SP120 PWM fans at full speed. Need help!

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bslate

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Dec 29, 2013
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I am running 2 SP120 performance edition PWM fans on my CPU rad and they are connected to a Swiftech SATA 8-way PWM fan splitter. The motherboard is a EVGA P55 Classified 200 and the BIOS is configured with SmartFan enabled.

When I plug only one fan directly into the CPU fan header or via the powered splitter, the fan is speed regulated as set in the BIOS. As soon as I plug the second fan into the splitter, both fans immediately ramp up to full speed.

I can't figure out what is happening to lose the speed regulation when both fans are plugged in. Any help would be greatly appreciated!
 
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Krishna Moorthy

Krishna Moorthy

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Dec 27, 2013
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Are you using a normal splitter or a pwm compatible splitter because i think this is your issue. The PWM signall will not be sent over normal splitters.
 
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bslate

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Dec 29, 2013
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I'm using this Swiftech PWM splitter.

http://www.swiftech.com/8-waypwmsplitter-sata.aspx

 
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bslate

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Dec 29, 2013
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You mean the 4 pin connector that goes from the splitter to the CPU fan header? If so, yes it's plugged in. With only one fan plugged into the splitter, it is regulated by the BIOS settings and is reading the RPMs properly, but when I plug the 2nd fan in, both fans go to full RPM. The RPM reading is correct at 2180ish but the BIOS is still trying to run the fans at 9% based on current temp.
 
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bslate

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Dec 29, 2013
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I don't see anything about having to plug into a specific port but I tried connecting the second fan to several different ports with the same result. I'm wondering if the problem is with the fans rather than with the splitter or motherboard.
 
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ameel

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May 30, 2014
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Hi guys, had ad similar issue running a pump and 6x SP120s on the 8-way splitter. Do not despair!

I built a PWM amplifier by following the schematic posted by bing on overclockers.com, here:

Schematic from bing posted here: http://www.overclockers.com/forums/showthread.php?t=700653

Parts needed:
556 Timer
4k7 resistor
100 upf capacitor

I've also hotglued the bottom of my board to avoid any risk of shorting.

My pc is now DEAD QUIET!!! (awesome SP120s)

Here are some pics:
Top
fayhle.jpg


Bottom (pre-hotglue)
2ajbqu.jpg


Bottom (post-hotglue)
fn740x.jpg


All Connected
2pzw3gj.jpg


Original Schematic (by bing)
28qvn6h.jpg


No-clutter design
o53rpt.jpg
 
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arhshine

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Nov 5, 2014
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Isn't there any other solution than building this PWM amplifier ? I have the same problem, when i plug the second cooler in the splitter, both coolers ramp up to full throttle. Both coolers are from the Cooler Master 280L watercooler package, 4 pin each and the splitter is from the same package as well.
 
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