Building my new rig : why undervolt? Seems dumb.

[Habeed]

Well, maybe not dumb, but "sub-optimal". Got you to click

Motherboard : ASUS Sabertooth X58. Case is a Haf X. CPU is i7 930 at 4100 mhz. All power saving options are still enabled at this overclock. So it runs very cool at idle (33 C) and crazy hot during an OCCT stress test (85-90 C on the hottest core). It needs barely any air to cool it during normal use but needs a tornado when it's benchmarking time.

Using 4 wire PWM splitters, I ghetto rigged it so that all of the case's fans share the motherboard's 4 temperature controlled fan headers. 2 fans per header, I ripped out the yellow "fan RPM" wire for the second fan on each header. For those who have this specific board : the headers are

CPU_FAN ( for some weird reason, this one will NOT voltage regulate. It will ONLY do PWM regulation)

CHA_FAN1
CHA_FAN2
CHA_FAN3

In the BIOS or in a software utility from ASUS you can set the fan's regulation. For the CPU_FAN, you can specify a custom fan curve.

For the CHA_FAN headers, you can make it do 60% voltage (probably 7.2 volts) and smoothly ramp up when CPU temperature exceeds a certain point. I found that SpeedFan can also talk to the fan controller chip and do any % speed, which presumably means any voltage from 0 volts to 12 volts. The fans will stop spinning at all around 30%. I think SpeedFan can do custom fan speed curves but I couldn't figure out the interface or find any options for this.

So why undervolt with a fixed voltage when you can have the motherboard set any voltage you want and increase it when you need more cooling? Seems like it would be simpler to just buy a slower fan if you want to be at the same speed always. I just hate the idea of not making my hardware able to 'defend itself' from getting too hot. What if I put the machine in a hot room and want it to keep working?

My questions :

At the moment, one fan is unregulated. It's one of the cpu fans, which is the 140mm Noctua that comes with the DH-14 CPU cooler. Noctua fans do not support PWM. So I just purchased this one : Scythe Kama Flex 120mm PWM Fan. Is this fan any good? I found that similar fans scored highly on this site, but not this exact model.

As an experiment I unplugged this fan while the machine was running (there's another fan on the DH-14 that is running on a chassis header) and it was sweet, blessed near-silence. THAT's what you folks enjoy all the time. Wow. Course, I could still hear my Western Digital black making annoying clicks and could hear all sorts of little noises that are normally drowned out...

How the heck do you make SpeedFan regulate your fans automatically according to temperature?

And one final question : My case has a fan duct aimed at the front of my video card(s). It has a spot for a 120mm fan. I'd like to make this particular fan regulated by the temperature of my video card(s) rather than by cpu temp. The motherboard regulates all the case and cpu fans by cpu temp, which is normally fine - I know the northbridge and RAM get hotter only when the CPU is under heavy load. But some games only really stress my gpu, while my cpu just loafs along.

So I looked at the video card. It has a connector for a fan that looks like this : (photo courtesy of newegg)


And this guy on ebay is selling this : http://cgi.ebay.com/PCI-E-Express-Cooli ... 740wt_1258

Basically I'd use a PWM fan and have that green wire sharing the PWM signal with my 120mm fan as well. Does anyone have an easy way to wire this up that doesn't require soldering?

[Habeed]

Found a solder-less solution. 2 bucks on ebay will score me some "T-tap" connectors.
http://cgi.ebay.com/14-16-Gauge-Quick-S ... 700wt_1604

Evidently this is a little plastic thing you can use to quickly connect 2 wires together. So I can just put the green wire from a PWM 120mm fan next to that green wire on my video card and CLICK instant connection. Plug the fan into a motherboard header (so I can see the speed of the fan in software) and I think the PWM fan will run at the same relative speed to the fan on my video card. Also would work with multiple video cards, just make the primary card the one that I splice into. The damage from this kind of slice is probably slight enough that if the card were to fail for an unrelated reason before the end of it's life I could probably RMA it without any questions asked.

But this brings up anther problem : which wire's which? Is that green wire really for the PWM signal or is that signal from another wire? Does anyone know anything about the pin outs for that connector?

[ntavlas]

From left to right: pwm signal (blue), rpm signal (green), +12volts, ground. If you removed the white plastic bit from the fan header you could possibly plug in your pwm fan with no further modification. The spacing between the header's pins does not exactly match, but it should be doable.

[b_rubenstein]

Those T connectors, AKA Scotch Locks, are for 14 - 16 gauge wire and would not displace the insulation for those fan wires. The red version for smaller gauge wire might work, but they are about 3x bigger than the connector on the end of the wire.

[wouterr5]

For controlling fan speeds with temperature, using speedfan:
http://unitstep.net/blog/2007/11/02/usi ... an-speeds/

From what i've found out getting a Arctic Cooling Freezer 7 fan to work on a 4870 and a 9600 GT, the pinout of the little fan connector is the same as on the big CPU-fan connectors.
So starting at the black wire, you have ground, 12volt, RPM sense, and PWM control. PWM on fans is really neat - if you want it to be as silent as possible, you can even use a paperclip to make a connection between the ground and PWM wire - which will give 0% duty cycle, making the fan run at it's minimum speed.

The concept of using the CPU PWM value for in- and outtake, although extremely sensible, isn't much used on SPCR it seems, because of the need for PWM fans and cable splitters. When you've finished, tell us if it really works as good as expected

[KayDat]

You can try getting this PWM fan controller. Its supposed to convert four pin PWM fan to three pin. I've had trouble getting it to work with my 5870 though, I think it may have to do with how AMD implemented their fan PWM signalling though. Nvidia cards may be okay though. There are a couple of other products out there that convert PWM fan signals for regular voltage controlled fans, such as the Nanoxia PWMX, and the PAQT PWM->DC converter.

[Habeed]

Thanks for the suggestions. I'll pick up the red T-types and a PWM fan.

[crispy]

If you want to use a the CPU headers I would just use a pair of Akasa Viper Pwm fans (for a push pull rig for example).

You can use one of these cables:
http://www.scan.co.uk/products/akasa-ak ... n-pwm-fan-(plus1-connectoer-for-rpm-feedback-for-the-motherboard

Powers the fan from powersupply and gives the pwm 5 volt line to each fan from CPU_FAN header.

For others come across this post looking to get fan control over there sabertooth let me give a little more info.

Available fan headers on the asus sabertooth x58 are:

CPU_FAN PWR_FAN CHA_FAN1 CHA_FAN2 CHA_FAN3 NB_FAN

First asus Fan expert sucks. I would recommend speedfan which is very easy to use just use the help.
If you use speedfan you will see it finds 3 Speed controls (not in the following order).

One: Controls the CPU_FAN header which PWM 4pin only (no undervolting).
Two: Controls CHA_FAN 1,2,3 (all linked) Intake Front/Bottom,Exhaust Rear
Three: Controls NB_FAN header

PWR_FAN is the only header without control and stays constant.

The main point of me saying this is that you don't need to have PWM fans on the cpu you DO have two dc voltage control headers even if the asus software won't control them.
You can use regular fans with a simple splitter going to the NB_FAN header which is not far from the CPU in the middle of the board.

If you are using very highspeed fans remember that each fan header only supports 2amps so check the rating if you are using splitters.

Hope this helps someone else before you have to reorder fans and cables.