Motherboard fan headers not controlling rpm and not showing up

So I have a gigabyte ex58-ud3r motherboard. It dawned on me I could clean up the inside of my case and quiet it down some when it's not being stressed. I removed all of the big clunky molex connectors and splitters and hooked my case fans 3 pin connectors directly to the motherboard system fan headers. No need to run full blast at idle I think. I have 2 front and one top 140mm fans (thermalright 900rpm) and one rear 120mm (also thermalright 900rpm) set up like so...

2 front 140mm fans - Hooked to a 3 pin y cable splitter and plugged into sys fan 1

1 top 140mm fan - plugged straight into sys fan 2 (4 pin input compatible with 3 pin fan with offset tab)

1 rear 120mm fan - Plugged straight into sys fan 3


The problem is the front 140mm's are running at full speed despite having a third wire for sensing rpm, and the rear fan along with sys fan 3 don't exist according to the bios and gigabyte easy tune. Despite not showing up in bios the rear fan is definitely on and spinning slower than it was before but I wish I could see the rpm. The only one working like it should (for sure) is the roof fan plugged into 3 of the 4 pins on sys fan 2. I used hwmonitor with prime95/furmark to make sure the speed was climbing with the heat. I also tried the top fan with sys fan 1 to make sure it was the header and it also ran only at full speed so it's not a certain fan or y cable. What am I doing wrong? I don't see anything else in the bios that would let me take more control of the system fans. Help please. Thanks!

1. You can't control fan rpm from the motherboard unless you have four wires. The third wire is the tach wire and just allows the reporting of RPM, not the controlling of it.
2. When you put fans on a splitter it can mess with the RPM reporting.

With a Gigabyte board you can control fans with Voltage, but only the cpu fan. And the current limit is one Amp, so be careful.

You tell your board to use Voltage by going into BIOS, choosing PC Health. Toward the bottom of PC Health there are a couple of options for Smart Fan. Enable Smart Fan. Auto is fine. Set control mode to Voltage. Do not set that to Auto.

Or get PWM fans. With a PWM splitter you can control many fans with a single fan header and not worry about the Amps.

I see what happened. I thought sys fan 2 was controlling rpm because the fan hooked up to it was at about 2/3rds speed and going up and down a little. I think it just runs at a lower voltage than the others. It seems to hover around 670rpm while the others are just over 900rpm. I still don't know why sys fan 3 isn't showing up in bios or easytune. Btw cpu smart control is set to pwm but has an option for voltage. Would it be possible to somehow control all fans with voltage control by using a splitter off the cpu fan header rpm sensor pin to every fan in the case and have them ramp up with the cpu temp? Or does the power for all fans have to come from the header itself? Sorry for my ignorance but I've always just used psu plugs my whole life. My cpu fans go up to 1600 rpm as opposed to 900rpm for the case fans to further complicate things. Last thing. Got a link to the right splitter that would make this work?

Blah. 140mm pwm fans are rare apparently and all the ones I'm finding are either the wrong speed or have 120mm mounting hole patterns. I think I need to start looking at fan controllers that can sense chipset temps and control 3 pin fans with voltage.

Brando said:

I see what happened. I thought sys fan 2 was controlling rpm because the fan hooked up to it was at about 2/3rds speed and going up and down a little. I think it just runs at a lower voltage than the others. It seems to hover around 670rpm while the others are just over 900rpm. I still don't know why sys fan 3 isn't showing up in bios or easytune. Btw cpu smart control is set to pwm but has an option for voltage. Would it be possible to somehow control all fans with voltage control by using a splitter off the cpu fan header rpm sensor pin to every fan in the case and have them ramp up with the cpu temp? Or does the power for all fans have to come from the header itself? Sorry for my ignorance but I've always just used psu plugs my whole life. My cpu fans go up to 1600 rpm as opposed to 900rpm for the case fans to further complicate things. Last thing. Got a link to the right splitter that would make this work?

Click to expand...

Smart Fan is set to pwm by default, I think. Setting it to Voltage will allow you to control up to 1 Amp of fannage.

