How to hook up a replacement PWM fan to PSU?

Islander · Post by **Islander** » Thu Oct 02, 2008 6:54 pm

Hello all, been reading here for a while trying to learn about things in advance of building my first HTPC. Unfortunately I had bought some parts prior to fnding this site. My biggest mistake (well, one of them) is that I bought a noisy PSU, or think it would be, have not assembled my PC yet, just got the box of parts this week. The first thing I have done is to replace the cheap exisiting 2 pin fan that came with the CoolerMaster PSU with a Nexus 120mm RS PWM type, and have the wires coming to the outside of the unit. (yes, I know, voids the warranty but don't care) Currently working in Japan, but will be using the PC in Phuket where I live and it will be for general use as well as HTPC. You can see my system details below.

My question is, where should I connect the PSU's Nexus PWM replacement fan to? There is no PSU fan header on the MB, and the 2 pin in the PSU is useless, I think, as far as taking advantage of the PWM fan. I want the fan to run slow and quiet during low power consumption (which will be most of the time, I'm not a gamer) and faster during high power usage. What is the best solution? (Other than buying an Enermax Modu or similar which does what I want without having to go through this

Thanks in advance for your help, great to have a place like this to help us noobs!

System:
Case: Silverstone LC20S-M
MB: Asus P5E3 Deluxe
PSU: Cooler Master RS700 w/Nexus RS PWM replacement fan
Boot Drive: WD VelociRaptor 300GB
Storage: Samsung Spinpoint F1 1TB
CPU: Intel Core 2 Quad Q6700
RAM: Corsair 4096MB PC12800 DDR3 1600MHz
DVD: LG Electronics GGW-H20L
GPU: Diamond Radeon HD 3850 Video Card
CPU Cooler: Thermalright SI-128 SE w/Noctua NF-P12 fan

lodestar · Post by **lodestar** » Fri Oct 03, 2008 4:48 am

The solution might be the CoolerMaster Wind Rider PWM Fan Hub, which sells here in the UK for Â£11, so not too expensive. You plug both the CPU and PSU PWM fans into the Wind Rider, which takes its power from a conventional 4 pin molex. The Wind Rider also connects to the CPU fan PWM header.

Both the CPU and PSU fans will then be controlled by the voltage at the CPU fan PWM header i.e. when the PC is heavily loaded both fans will run faster, and when the PC fan is idling they will run more slowly.

The Wind Rider enables you to set the level at which the fans operate, so you can opt for quiet at the expense of higher temperatures if you wish.

See
http://www.coolermaster.com/products/pr ... il&id=2521

Islander · Post by **Islander** » Fri Oct 03, 2008 10:16 pm

Hi lodestar, thanks for the idea. I had seen in another thread here at SPCR forums where somebody had suggested something similar, that is just plugging the PSU fan directly to the CPU fan header, but my concern (not very sure about this stuff!) would be: What is the correlation between CPU usage and PSU power output? Is it always directly proportional? If so, that would work as I could just run the Noctua CPU fan with the LN adapter plugged in elsewhere. But I was wondering about things like, watching a Blueray DVD, with the GPU running it... wouldn't that make the power supply jump without much CPU usage? Maybe I worry too much, but would like to get it right

Also, am a bit reluctant to buy anything else from CoolerMaster. Not much info on their website, or in their manual, but did find a FAQ where they said they removed the fan speed control logic system because it "was too confusing" for thier customers, sounded a bit lame, and then in their PSU manual they say the fan should be controlled for speed, but don't say how.

maf718 · Post by **maf718** » Sat Oct 04, 2008 6:11 am

Islander wrote: and then in their PSU manual they say the fan should be controlled for speed, but don't say how.

A two pin header/fan can control fan speed by varying the voltage the same as a three-pin fan, the only difference would be the lack of rpm monitoring that the third wire is for. I'm not saying that your PSU definately does this (I don't have one to check), but I would find it hard to believe that a modern 700W power supply from a big company doesn't have fan control built in.

If this is the case you could attach a regular three-pin fan to the two-pin header in the PSU, and let the PSU control it. That's what I would do in your situation, it seems less complicated than bodging something up to control a PWM fan.

Islander · Post by **Islander** » Sat Oct 04, 2008 6:53 am

maf718 wrote:
If this is the case you could attach a regular three-pin fan to the two-pin header in the PSU, and let the PSU control it. That's what I would do in your situation, it seems less complicated than bodging something up to control a PWM fan.

Thank you, I think that you are absoulyely correct.