Need help with fan splitting

[Rozerum]

Hello,

I have an Asus P8P67 Pro Rev 3.1 mobo, which has 4 fan headers, two are 4 pin (CPU and CHA1), and the other two are 3 pin (CHA2 and PWR). My case is an Antec Nine Hundred, which currently has 3 case fans, two in the front and one in the back (as factory installed).

My goal was to switch out the fans for PWM ones, and I got 3 Xigmatek XLF-F1255 for free after rebate, but now I'm stuck with how to configure them. I read all over the forums and found that in order to connect two fans to a header, I just need to make sure they won't overload that port. Now the fans are rated at 0.2A each, but the motherboard manual only specifies a maximum of 1A for the CPU fan, with no mention of power ratings of the remaining headers.

Should I get two 4 pin splitters, and run all 3 case fans off the single CHA_FAN1 header, hoping it can supply at least an Amp? Or should I put two on that header, and the remaining one splitting the CPU header with the CPU fan?

Semi side note, I've also gathered that when splitting two fans on a PWM header, the tach result will show the combined speed of both fans in the BIOS. Will this affect how they function ie. slowing both fans thinking they're running too fast? Or will they operate normally, just showing an erroneous RPM reading on the BIOS display?

I appreciate any assistance you can provide, thanks.

Edited to add links, now that I'm not posting from my phone.

 

[Rozerum]

Can anybody provide any input please?

 

[janas19]

Can anybody provide any input please?

Hmmm. I'm no expert, but what I gathered on Google is this: the 4 pins on the fan header are +12v, ground, sense, and control. 3 pin headers have only the first three and run at 100% speed all the time. The four pin headers have the control line, which allows the fan to be pulsed on/off variably.

If you run more than one fan per header via a splitter, all four lines will operate on all connected fans. That means the control will pulse all fans which is good, but it will also add the RPMs together, which you don't want.

So according to an archived thread I read, what you want is the control, +12v, and ground running to all fans, but the sense running to only one fan on the splitter.

The way they set it up was to cut the sense wire on the extra fans. Hopefully, your motherboard manual specifies which pin is which, so it will be easy to do.

That was all I could find

 

[natto fire]

Hmmm. I'm no expert, but what I gathered on Google is this: the 4 pins on the fan header are +12v, ground, sense, and control. 3 pin headers have only the first three and run at 100% speed all the time. The four pin headers have the control line, which allows the fan to be pulsed on/off variably.

If you run more than one fan per header via a splitter, all four lines will operate on all connected fans. That means the control will pulse all fans which is good, but it will also add the RPMs together, which you don't want.

So according to an archived thread I read, what you want is the control, +12v, and ground running to all fans, but the sense running to only one fan on the splitter.

The way they set it up was to cut the sense wire on the extra fans. Hopefully, your motherboard manual specifies which pin is which, so it will be easy to do.

That was all I could find

Pretty much this. As to your original question OP, if the case fans are the same, I would do as you say and double split the chassis fan header. Snip one of the sense wires on each splitter. (I have seen it many different colors, usually blue, though). Make sure you daisy chain the splitters with the plug that still has the sense wire. Then connect your 3 fans, and hope they don't actually draw more than an amp. I know my Panaflos draw 1.2 amps EACH but the fans that came with my LL Armorsuit claim .27 amps. I have measured fans drawing more amperage than is claimed on their labels.

 

[coffeejunkee]

If the information in the manual is correct the cha_fan1 header isn't actually pwm controlled. Compare cpu_fan to cha_fan pin layout, and you see cpu_fan has a pwm pin whereas cha_fan has a 5V pin.

This is in line with the fact the 2 cha_fan headers don't offer individual control. The same voltage regulating circuit controls both fan headers at the same time.

So you don't really need pwm fans but you should still be able to control them just fine by voltage. I'm not sure what parameters the bios uses to decide fanspeed (rpm readout, which indeed gets messed up by a splitter, or percentage) but you could always use Speedfan to control fans.

 

[Zardnok]

My recommendation is to pick up a Sunbeam Rheosmart fan controller if PWM control is what you are after. It will not allow you to use the PWM function of the new fans you have, but the Rheosmart itself can use PWM to control the speeds of all of your fans or you can over-ride the PWM support and manually adjust the fan speed. Each fan channel can handle 30 watts, or 2.5A, and has decent heatsinks on the outputs.

 

[coffeejunkee]

Sounds interesting, but if the cha_fan is indeed not a pwm header you would have to use the cpu header to transmit the pwm signal. This might not be suited for the casefans. Or at least you give up individual control.

It's also 30$ to solve a problem that is not really a problem. Just use 1 splitter to connect 2 fans to cha_fan 1, connect the 3rd fan to cha_fan 2 and control voltage either from bios or Speedfan.

 

[Rozerum]

Thank you for all the info. Especially Coffeejunkee, I hadn't realized the two 4 pin headers were not the same. Basically, the fans that come installed in the case have a Lo/Md/Hi "switch" attached to them, and I just wanted some that could be automatically controlled based on temp. I thought that could be done with PWM fans because I misinterpreted the 5v fan header (which as i'm gathering is for controlling fan speed through voltage?).

I would just use the original fans (I honestly liked them better) connected to the headers, but they ONLY have Molex connecters, rather than typical fan connecters. So they can't be connected to the headers in the first place

But if i'm interpreting this correctly, the CHA_FAN1 header reads how fast the fan is spinning, and uses that to control CHA_FAN1, CHA_FAN2, and PWR_FAN all with that data from the one header? Or does it just control the first fan, with the remaining two spinning at full speed all the time?

 

[coffeejunkee]

Right, the (in)famous Antec tri-cool fans...

I'm not sure what the 5V pin does, it might actually do nothing at all. Apart from that cha_fan 1 is just a regular 3-pin header: cha fan in reads rpm, cha fan pwr provides 12V power and GND for ground. Same as cha_fan2, although for some reason they use different terms to describe the pins. So these headers don't provide pwm control but they do provide voltage control, albeit not individually.

The pwr header is not controllable at all. It's actually meant for reading out the psu's fan rpm, but not many psu's offer this feature.

So what I would do to use your new fans is buy a 4-pin splitter and connect 2 fans to cha_fan 1. Then connect the 3rd fan to cha_fan2, which should fit even though it's a 3-pin header. Then control them by voltage instead of pwm signal. I think bios fancontrol will work but if not, use Speedfan (you might need to google how to properly configure it).