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Electronics How to make fans run at 7v?

Discussion in 'Modding' started by talladega, 26 Mar 2009.

  1. talladega

    talladega I'm Squidward

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    Currently I have a fan controller but I always run my fans at about 7v so I want to just have a toggle switch to be able to switch the fans from full speed and 7v.

    These are the fans I will have hooked up to it. http://www.petrastechshop.com/12yalod1cafa1.html

    I will probably have 4 hooked up to it.

    How would I go about doing this? I have searched around and have found links but they are dead.
     
  2. veland

    veland Member

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    Just make a switch that switches the ground from the fan between ground from PSU and +5V from PSU.

    +12v - +5V = +7V

    Do note that fanspeed monitoring won't work when doing this
     
  3. cpemma

    cpemma Ecky thump

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    A much better way is to put a zener diode in series with the fan red lead, so keeping the speed monitor.

    [​IMG]

    I permanently undervolt my case fans by taking the wires out of the fan connector, cutting the red one and soldering in a zener with heat shrink to cover the joints. Then braid or plait the three wires and re-insert into connector. But to have it switched is easier.
     
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  4. jrs77

    jrs77 Well-Known Member

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    Do it this way, and you can have it all. Fanspeed readout and 12V - 7V switch.

    [​IMG]
     
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  5. jrs77

    jrs77 Well-Known Member

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    A simple controller-board would look like this. A simple thing like this would even be possible to do with a Dremel to engrave a PCB :dremel:

    [​IMG]

    Fans can be directly plugged in and regulated and fan-speed can be connected seperately to your mobo if needed/wanted.

    The PCB is 100mm x 50mm and the parts (switches, diodes, pcb, connectors) would be somewhere around 30 $.
     
  6. jhanlon303

    jhanlon303 The Keeper of History

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  7. talladega

    talladega I'm Squidward

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    I have a fan controller for that, but am limited with space so I wanted something small and simple.

    jrs77 or cpemma, could you make a small diagram that isnt a schematic. i always have trouble trying to read those.

    thanks

    also with having 4 fans hooked up to this switch will it not overheat and wreck the diode? each fan is like 3.3w at 12v.


    edit: thanks john, but I want to be able to switch from 12v and 7v. :)
     
  8. jrs77

    jrs77 Well-Known Member

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    [​IMG]

    Just cut the red cable of your fan and assemble the switch and the zener-diode inbetween. The switch either leads the current through the diode = 7V or don't = 12 V.
     
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  9. cpemma

    cpemma Ecky thump

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    Each fan wants its own 1.3W zener diode unless you can find a higher-wattage one; the 5.1V 5W one here would run up to 6 of those fans.
     
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  10. talladega

    talladega I'm Squidward

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    Ok, so if I use one 1.3W diode for each fan can I still hook up all 4 to a switch (thanks jrs77 for the pic!) and then if they are all going to the same switch how do i do it then?
     
  11. cpemma

    cpemma Ecky thump

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    Only if it's a 4-pole, 2-way switch. Or two fans to a more common 2-pole 2-way switch.
     
  12. jrs77

    jrs77 Well-Known Member

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    Like this, yes, with the switch cpemma mentioned allready. Otherwise you would shortcut the whole thing. Each fan needs it's own current-wiring.

    [​IMG]

    EDIT: Basically the switch is 4 in 1, having 12 pins.
     
    Last edited: 26 Mar 2009
  13. cpemma

    cpemma Ecky thump

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    You can simplify the switch to a plain on-off that shorts out the zener for the full 12V

    [​IMG]

    Also shows the 2-pole version, same principle for 4-pole.

    Need 1-pole per fan - the jrs77 drawing has all the zeners in parallel with the drawn 1-pole switch, and given normal voltage tolerances they'll blow in turn.
     
  14. jrs77

    jrs77 Well-Known Member

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    I edited it allready, as it wasn't too clear :hehe:
     
  15. talladega

    talladega I'm Squidward

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    Ok so these diodes and this switch and i'd be set?


    Just to make sure I've got this all figured out correctly this is how the 12V line would be wired up right?

    [​IMG]


    If that is all correct, then thank you guys for helping me!


    But I have a second somewhat related.

    I found this switch and was wondering if I could use it as both a power and reset button in one.

    As far as I understand it the switch rests at center and is only momentary (returns to center automatically) is either direction (up and down) and each direction is separate. If I am right then I could have one 'on position' set as power and one as reset. Am I right about this? If so that would be great and I would like to have the switches on the front of the case all look the same instead of some push buttons and then some toggles.
     
  16. jrs77

    jrs77 Well-Known Member

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    Yes, you got that right there. This'll work like a charm ;)

    For your second question... well... yes. Doable, but I won't recommend it, as you may reboot your system accidentally :hehe:
     
  17. talladega

    talladega I'm Squidward

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    Why would it accidentally reboot?
     
  18. jrs77

    jrs77 Well-Known Member

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    Don't know... while you are going to switch the fans from 7 to 12 maybe :hehe:
     
  19. talladega

    talladega I'm Squidward

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    Ok. Then I wont have problems. I dont have big sausage fingers. lol
     
  20. hydro_electric_655

    hydro_electric_655 Dremelly Dude

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    [​IMG]

    That would be much simpler. You don't need to have each fan on its own switch pole, you can simply parallel them into 1 line. You don't have to follow that diagram exactly, but you do need to make sure that the switch will bypass the zener diode allowing full power to flow. IMO this is the cheapest most simple solution. You can also use a properly sized resistor in place of the zener.
     

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