[SOLVED] Controlling 3 pin fans via Splitter with molex power supply+4 pin connection to MOBO?

Jul 30, 2019
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Very specific question(coz i made a huge detective research already)

Plan : connect to MB with 4 pin(chassis fan 4pin) + molex for power supply from PSU + 3 pin fans. (why not just use hub?-i dont want to fry my MB coz it has 1amp limit yep and 4 3pin fans will use around that and jump on a pc start)
MB - asus z170p manual says
4-pin Chassis Fan connectors for 3-pin (DC mode) and 4-pin (PWM mode) coolers control
So the question is .... 3 pin fans connected this way(splitter...to MB...to PSU..) no extra 4 pin fan will be attached so i will Not Know the SPEED of fans but CAN I CONTROL THEM though, will there even be option to do DC mode control or stuck with 12v max throttle??

Thanks!
 
in bios u should have option to switch between PWM (4pin) and DC (3pin) modes, DC mode basicly lowers voltage, from 12V (full speed) to as low as your fan can handle (3V, 5V, etc)
but since u will be using molex for power, than DC mode will not work, because 12V will be provided from molex and not from mainboard

so your splitter will be handling fan control
if your fan splitter doesnt have fan control, then u may need one

for manual control there are basic ones with knobs
for automatic control (based on temperatures), u will need one with temperature sensors (not everyone has automatic control)
some also have usb connection for controling it through software
 
Reactions: GruesomeNoob
in bios u should have option to switch between PWM (4pin) and DC (3pin) modes, DC mode basicly lowers voltage, from 12V (full speed) to as low as your fan can handle (3V, 5V, etc)
but since u will be using molex for power, than DC mode will not work, because 12V will be provided from molex and not from mainboard

so your splitter will be handling fan control
if your fan splitter doesnt have fan control, then u may need one

for manual control there are basic ones with knobs
for automatic control (based on temperatures), u will need one with temperature sensors (not everyone has automatic control)
some also have usb connection for controling it through software
 
Reactions: GruesomeNoob
Jul 30, 2019
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iDC mode will not work, because 12V will be provided from molex and not from mainboard
when u said this.. its so obvious to me now(my head was boiling from ton of new info i googled lul)
about knobs controllers - good idea aswell i will prolly stick to it! was looking at STW 6041 pretty good for its price(20$) compared to all this stuff with cords(10$) and panicking about not killing MB etc
 
Unfortunately you have been caught in a problem many have stumbled over. The makers and sellers of these devices for connecting several fans to a single mobo header are TERRIBLY INCONSISTENT with their labels! They confuse Splitters and Hubs badly!

I prefer to label them according to their electrical design and FUNCTION, and NOT by their physical appearance. So to me a SPLITTER is a very simple device that merely connects all of the Ground and Voltage Supply leads from all of the fans to the appropriate mobo header pins: specically, all Grounds are fed from Pin #1, and all +DCV power lines are fed from Pin #2. Next, note that any mobo header can accept the speed pulse signal coming back to its Pin #3 from only ONE fan, so all proper Splitters will send back only ONE fan's speed signal, and ignore all the others by simply NOT connecting to the Yellow lines from the other fans. Assuming you are using a 4-pn Splitter, the PWM signal from Pin #4 of the header also is connected in parallel to all of the fans' fourth lines so they all get the same PWM signal. Note that the only source of power to all the fans is from the mobo header Pin #2, so the 1.0 A max curent draw limit of the header applies to the total of all the fans connected to this header. Physically, a Splitter may look like a group of several arms of wires, or like a small circuit board with header pins. It has only TWO types of "arms": a single cable to plug into the mobo header, and two or more output "arms" (OR headers on a board) to plug fans into.

A HUB is a different device. It gets all of the +DCV power for all its fans directly from the PSU, and for this purpose it has a third "arm" that must plug into an output from the PSU - either a 4-pin Molex or a SATA power output. This gets a fixed +12 VDC supply that is distributed to Pin #2 of ALL the connected fans, and those fans do NOT draw ANY power from the mobo header, so the 1.0 A limit does not apply. The Hub does connect all its fans' Ground lines to header Pin #1, and all the fans' PWM signal lines to header Pin #4, but this deos not overload the header. And like a Splitter, the Hub sends back to its host header the speed signal of only ONE of its fans. A HUB may also appear to be just a collection or wiring "arms" such as you have, or it may look like a circuit board with header pins, or like a closed box with ports along the sides. It's pretty hard to telll a
SPLITTER and a HUB apart from simple appearance.

So you can see, the way you CAN tell the difference between the two is the presence of that third "arm" on a Hub that must connect to a PSU power output. OP, if you look at that thing you got, it HAS this power connection arm ending in a 4-pin Molex male connector (with only two pins installed in it), so it is really a HUB as I label them. A SPLITTER has no such third "arm".

Now, the problem this causes is this. The ONLY way to control the speed of a THREE-pin fan is to vary the Voltage supplied to it from mobo header Pin #2. That method of fan speed control is called "Voltage Control Mode" or "DC Mode". But a FOUR-pin fan works differently. It gets a constant full 12 VDC supplied to it from mobo header Pin #2, and then also gets the PWM signal from Pin #4. Inside that fan is a small chip that uses the PWM signal to modify the flow of current from Pin #2 though the windings, thus altering the motor speed. This method of fan speed control is called "PWM Mode". But if you plug a 3-pin fan into a 4-pin header using this PWM Mode, it gets always full 12 VDC from Pin #2 and never gets the PWM signal from Pin #4 because it has no special chip to use that signal, anyway! So a 3-pin fan mis-connected this way always runs full speed - you have NO control of its speed.

