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Low rpm on chassis fan 3

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July 20, 2010 12:57:26 AM

Greetings,

While running pc probe II, I keep getting warning messages about low rpm on chassis fan 3. Chassis fan 2 runs at about 1100 rpm's while fan 3 is around 700. Fan 3 will drop to the 400-500 range for a couple of seconds at a frequency of about once every 5 minutes, which trips the alarm.

I think the drops are due to the fact I am running a splitter to 2 case fans since I couldn't find a 4 pin to 3 pin connector to connect to chassis fan port 1. I am assuming chassis fan 3 is not getting enough power since I am running 2 fans with it. Is there any way to increase the power to port 3 or would it be easier to just find a 4 to 3 connector and connect a case fan to port 1?

My Computer
Asus P6X58D Premium
i7-920
Thermalright 120
Corsair 850 hx
XFX 5870
Corsair dominator 3x2 gb
WD caviar black
Silverstone FT-01 case

Thanks for any suggestions!

Update: I'm an idiot. It looks like I can just plug the 3 pin fan plug into the 4 pin port on the motherboard.
http://www.intel.com/support/motherboards/desktop/sb/im...

More about : low rpm chassis fan

a b B Homebuilt system
July 20, 2010 2:25:36 AM

Not an idiot! A student, with the world as your classroom.
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a b B Homebuilt system
July 20, 2010 3:23:35 PM

Yep, you fond the 3-pin to 4-pin solution: it works that way.

Now, I'm a little intrigued with your statement about using a "splitter" to power your fans. Do you mean you have some adapter you purchased that allows you to plug two 3-pin case fans together into one 3-pin mobo SYS_FAN3 pinout? And, that is the fan that reports low fan speed, right? (Well, if I understand correctly, it's really 2 fans on one output.) Check something for us. I have seen entirely too many adapters for this that simply connect in parallel all three leads for two 3-pin fans. That is, they bring 2 black leads together to one connector, and two reds together, and 2 yellows together. The two YELLOWS together is a problem! And I really do not understand why they make these adapters like this. Each yellow wire takes a pulse signal generated by its respective fan motor (2 pulses per revolution) back to the mobo to measure fan speed. By connecting two yellows together you end up feeding the pulse signals from two sources together, so they overlap giving twice as many pulses to the mobo. Even worse, the fans will NOT run at exactly the same speed, so the relative timings of the pulses will change constantly, causing no end of confusion for the measuring/timing circuit! What you should do is allow only ONE of those yellow wires to connect back to the mobo. That fan's speed will be measured and displayed for you. The second fan with NO yellow lead connected back will never have its speed measured or known, and that's OK. You just need to check occasionally that it is still working. As long as its red (+ 12 VDC but varying for speed) and black leads (Ground) are connected with the other fan's, they both will operate under speed control from the mobo.
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July 27, 2010 3:26:02 PM

Haha, thanks for the words of encouragement treefrog07 :D 

Paperdoc - yes, all three wires merge together into the plug. Here, I even found a link to the one I bought:
http://www.frys.com/product/4586767?site=sr:SEARCH:MAIN...

On a good note, now that I pluged in the case fans into separate ports, my computer is running 5C cooler!
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a b B Homebuilt system
July 27, 2010 3:34:31 PM

Yep, that's what I would call an "offender" type of 3-pin 2-for-1 fan splitter. I would simply snip one one of the two yellow leads and tape it safely out of the way.
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