The best Y-cables I have ever seen are these. Note the free shipping. They can handle hundred of fan changes. The one weakness is that the rpm reporting lines of both fans are intact. That means the motherboard may report erratic fan speeds unless you cut one of the yellow wires.

SYS_FAN2 will vary by Voltage or PWM, but based on the chipset temperature, not the CPU. That means, with modern chipsets, the fan never gets to full speed.

The best way to handle a batch of fans is to go PWM. That is what PWM was designed for: controlling a bunch of fans with a single fan header.

ehume said:

Smart Fan is set to pwm by default, I think. Setting it to Voltage will allow you to control up to 1 Amp of fannage.

The best Y-cables I have ever seen are these. Note the free shipping. They can handle hundred of fan changes. The one weakness is that the rpm reporting lines of both fans are intact. That means the motherboard may report erratic fan speeds unless you cut one of the yellow wires.

SYS_FAN2 will vary by Voltage or PWM, but based on the chipset temperature, not the CPU. That means, with modern chipsets, the fan never gets to full speed.

The best way to handle a batch of fans is to go PWM. That is what PWM was designed for: controlling a bunch of fans with a single fan header.

Click to expand...

That's how it's starting to look. I was hoping to avoid buying more fans since I JUST replaced all 4 case fans with the thermalrights for about 50 bucks. Also, I'm not seeing a lot of desirable 140mm pwm fans pop up on google. I'm considering the sunbeam rheosmart 6 or maybe the rheosmart 3 with some splitters but I'm getting mixed reviews and not sure how it handles multiple fans with different sizes and speeds. Hard to believe motherboard fan control isn't a standard feature these days. I honestly thought it was a given.

Oh and thanks for the link but I've been down the standard 4 pin y cable route with my cpu push pull set up. I ended up with this

http://www.newegg.com/Product/Product.aspx?Item=N82E16812718001

Took me awhile to find one with rpm sensing to only one fan and it works great on my 2 cpu fans but doing the whole case with mutiple speeds\brands\sizes seems to be a whole new can of worms.

ehume said:

With a Gigabyte board you can control fans with Voltage, but only the cpu fan . . .

Click to expand...

Didn't know that. Thanks for the info.

I can control all the fans with my board (in Bios) as soon as they have 3 wires: CPU, Chassis...

manu2b said:

I can control all the fans with my board (in Bios) as soon as they have 3 wires: CPU, Chassis...

Click to expand...

I guess my motherboard is just lame.

I tried putting a 1000 rpm fan on the pwr_fan header and it's showing 1200rpm. Weird.

Almost within the 10% reporting difference. They don't make these things to scientific standards.

Mobo easily coul;d be off 10%, 12 VDC could be off 10% to the mobo header, the reporting circuit could be off 10%.

Better than $500 for each part.

The PWR fan header is an uncontrolled 12v header. Consider it a bonus: some boards use it purely as an rpm input -- no power from the PWR header.

Not complaining. Just thought it was weird but yeah it's probably just reporting the wrong speed. I think I may be able to live with full speed fans but I definitely need to get rid of whatever this wmmmmwmmmmwmmm sound is. Something has to be loose in there. These aluminum cases can be a ***** to quiet down.

It looks like the sunbeam rheosmart 3 will do what I want. Apparently you run a sensor off a pwm splitter from the 4 pin cpu header to the fan controller and it senses the rpm of the cpu fan to determine how much voltage to send to the non pwm case fans. Not too expensive either. I think I can run the 2 front 140's off a splitter on one channel and the top\rear fans off their own channels. If somebody has this or the rheosmart6 and it sucks please stop me.

http://www.newegg.com/Product/Product.aspx?Item=N82E16811995074

Well, the thing works but my thermalright fans don't seem to handle under volting very well. I think the controller must be starting at 5v because on fan takes a couple minutes to come on as the cpu heats up and they all (thermalrights) make sort of a clacking noise like the sound of a locomotive coming from a couple miles out. It never ends (first world problems). Time to research low starting voltage fans that don't make annoying noises.