NOTE that a HUB (such as you have) sends full 12 VDC power to all its fans on Pin #2 and the PWM signal on Pin #4, and its design depends on assuming you have only 4-pin fans. So it (and its associated mobo header operating in PWM Mode) can NOT control a 3-pin fan's speed. The ONLY device you can use to connect several 3-pin fans to a mobo header is a SPLITTER that does NOT send a fixed 12 VDC from the PSU to its fans, But this DOES mean that all the fans draw their power from the mobo header's Pin #2 and cannot draw more than 1.0 A total. (Actually, you CAN use a 4-pin SPLITTER with 3-pin fans, because they don't make any use of Pin #4 anyway.) What is important, though, is that the HEADER MUST be configured to use the older Voltage Control Mode (aka DC Mode), and NOT the new PWM Mode.

Now, OP, you are concerned about that 1.0 A load limit. You have not told us what fans you have, nor how many. Many simple fans draw 0.1 to 0.25 A each max, so up to four of those can be connected safely to a single mobo header. (By the way, apparently the small starting current surge of the motors is taken into account in that 1.0 A max current draw spec.) So tell us what fan maker and exact model number of fan you have, and how many. Then we can recommend how to power AND control them from the TWO CHA_FAN headers you have available. It might be one Splitter or two, or even a particular unusual Hub that can deal properly with 3-pin fans.
 
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Jul 30, 2019
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So tell us what fan maker and exact model number of fan you have, and how many. Then we can recommend
Wow that's a fullest answer i've ever had :D appreciate it, i know more now.
I have 4 deepcool xfan 120 fans, the problem is i can reach only to One of the 4 pin chassis headers on MB (my CPU cooling tower completely blocks the other one above it). This fans use 0.20±10%A i previously checked manufacturers website , so 4 will be 0.8-0.9 but what bothered me was this starting jump they might get which will exceed 1amp, short-term but still.

To avoid all this mess (knowing i can reach only to 1 MB header) i might just buy STW 6041 knob , connect it to PSU with molex and safely use and control all fans manually with DC(also, it can provide up to 30w to a single header so i can get even more fans if needed by Y-splitting some of cables) - seems like an old school method for 2020, but it should work :D
 
Something does not check. the Deepcool Xfan120 web page shows its current consumption as 0.07A each, or 0.28 A for four. That's only one-third of what you say. And that 0.07 A current looks reasonable for a quiet 120 mm fan that pushes at max 44 CFM. You should have NO problem powering and controlling all four from a single mobo header. One of these that looks like a circuit board with fan headers would do the job

https://www.newegg.com/black-en-labs-30cm-cable-splitters/p/1W7-0053-00002?Item=9SIACJF5528563&Description=fan splitter&cm_re=fan_splitter-_-9SIACJF5528563-_-Product

If you get that note these points:
(a) do NOT plug your CPU cooler into this. But DO plug one of your case fans into the output header marked CPU. That is the ONLY output that can returns its fan's speed to the host mobo header;
(b) ensure it is fastened down somewhere handy, not just able to float around loosely; and,
(c) the description says it will make 3-pin fans run full speed. Not true IF you configure the mobo fan port to use the older Voltage Control Mode (aka DC Mode).

Another option is to buy three simple two-output splitters like this

https://www.newegg.com/p/N82E16812423160?Item=N82E16812423160&Description=coboc fan splitter&cm_re=coboc_fan_splitter-_-12-423-160-_-Product&quicklink=true

and make a "stack". Plug two of them into the output arms of the third, and the stack turns one mobo header into four fan outputs. Or, if you buy two three-output Splitters similar and "stack" them, you get five outputs.

The issue with a manual Fan Controller module such as that STW 6041 is that it can do NO automatic control. It can show you up to four tempereatures if you connect and mount the sensors it includes, but those will never tell you the exact temperatures of the thing you need to know, which is the temp of the most important heat generator on your mobo (as decided by its maker, but not disclosed to you) OR its target temperatures. Most importantly, using that device makes YOU the controller - YOU must decide when and how to change fan speeds as your workload changes.
 
Jul 30, 2019
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Right, all u say makes perfect sense to me!
my apologies, i did not provide correct fan name. its xfan 120 l/w and not just xfan 120. Yikes. My bad - i thought only difference was white LED on l/w model but turns out its not only that but 0.07±10%A turns into 0.20±10%A and 43.56CFM > 65.16CFM along with x3 power consumption, looks like l/w is a new model.
Thank you so much for ur time and explanations!
 
Ah, that explains it! So your fans DO draw 0.20A each, total is 0.8 A for four if connected to a single header. Still that's OK. The short-term power surge during start-up is tolerable. By the way, these fans are called "LED Fans" since they contain only one colour of LED in the frame, and those LED's cannot be controlled separately from the fan motor. They are not RGB Fans. In LED Fans, the lights are simply connected in parallel with the motor and receive the same power (voltage supply) as the motor. So you may notice that, when the fans are running slower at low cooling requirements, the LED's are not full brightness.
 

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