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replacement 4 lead fan.

Discussion in 'General Electronics Discussion' started by davelectronic, Oct 15, 2015.

  1. davelectronic

    davelectronic

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    Dec 13, 2010
    Looking for some help with a 4 lead smps fan. I can only find replacement fans with 2 - 3 leads, its a 40mm 12 volt axial fan. Having tried 2 and 3 lead fans the psu wont power up, i have a working second unit identical, and have tried 2 and 3 lead fans on that. Its the same story, until i replace either unit with the one good 4 lead fan it wont power up. So i have one unit with a good 4 lead fan that powers up fine, the second unit needs a 4 lead fan to work, but i can't find one. My question is can i trick the unit to use a 3 lead fan, is there a way to site that fourth lead to a terminal or juction to get the 3 lead fan to power the unit on. Just a bit more info, these are 1200 watt converted served psu's model. HP1200 DPS FB. Thanks for reading.
     
  2. Martaine2005

    Martaine2005

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    May 12, 2015
    Hi Dave, that's an interesting question.
    I would like to think that the forth wire is a link internally to switch the psu on.
    Don't know which one though.

    Martin
     
    davelectronic likes this.
  3. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    Martaine2005 likes this.
  4. Martaine2005

    Martaine2005

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    I should have thought of that! Gryd3 posted on that a while back.
    That's what happens when 'one' doesn't pay attention..
    Perhaps you didn't look very far here is one..EBAY

    Martin
     
    Last edited: Oct 15, 2015
  5. davelectronic

    davelectronic

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    Dec 13, 2010
    Thanks for the link, i knew the 3 lead configeration, but that explains the fourth lead. The problem i have is no 3 lead fan will work, as the pcb and circuit is not getting feedback from any fourth lead. So i guess there is no easy answer. The 3 lead to 4 lead convertors i've used allow connectivity of the molex connector physically, but electrically pin 4 is rendered redundant. And in this application it will fail to power on with out a fourth lead physical and electrical connection. Picture below of the fan. IMG_20151015_210031936.jpg
     
  6. davelectronic

    davelectronic

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    Dec 13, 2010
    Thanks again for the link much appreciated. But i am in the UK just thought there might have been a 3 lead solution, as there avaliable everywhere.
     
  7. Martaine2005

    Martaine2005

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    May 12, 2015
    Ah, I thought you were looking for a replacement 4 wire fan as John gave a link..
    I would think you CAN trick it in to believing a voltage is there!
    You have the 'good' second unit with four wires. Work out which are the fan and then the other two wires by checking voltage and when that voltage is applied. It could be as simple as linking them together. But it will probaly run full speed rather than slow and speed up as designed to do..
    I am in Somalia, we have lots of those leads. None work on four wire fans....:)
     
  8. davelectronic

    davelectronic

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    Dec 13, 2010
    Yes i have tried with 2 leads fan, and again with 3 lead fan, yet it still wont power on. Its where, if at all possible to go with that fourth lead.
     
  9. Martaine2005

    Martaine2005

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    May 12, 2015
    OK Dave,
    I found this for you. Pay attention and you will be sorted. BTW, I am UK too...


    Martin
     
  10. davelectronic

    davelectronic

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    Dec 13, 2010
    Thank you for the tutorial, interesting. So this is what i have, molex connector from the pcb, this has four wires. My fan is 3 lead, if i connect all three that i can, leaving the fourth, if i ground the fourth it should power on, if only limited cooling speeds. If that's the case its ok as my load is lite, to what the unit is rated at. So ground that fourth wire from the molex connector, and this should allow use of a 3 lead fan at limited speed.
     
  11. Martaine2005

    Martaine2005

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    May 12, 2015
    Sory Dave, I am confused more than ever.
    You said to get a 4 wire fan working.
    Now you have a 3 wire fan wanting connection to a four wire molex connector?
    What bit don't I understand?

    Martin
     
  12. davelectronic

    davelectronic

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    Dec 13, 2010
    The original fan had 4 leads to a molex connector on the psu's pcb, that fan no longer works. So i have a 3 lead fan, and had to stick with the original molex connector (its tiny smaller than normal) this has 4 leads. When i connect 3 leads in the correct order the supply wont power on. I know it sounds odd, as its the psu end, not the fan end, but that fourth lead i think needs to see something. No fan will power up the supply its dead, unless i connect the other units 4 lead fan to it. Hope i've made some sense lol.

    Ps. The psu will not power on regardless of fan lead connections, it will only power on when i try the 4 lead fan from the second identical unit i have.
     
  13. Martaine2005

    Martaine2005

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    May 12, 2015
    Is this the back of your psu? There might just be a trick..

    [​IMG]
    Martin
     
  14. davelectronic

    davelectronic

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    Dec 13, 2010
    Yes it is, mine both have the resistor, and both powered up fine. But one unit has the dead 4 lead fan, and as such wont power on. Was you thinking the pwm blue unterminated lead might reside on one of the blade pads. There by allowing use of a 3 lead fan.
     
  15. Alec_t

    Alec_t

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    Could the original 4-lead fan have a 2-phase or 3-phase BLDC motor? That would be expecting pulsed power, not steady DC.
     
  16. davelectronic

    davelectronic

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    I think it does support pwm as the power scheme. So i still have no resolution to get a 3 lead fan to power the unit. I think the unit needs continuous feedback from the fan. As its used as a converted server psu, another option i can think of is transplant the entire circuit unit in a new enclosure and use a bigger 4 lead fan like the intel fans. These larger fans i can get hold of. But over all a large task for a modified power supply lol.
     
  17. Martaine2005

    Martaine2005

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    May 12, 2015
    Yes, exactly that. The forth blue feedback wire is fed to the base of an NPN transistor. If you can locate that and the pad it switches 'high', you may be able to solder a link between them..

    But your best bet is to just bite the bullet and buy a 4 wire fan.

    Martin
     
  18. davelectronic

    davelectronic

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    Dec 13, 2010
    Yes your right, its the avalability of the 4 lead fan that's the problem. The entire site on the pcb for that fan molex is smd components, it looks very complex. So in all probability i might recase the psu in a larger enclosure and use a similar power rated larger 4 lead fan (easier to obtain) its a bit more hasstle, but not to bad. Thanks to everyone that helped me here (-;
     
    Martaine2005 likes this.
  19. Martaine2005

    Martaine2005

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    Hey Dave, I just remembered....I read some old posts of yours a while back!!
    I do hope the 'culprits' that angered you are no longer?

    Martin
     
    duke37 likes this.
  20. davelectronic

    davelectronic

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    Dec 13, 2010
    In the past mate i never hold grudges against anyone ! Tomorrow's a new day, the old saying (-; Thanks again for all your help ! Appreciated.
     
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