5v/off/7v FanBus Q??

Discussion in 'Modding' started by Icebreaking, Aug 13, 2002.

  1. Icebreaking

    Icebreaking Member

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    I have made a fanbus that does 7v/off/12v like from fanbus.com but i want to run my fans at 5v and 7v at the most.
    Can some1 tell me how to do it?
     
  2. DDsD

    DDsD @DDsD

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    Its not possible =)

    You need one of the voltage lines to be common out of the 3 poles, in a 12/7 arrangement, the 12v rail is common, in a 7/5 there are no common voltage lines.
     
  3. looktall

    looktall Working Class Doughnut

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    some fans wont run at 5v anyway.

    some will run at 5v if you give them a push start, or start them at a higher voltage and then switch them to 5v. and some will simply refuse to run at 5v.

    much easier to just stick with 7v. pretty much every fan runs at 7v. i've only come across one fan that wont run at 7v. it will run quite happily at 5v though. :p
     
  4. PostModern

    PostModern Angry Brewer

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    Icebreaking: Why not just make a rheostat? You can then have any voltage you like at the turn of a dial.
     
  5. OP
    OP
    Icebreaking

    Icebreaking Member

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    I didnt think it was. I guess ill have to make a rheostat then.
    Also all my fans can run at 5v with no starting probs.
     
  6. aXxeman

    aXxeman Member

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    It is possible, with two switches - one switching the + of the fan between the 12v and 5v lines, the other switching the - of the fan between gnd and 5v.

    That gives you 12/7/5/off, with the off position being with both + and - connected to 5v.
     
  7. OP
    OP
    Icebreaking

    Icebreaking Member

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    Yes there is that way, but i meant by useing one switch.
    Thats just too many switches for me.
     
  8. coolmach!ne

    coolmach!ne Member

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    Why would you want to run lower than 7 anyway ? 80mm fans pretty much don't make a sound @ 7v
     
  9. OP
    OP
    Icebreaking

    Icebreaking Member

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    Well my PSU makes 7.8v instead of 7v so maybe thats y they still sound a bit loud.
    Is there a way to lower the volts to about 7v, like useing a resistor or something?
     
  10. DDsD

    DDsD @DDsD

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    Yeah sure could i suppose :)

    but how are you measureing your 7V rail?
     
  11. OP
    OP
    Icebreaking

    Icebreaking Member

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    I measured it with a Multimeter. How do i work out what size resistor i need to use to lower volts to like 6.5-7v?
     
  12. antomathy

    antomathy Member

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    icebreaking clear your inbox please =)

    this is what i said anyhoo

     
  13. looktall

    looktall Working Class Doughnut

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  14. antomathy

    antomathy Member

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    thanks heaps for that =)
     
  15. OP
    OP
    Icebreaking

    Icebreaking Member

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    Hey looktall, do you think you can check out why my inbox says its full but there are no messages at all in it, i have tried clearing the tracing history and all that but it still thinks its full. Can you please fix this.
    Thanks
     
  16. looktall

    looktall Working Class Doughnut

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    no i can't fix it. i don't have those sort of super powers. :p

    what you need to do is set it to show "from the begining", then you will find that you have a whole heap of old PM's.

    you're allowed a total of 100, which includes inbox, sentbox and any other folders you may have created. clear them all.
     
  17. DDsD

    DDsD @DDsD

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    yeah... check the Sentbox particularly, you dont realise it until its too late, but they build up surprisingly quickly.
     
  18. Gnuthad

    Gnuthad Member

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    Using a single DPDT switch you can do exactly what you are wanting. Hook the middle prong on each side up to the fan, with the +5V up to a prong on one side and the diagonally opposite prong. Hook 12V up to one of the free prongs and 0V up the the last free prong.
    Cheap-ass ASCII diagram below.

    Code:
    +12V  |   |  +5V
    
    Fan + |   | Fan -
    
     +5V  |   | 0V
    
     

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