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Multiples Fans - cooling system for Laptop

Discussion in 'General Electronics Discussion' started by nammy, Apr 20, 2016.

  1. nammy


    Apr 20, 2016
    I would like to build a laptop cooler with old computer fans i grabbed.
    If possible, would like to power them from USB (dont have usb3.0)

    My questions are here:
    - Should i mount them on parallel or series? i guess parallel to keep max voltage for each.
    - About amperage, should i use resistors? and where to put them in the circuitry?
    - how many fans max can i use as its powered by USB?

    All the fans are different tho... here are the specs:
    (All are 12v)
    - 0.06A
    - 0.08A
    - 0.1A
    - 0.14A
    - 0.15A
    - 0.17A
    - 0.27A

    If USB is not possible, i have an AC Adaptor 9v 300mA (so ill need resistor). Any help or the curcuitry is welcome, since i heard Amp is multiplied is using a parallel schema.

    thanks a lot, im an electronic beginner much.

    PS: I made a Schema, lets say i use only the 4 bigger fans. (order doesn't mean much). Could you tell me how to know what Resistor values to use? (if needed of course...) Thanks a lot!!!

    Attached Files:

    Last edited: Apr 20, 2016
  2. Alec_t


    Jul 7, 2015
    Check the voltage rating marked on the fans. Very likely they're12V fans, so might not be happy/efficient working on 5V from a USB port. You shouldn't need resistors.
  3. nammy


    Apr 20, 2016
    Hello and thank you,
    Is the Amperage shown on fans, the MAXIMAL ones they can handle?
  4. dorke


    Jun 20, 2015
    For 12V fans you should use 12V P.S.
    USB is only 5V.

    You have 2 possibility :

    1. Use an AC line Adaptor to 12V (current should be higher than the sum of all currents of the fans you connect).

    2. Use a DC to DC converter 5V to 12V

    In both cases you don't need any resistors.
    Last edited: Apr 20, 2016
    nammy likes this.
  5. nammy


    Apr 20, 2016
    Thank you for your answer. So the Current (Amperages) shown on fans is what they NEED to work properly. And it is not like LED, no need a resistor to lower that. So anything with more Ampers that the sum of all fans is ok. And the Volts are just what will make Fans turn as the correct speed.

    Everything is more clear now, thank you !
  6. duke37


    Jan 9, 2011
    A 12V fan running on 12V will take its rated current except for start up when it will be higher.
    A 12V fan running on 9V will run slower and use less current. Since the torque is proportional to the speed squared, then the fan will run easier.

    A power supply can usually provide more than its rated current for a second or so but if a fan has seized bearings then the current might be very high for along time.
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