fan pwm

Discussion in 'General Electronics Chat' started by matty204359, Apr 19, 2011.

  1. matty204359

    Thread Starter Member

    Apr 6, 2011
    105
    3
    My mother board has a odd connector I was wondering if anybody had thoughts about it
    [​IMG]

    Why does the CHA_FAN1 header have +5 volts where the PWM pin should be? I thought that disconnecting the fan PWM pin runs the fan at full duty cycle.
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    It could be for a new type of 4 pin chassis fan.

    I have never seen 2 4 pin fan connectors.
     
  3. matty204359

    Thread Starter Member

    Apr 6, 2011
    105
    3
    do you suppose hooking up an standard PWM fan would be a bad idea?
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Here's the 2005 standard for 4-wire computer fans:
    http://www.formfactors.org/developer/specs/4_Wire_PWM_Spec.pdf
    Connectors and pinouts are shown on page 19.

    I'll speculate that the constant 5v is supposed to operate the fan at a reduced speed rather than using an actual PWM signal, which would take more hardware to incorporate than a fixed 5v level.
     
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