is high enough, you might be able to power something resistive (think lightbulb or something) to drop the first 12 volts, then power the fans in parallel off the remaining 12
    of course, you might still run into the problems with the fans

    this is to all the guys who know more about this stuff than I do, is it possible to create a "reference voltage", like, use 2 very large resistors between the +-24V, and connect the center to where the series wired fans meet?
     
  5. Drivium

    Thread Starter New Member

    Dec 12, 2011
    2
    0
    These are the fans: http://www.thermaltakeusa.com/Product.aspx?C=1165&ID=1735#Tab1

    And I am using them to keep an xbox360 console cool. Each fan comes with the option to use a thermal sensor to monitor heat and auto-adjust fan speed according to need. The 12v power pack I am using is dc current. Sounds like I may need a higher amp power pack since it's only 700ma and each fan at max draws 0.5a. A 12v 1a power supply should power both at full potential. Am I understanding this correctly?
     
  6. magnet18

    Senior Member

    Dec 22, 2010
    1,232
    124
    yep, that should work
     
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