• Welcome to Overclockers Forums! Join us to reply in threads, receive reduced ads, and to customize your site experience!

Guide to the 7v Fan Mod

Overclockers is supported by our readers. When you click a link to make a purchase, we may earn a commission. Learn More.

doom0

Registered
Joined
Oct 23, 2006
i have one inside my case as an intake @12v. and its near silent.
i want to see it perform @24v tho.
 

Oc1Kenube

Member
Joined
Mar 5, 2007
Just used this on a delta screamer 80mm fan that was ear pericingly loud,it is still audible now but bearable.

Many thanks
 

jimmsch

Member
Joined
Nov 20, 2006
Location
NY
I have these pics of the different voltage wirings printed and tacked to the wall in my garage where I do all my PC building/testing/money wasting stuff. Great guide!!
 

Oc1Kenube

Member
Joined
Mar 5, 2007
jimmsch said:
I have these pics of the different voltage wirings printed and tacked to the wall in my garage where I do all my PC building/testing/money wasting stuff. Great guide!!

Could you post me a 5v mod please delta is still a tad too loud
 

nd4spdbh2

Member
Joined
Nov 15, 2005
Location
Camarillo, CA!
Oc1Kenube said:
Could you post me a 5v mod please delta is still a tad too loud


its very simple... take the 5v (red) line off the psu and put it to the + on the fan, then the - on the fan to a black or ground on the psu.
 

Oc1Kenube

Member
Joined
Mar 5, 2007
nd4spdbh2 said:
its very simple... take the 5v (red) line off the psu and put it to the + on the fan, then the - on the fan to a black or ground on the psu.

Confused. im using a pass through molex to molex mod like shown in the picture on page 1
 

SkuToV

Member
Joined
Dec 25, 2007
Location
Drunken Stupor, UK
What I did to mod the voltage on my 120mm fan on my case was I cut the plug so it fitted onto the molex the other way round so it's now running off 5v. works just as well as whats described above but its a helluvalot simpler
 

bardos

Member
Joined
Sep 2, 2002
Location
Haiku, Maui
question: i'm using a 120mm fan that at 12v is rated at 69 cfm and 36dba. I've tested it at 7volts and it is of course noticeably slower and quieter. is there some formula to let me know what cfm i could expect at this voltage (and dba)?
 

Foolios

Member
Joined
May 9, 2006
How is it that you can have one wire going to +12v and one wire to +5V and get 7v? Why do these take away instead of adding up?
And how is it that when you switch the black ground wire away from the ground and into the 5v that this works at all now that the ground is no longer there?
It would seem to me that the two voltages would buck and burn things out if this was to work at all. This is DC so I would think that since everything is going one way that it wouldnt work.

What gives?
 

eobard

Give me a break Senior
Joined
Jul 12, 2001
How is it that you can have one wire going to +12v and one wire to +5V and get 7v? Why do these take away instead of adding up?
And how is it that when you switch the black ground wire away from the ground and into the 5v that this works at all now that the ground is no longer there?
It would seem to me that the two voltages would buck and burn things out if this was to work at all. This is DC so I would think that since everything is going one way that it wouldnt work.

What gives?
It's not going one way. The 12v is pushing in one "direction" if you will, and the 5v is pushing in the opposite direction. So the first 5v of the 12v line are canceled out leaving only 7v remaining. Now that is in no way what I would consider an accurate technical explanation, but it does make the point in an easy to understand manner.
 

Foolios

Member
Joined
May 9, 2006
Thank you for trying to explain it.

But where is the ground? I don't understand how this completes the circuit without a ground.
I am wondering how it is possible to use a wire to output voltage and current and yet still perform the job of a return.

Very interesting stuff!
 

MattNo5ss

5up3r m0d3r4t0r
Joined
Aug 11, 2008
Thank you for trying to explain it.

But where is the ground? I don't understand how this completes the circuit without a ground.
I am wondering how it is possible to use a wire to output voltage and current and yet still perform the job of a return.

Very interesting stuff!

The 5v wire is the "ground" with the left over 7v running through it to complete the circuit.

I used the 3.3v wire as a "ground" to mod my Panaflo to run at 8.7v (12v-3.3v=8.7v).
 

noxqzs

Member
Joined
Feb 21, 2005
Location
Boston, MA
When you think of voltage, you must think in terms of difference in potential energy. Voltage is a difference between two points. A simple example could be a ball at the top of a hill. The higher up on the hill, the bigger its potential energy. If you took 4 3v LEDs and wired them in series powered by a 12v source. The measured voltage between each led would be 3v.
 

Foolios

Member
Joined
May 9, 2006
Saying that there is difference in potential makes sense in a way to me. There are two wires to complete a circuit.

But the part I can not get around is that this method does not appear to include a positive and negative side.

I can almost imagine this working with a/c because I know that current can travel in two directions with a/c. But in a/c I don't believe this would be the case as if one were to do this with a/c, I believe the two voltages would buck.

But in d/c don't we need the difference to be between a positive and negative, the negative supplying the electrons(current) to the positive side?
I am imagining a circuit that is being created with this mod having two positive sides and no negative.

Ooooohhhh, wait a minute.. You are saying that because one side is lower in voltage than the other that it will give up electrons to a higher voltage source? So, a positive with only 5v will now act as a negative and give up electrons to the side with 12v? The 12v has a stronger attraction and wins over?

Whoaaaa!!!!!!!!
 

Foolios

Member
Joined
May 9, 2006
EDIT:
Works with 3 fans at 7v on the same cable.


What about cables that have other devices like hdd's on them, can this mod be used on those just at the point of the fan connection or will it cause power problems along the rest of the cable?
 
Last edited:

Foolios

Member
Joined
May 9, 2006
this is an easy way to do it yes, but if somone has a bit of knowledge in electronics you can easily set up a NE555 timer as a PWM modulator with a transistor and controll your fan speeds very acurately. If anyone is interested let me know and ill post the information. PWM (pulse width modulation) is very acurate and can run a fans speed slower than a voltage modification, because the PWM controller runs the fan at its desired voltage the fan will start at very low speeds.

I would love to see this.