Windows 7 Case fan voltage mod. Slow those noisy fans!

[kemical]

Let's say you've just fitted a new 120mm fan to the front of your pc. The wire isn't long enough to reach a motherboard fan header nor is there any way to modulate the fan speed. You've fitted it but it's going like the clappers and sounds way too loud... One answer would be to employ the fan voltage mod. (The original guide can be found here:
Guide to the 7v Fan Mod - Overclockers Forums )

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:
Link Removed

7v to the fans:


5v to the fans:


I've personally tried this and it works with the 7v mod being about right (5v was too slow). I would suggest though that this 'mod' only be employed where all else has failed.

 

[ChatGPT]

If you have installed a new 120mm fan in your PC and it's running too loud at full speed because the wire isn't long enough to reach the motherboard fan header, you can consider performing a fan voltage mod to reduce the fan speed and noise level. This mod involves powering the fan with lower voltage to slow it down. Here's a summary of the 7v Fan Mod based on the information from the overclockers.com guide:

• Fans in most computers are typically 12V DC fans, which can operate at lower voltages without issues. Some fans can even work well at voltages as low as 4V.
• To slow down a fan, you can power it off a different rail than the normal 12V rail. In addition to the commonly known +/-12V, +/-5V, and 3.3V rails, there are "virtual rails" like 8.7V, 7V, 17V, 24V, and 15.3V. These virtual rails are accessed by using a real voltage rail as a ground, creating the desired lower voltage.
• To achieve the 7V fan mod, you can use a 4-pin molex connector typically used for hard drives and DVD drives. By switching the fan's ground to a lower voltage rail (such as 12V + 5V), you effectively provide 7V to the fan, reducing its speed and noise.
• It's important to note that while this mod is relatively safe due to the overall load of the computer, it's recommended to check before attempting it. Also, using lower quality power supplies or attempting this mod without a load can potentially damage hardware.
• The 7V mod works well for many users as it strikes a balance between reducing noise and maintaining adequate cooling.

It's great that you have personally tried the 7V mod and found it to work effectively. This mod can be a suitable solution when traditional methods to control fan speed are unavailable or ineffective. If you have any specific questions or need assistance with implementing the 7V fan mod, feel free to ask!