Reversing Fan Headers to slow the fan down ?

[conan]

Posted this in three forums now but can't seem to get an answer, hoping the clever guys here can help

If I reverse a 3 pin fan header it slows the fan down, thing is I don't know why. Can anybody tell me whats going on and more importantly if it wil cause any damage to my mobo long term?

Effectively what I'm doing is connecting the ground pin to the rpm monitor/control pin. What I don't know is how it works

[Stoo]

because you're changing the voltage down to 7 volts
aka "7 volt mod" , look it up in google

I think..

[streetster]

thing is.. it isnt 7v them cos there are 3 pins:
1. 12v,
2. earth
3. fan speed header... so connecting the other way is just a bit sketchy really, and i wouldnt recommend doing it

mark

[conan]

so connecting the other way is just a bit sketchy really, and i wouldnt recommend doing it

I realise its sketchy, I'm trying to find the detail out. If its safe to do it's a very nice quiet mod

[megah0]

use a molex and connect the red wire to the black wire next to the yellow wire (if that makes sense).

so it goes: Yellow, Red, Black Black instead of Yellow, black black red.

[bmh.01]

If you want to slow fans down on 3 pin motherboard headers then you can use Speedfan :

http://www.almico.com/speedfan.php

[SilentDeath]

Posted this in three forums now but can't seem to get an answer, hoping the clever guys here can help

If I reverse a 3 pin fan header it slows the fan down, thing is I don't know why. Can anybody tell me whats going on and more importantly if it wil cause any damage to my mobo long term?

Effectively what I'm doing is connecting the ground pin to the rpm monitor/control pin. What I don't know is how it works

thats not a good idea!
i assume your connecting it as so:
1. fan + <--> +12v
2. earth <--> Nothing
3. fan speed header... <--> Ground

the speed pin, iirc gets a pulse either once or twice every rotation of the fan - this is what the mobo counts to give an rpm reading. all your doing is shorting out the IC inside which could possibly damage the fan. assumiong the pulse is 12v, assuming the only conenction to the mobo is then ground -> speed pin on fan, and 12v <-> fan+, then it cant cuase any damage to mobo.
it works sortof similarly to pulse width modulation - your still giving the fan full voltage, but not ALL the time. if a capacitor was added somewhere, it would smooth the DC power out to a constant voltage between 0-12v. your fan almost may have trouble starting...

[conan]

Didn't want to do it with a molex as I was trying to keep the wiring to a minimum. Done it using a Zalman adaptor I had now.