Can't get my 4 pin, PWM fans to work with a splitter

[d_wark]

I have 4 PWM fans but only one 4 pin connector on my MSI B150I motherboard. So I got this splitter to connect all the fans. http://www.newegg.ca/Product/Product.aspx?Item=N82E16812423166
When connected, all the fans run at 100% and there is no way to control them. I tried each fan individually and they all work perfectly when connected to the motherboard directly. I made sure that the one connector that actually sends the tach signal is plugged in to a fan. My power supply doesn't have a molex connection so i've used a molex to 6 pin adapter. Can't see that being a problem though. It's not the fans, so it must be a faulty splitter right? Or am I missing something?

 

[MauveCloud]

What psu do you have that doesn't have a molex connection? That seems very strange. Also, how could you use a molex to 6 pin adapter to connect that splitter? Those are to make it technically possible to power video cards from psus that have molex but not enough pci-e power connectors (though it's generally a bad idea to do so), so the plug genders would be wrong for hooking up a fan splitter like that.

 

[d_wark]

What psu do you have that doesn't have a molex connection? That seems very strange. Also, how could you use a molex to 6 pin adapter to connect that splitter? Those are to make it technically possible to power video cards from psus that have molex but not enough pci-e power connectors (though it's generally a bad idea to do so), so the plug genders would be wrong for hooking up a fan splitter like that.

Thanks for the response. Here is my power supply:
http://www.evga.com/Products/Product.aspx?pn=110-B2-0750-VR
I must apologize, the molex adapter cable that came with the power supply says it's a 4- pin peripheral cable. You'll have to excuse me as I'm not incredibly tech savvy so my language might be off sometimes...

 

[MauveCloud]

Ah, that's where the confusion came from. If it's a cable that came with the psu, then it's called a modular cable, not an adapter. EVGA B2 series are often recommended here for being good quality, so I agree that it's unlikely to be the problem.

I haven't used fan splitters much, but presuming you followed the instructions that came with the splitter and connected it to the motherboard header as well as the fans, the simplest explanation is that you got a defective splitter. Thus I suggest you try to send it back for a replacement.

 

[Dark Lord of Tech]

You will burn out the fan header running 4 fans on it.

 

[MauveCloud]

I could be wrong, since I haven't used that particular splitter myself, but I don't think the header is powering the fans, only providing the PWM signal and reading the RPM from one of them. That's why the splitter has a molex connector.

 

[Dark Lord of Tech]

Hopefully your right , because it will eventually render the header useless.

 

[Paperdoc]

SR-71 Blackbird has a point, but it MAY be open to debate. It used to be an accepted guideline that any mobo fan header could support up to two fans, but not more, without risking overloading it and possibly damaging that portion of the mobo. More recently the common fans' specs show them using 0.2 amps or less at full speed. CHECK the specs of your four fans. Now, almost all such mobo headers can provide a max of 1 amp to fans; moreover, some posts here have made a clear claim that mobo makers have said there is no need to de-rate that header spec for the momentary extra surge of current during start-up. That is, the 1 amp max applies to the steady-state running current, not the start-up surge. So as long as the total amperage consumed by all your fans is LESS than 1 amp, you should be OK.

However, you did not buy a SPLITTER. You bought a 4-PIN FAN HUB. There are two important differences. First is that a Hub has an extra arm that must plug into a power output connector directly from the PSU and this is what provides a constant 12 VDC supply for all the fans. The second is that the Hub's female fan connector plugs into the mobo 4-pin fan header and from it picks up the PWM signal to share to all the fans. At each fan, a small chip inside uses that PWM signal to modify the +12 VDC supply so that the motor speed is changed by the PWM signal.

The problem you have is that the only fan header on your mobo is NOT a 4-pin one using PWM Mode - see your manual, p. 15. It says the 4-pin SYS_FAN 1 header uses Voltage Control Mode on its first three pins, and the 4th pin is actually useless. Thus the Hub is NOT receiving any PWM signal to give to the fans, so they all are working on the fixed 12 VDC being supplied from the PSU. You post says that you did exactly what the Hub's instructions said and connected its Molex connector to a PSU output.

So what to do? Disconnect the Molex connector from the PSU output and leave it disconnected. When you do that the Hub will not receive any fixed 12 VDC supply. Instead its only voltage supply will be from the mobo SYS_FAN1 header's Pin #2, which is a VARYING DC voltage ranging from 5 to 12 VDC, and that is how a Voltage Control Mode header changes a fan speed. This is how all 3-pin fans work. But because of the design of 4-pin PWM fans, if the get NO PWM signal they will do whatever the voltage supplied on Pin #2 allows. Thus the 4-pin fans CAN be controled by the header you have IF you are using a true SPLITTER. And in your case, disconnecting the HUB you got from that 12 VDC supply via the Molex connector will make it behave just like a SPLITTER.

 

[MauveCloud]

@Paperdoc I hadn't noticed that issue with the motherboard, but if my suspicions are correct about the hub not being powered from the motherboard header, then with the molex disconnected, said hub won't even power one fan successfully.

 

[Paperdoc]

You may be right. Some of these Hubs connect the DC supply (Pin #2) of every fan output arm to BOTH the mobo's Pin #2 AND the Molex +12 VDC supply. When used with 3-pin fans and a 3-pin (Voltage Control Mode) mobo header, such Hubs do this: IF you connect to the PSU Molex then all fans will run at full speed constantly because the +12 VDC from the Molex is over-riding the variable voltage from the mobo header; BUT if you disconnect from the PSU and leave only the mobo connection in place, then the varying voltage on that single power source does control the fans' speeds.

HOWEVER, this particular Hub may not do that if it does NOT connect the mobo header Pin #2 (via the Hub's female fan connector) to the output arms. No detail about that is provided in the product decription. If that is the case, then my solution will not work. Then OP would have to change to a real SPLITTER system.