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  1. #1
    Member cetoole's Avatar
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    Guide to the 7v Fan Mod

    Many people, while desiring high performance out of their computers, decide that their computer is too loud, so the easiest way to combat this problem is to slow down the fans, which are the major noisemaker in the average computer. To slow a fan down, one must reduce the voltage powering it. The fans that most of us use in our computers are 12vdc fans, but most will run fine at lower voltages, with some going all the way down to 4v without issue. The cheapest and easiest way to slow down a fan is to simply power the fan off a different rail than normal.

    Now, most people know that the average computer has a +/-12, +/-5, and 3.3v rail, and it is simple to power fans off of these rails by changing the power lead for the fan from the normal 12v to the 5v rail, as most fans won't start with 3.3v. While these rails are common knowledge, many people don't know that there are also several "virtual rails", the 8.7v, 7v, and 17v, as well as the 24v and 15.3v rails. These rails are not true voltage rails, they are accessed by using one of the real voltage rails instead of the common ground as a ground for that rail, so the 12v=12vrail+ground, 5v=5vrail+ground, and 3.3v=3.3vrail+ground. Now, if you switch the ground to one of the lesser voltage rails, such as the 12vrail+5vrail, you end up providing 7v, which is the popular 7v fan mod. This is by far the most common, because the 4-pin molex connectors used to power devices such as hard disk drives and DVD ROM drives has a 5v line, 2 grounds, and a 12v line. To get 8.7v, it is necessary to bring a wire from the 20 pin ATX connector on the mobo, which is much less convenient. The voltages above 12v simply use the negative rails, but again, these are only found on the 20 pin ATX connector, and are not really very safe to use for this purpose, as the negative rails are very weak, and don't have enough load to absorb the power sent back up the rail.

    This is also an issue with the 7v and 8.7v mods, but much less so because of the load of the whole computer that is much greater than the load of the fans, but before doing this mod, always check. It is not a good idea to try this mod when starting a PSU with the wire trick, because unless you are running other things with it, there is no load, and you can cause physical damage to your hardware. Some of the lower quality PSUs also die with this mod, so it is only advisable to do it with a decent PSU.


    12v to the fans:


    7v to the fans:


    5v to the fans:
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    Last edited by Bobnova; 05-08-12 at 07:49 PM.

  2. #2
    Member Bobtod's Avatar
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    Excellent guide cetoole

    Also with the 80mm fans that have a molex pass-through connection, you can swap the pins over using a watchmakers screwdriver for a quick 7v mod without the need for any soldering as shown below:

    bt

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  3. #3
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    Excellent guide
    Thanks

  4. #4
    Member thegreek's Avatar
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    HERE is an easier guide.
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  5. #5
    Member stang8118's Avatar
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    Great guide! Gonna save me from searching the forums later! Going to be doing 7v mod when i get home.

    But what about the fans w/3 pin connectors? Are they moddable? Or is it for only 4 pin molex connectors?
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  6. #6
    Good guide
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  7. #7
    Member cetoole's Avatar
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    Quote Originally Posted by stang8118
    Great guide! Gonna save me from searching the forums later! Going to be doing 7v mod when i get home.

    But what about the fans w/3 pin connectors? Are they moddable? Or is it for only 4 pin molex connectors?
    3 pin fan connectors are only the 12v, ground, and tach signal, so you can't directly mod them. You can however use a 4 pin molex adapter to do the mod, just switch the correct wires on that and plug the fan in.

  8. #8
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    noted.

  9. #9
    Member dAvies.lOcker's Avatar
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    I am really struggling with this mod. The main sticking point is that i can for the life of me remove the molex pins enabling me to do the actual mod

    What is the best way, i've tried using a biro, but that isnt working....whot should i be "aiming" for - i see the little barbs but cant get to them/make them budge.

    Any help?

    D.L

  10. #10
    Member cetoole's Avatar
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    Quote Originally Posted by dAvies.lOcker
    I am really struggling with this mod. The main sticking point is that i can for the life of me remove the molex pins enabling me to do the actual mod

    What is the best way, i've tried using a biro, but that isnt working....whot should i be "aiming" for - i see the little barbs but cant get to them/make them budge.

    Any help?

    D.L
    Im not sure what a "biro" is, but when I remove the molex connectors, I usually use something like a dental pick or very thin screwdriver to push the pins in. Once the locking pins are flush in, it is easy to slide the whole pin out of the plastic housing. Is this a male or female molex you are having trouble with?

  11. #11
    biro is a pen.

    you have to find one that is big enough to get all the way over the pin, but is snug enough on the pin it will squeeze the tabs in. it took some rummaging in my desk drawer, but i eventually found one that worked perfectly.

  12. #12
    how do you keep the wire to stick in permanently? the wire seems to slip out kindda easy.
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  13. #13
    Member cetoole's Avatar
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    Quote Originally Posted by warlock110
    how do you keep the wire to stick in permanently? the wire seems to slip out kindda easy.
    I assume you mean after removing the pins, so it is quite easy. Before putting the pins back in, you just stretch out the barbs which hold the pin in the housing.

  14. #14
    Quote Originally Posted by cetoole
    I assume you mean after removing the pins, so it is quite easy. Before putting the pins back in, you just stretch out the barbs which hold the pin in the housing.
    i mean the fan wire that you connect to the pin lol, all i see is that people simply insert the wire in the appropriate hole, but how does it stays there. NVM, i see that you guys have a 4 pin plug, i'm using a 2 pin fan and i'm trying to make it simple by just sticking the pin in the hole.
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  15. #15
    Member T1Cybernetic's Avatar
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    Cheers for this i already know how to do the mod but i've right clicked and saved the
    pics for future reference because my brain sometimes packs up on me and i forget alot!

    Thanks again, great guide!
    Last edited by T1Cybernetic; 01-12-07 at 07:58 AM.
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  16. #16
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    which is the best voltage to connect the fans on ? 5V? 7V? 12V?
    also, which give the most performance/results ?
    Thanks.
    I have no ideas on these

  17. #17
    Member SolidxSnake's Avatar
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    higher voltage = faster...

    so 12v is faster and more airflow, but may be to loud on some fans.

    That is why people 5v and 7v their fans...

    the standard 3-pin fan connector is a 12v connector
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  18. #18
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    Quote Originally Posted by Bobtod
    Excellent guide cetoole

    Also with the 80mm fans that have a molex pass-through connection, you can swap the pins over using a watchmakers screwdriver for a quick 7v mod without the need for any soldering as shown below:

    bt


    Is this 7V mod ( the second picture ) ??

  19. #19
    Member cetoole's Avatar
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    Quote Originally Posted by texp4
    Is this 7V mod ( the second picture ) ??
    Yes

  20. #20
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    I want to ask a question:

    Example:
    YS Tech 120mm fan with a specs for 12V as:
    4200 RPM , 131 CFM , 45db

    When you volt mod it, everything should be lower by 7/12 ?? ( 76CFM, 27db, 2450 RPM )???
    Is it how it work ?

    If the fan has 3 pin , how could I change to 7V and where do I plug into ? Do I plug into the regular 12V power molex from the power supply ?

    Many thanks

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