Fan RPM readings??

OVI · Post by **OVI** » Tue Feb 15, 2005 1:56 am

Im confused. I just replaced my CPU fan with a Yate Loon d80sh-12 80mm which i took from an cheap Component Pro 300w PSU.

This fan had only two wires (red&black) but when i plugged it into my MB cpu fan header I noticed that I can see its RPM in Hardware sensors monitor. I was under the impression that in order to see RPM readings I should have fan with three wires??

The reading which Im watching right now changes slightly every now and then just like before when I had a fan with an RPM lead. And also when i adjust the asus Qfan (fan control)utility in BIOS the reading changes.
I can also see the RPM reading in BIOS and it seems correct when compared to the fan specs I found on Yate Loon website.

Please tell me whats going on, is my comp making up these readings or what??

Tibors · Post by **Tibors** » Tue Feb 15, 2005 2:13 am

Without that third wire it is absolutely impossible for your computer to know the RPM that fan runs on. So that number is comming from another fan or Qfan has gone insane.

OVI · Post by **OVI** » Tue Feb 15, 2005 2:44 am

Thank You for your swift reply. Thats what I thought, so my comp is insane

Mr_Smartepants · Post by **Mr_Smartepants** » Tue Feb 15, 2005 2:50 am

Tibors wrote:Without that third wire it is absolutely impossible for your computer to know the RPM that fan runs on.

Well, that's not entirely true. 'Fancontrol' posted somewhere around here that he built (and sold) a fan RPM sensor unit to supply accurate RPM data to motherboards for two-wire panaflo fans (and other two-wire fans). His device senses the feedback pulses on the DC+ line and supplies an amplified signal (conditioned) to the third pin for RPM sensing. I can't remember the thread but just search for the author 'fancontrol' and you should be able to find it.
(edit) Here it is: http://forums.silentpcreview.com/viewto ... highlight=

It's POSSIBLE that Asus came up with their own solution for this and incorporated it into their motherboard design for Qfan usage.

Although it's more probable that another fan is being read and the BIOS is reporting incorrectly. To eliminate this possibility, unplug all your fans except the two-wire one and see if it still reads the RPM.

Any other Asus Qfan users want to chime in?

frankgehry · Post by **frankgehry** » Tue Feb 15, 2005 3:43 am

I have an asus board with qfan and if it were able to sense rpm with only two wires I wonder why it needs the rpm wire from the power supply to get fan speeds. - FG

EDIT: Probably because the psu fans are not connected to the mb except by the speed wire.

OVI · Post by **OVI** » Tue Feb 15, 2005 6:43 am

Ive got only two fans connected to the MB. PSU and CPU fans and I get readings from both of these. I quess i could try another two-wire fan tomorrow. Ive got an 1500RPM PAPST 8412NGL lying around and if I still see readings which look like correct I'll report back here.