another way to undervolt a fan

jcuesico · Post by **jcuesico** » Tue Apr 22, 2008 2:17 pm

I've seen the 7V trick by putting the fan between the +12V and +5V line.
Some people have concern if this will damage the PS since there is current flowing into the +5V of the PS.

I am wondering if anyone else has tried what I've done to undervolt a fan with tach/speed sensor.

I connect the +12V to the red wire, same as before. But now, instead of connecting the GND of the PS to the GND of the fan, I connect the GND of the PS to the tach/speed sensor. I leave the GND of the fan unconnected.

The fan will work, but now it will be a lot quieter. I measured the voltage between the +12V and GND of the FAN. I get approximately 6.5V.

So it's as if the fan was connected to 6.5V instead of 12V.

Has anyone else tried this?

cpemma · Post by **cpemma** » Wed Apr 23, 2008 2:38 pm

jcuesico wrote:Has anyone else tried this?

No, and I'm not going to.

Post by **NeilBlanchard** » Wed Apr 23, 2008 3:05 pm

Hello,

jcuesico wrote:I've seen the 7V trick by putting the fan between the +12V and +5V line.
Some people have concern if this will damage the PS since there is current flowing into the +5V of the PS.

In theory, this could be problematic -- but in practice, there are no problems that I have heard of.

You can also run a fan from the 5v line. You can plug it into a motherboard header and control it in the BIOS. You can buy a Zalman FanMate 2 (about $5) and get ~5-11.5v. And you can buy a fancier fan controller. You can put a resistor or diode(s) on the 12v line.

another way to undervolt a fan

another way to undervolt a fan

Re: another way to undervolt a fan

Re: another way to undervolt a fan