Question About 3/4 Pin Fan Headers/Adapters

Apr 22, 2019
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Hi so recently I decided to get a new PSU (Corsair TX650M) for my pre-built PC (which previous had a dodgy Thermaltake Litepower 650W). I installed it and everyone was going fine but then my LED fans (no-name brand) started flickering on and off. I thought it would stop but it didn't. I believed the cause was that the fans were receiving too much power from the new PSU, and since three fans were connected to one slot (SYS_FAN2) on the motherboard. So I powered off my PC and checked the fan headers and cables, which I knew nothing about. I noticed that I had a three-to-one adapter for the three fans to go straight to the mobo. Could someone tell me the name of this adapter? I also noticed that one pin from two of the heads was missing. Is it broken? Is it safe to plug three fans into one SYS_FAN slot? Why am I plugging a fan header with three pin slots into a 4-pin connector? Thank you for reading :)
EDIT: Found out that it is safe plugging a 3-pin header into a 4-pin socket.
EDIT: Found out the name of the adapter: "PWM 4Pin To Dual PWM Y-Splitter"
EDIT: I also have a fan at the back of the case, which is connected to the SYS_FAN1 slot and doesn't flicker. I just bought two Y-splitters off ebay so that two can go into SYS_FAN1 and two can go into SYS_FAN2. Hopefully it lightens the load on the SYS_FAN2 slot.
Last edit (im basically answering this all on my own lol): Found out that the rear case fan should be attached to SYS_FAN1 on its own to maintain a good RPM. This means I should buy a new 3-way 4-pin adapter for SYS_FAN2 because the pins on it seem to be broken.





 
Last edited:

Lutfij

Titan
Moderator
When posting a thread of troubleshooting nature, it's customary to include your full system's specs. List them like so:
CPU:
Motherboard:
Ram:
SSD/HDD:
GPU:
PSU:
Chassis:
OS:

On a second note, you might want to include the make and model of the fans used and how you've connected them to the board. You should also include a link to the PWM splitter you have at hand.
 
Apr 22, 2019
87
7
45
1
When posting a thread of troubleshooting nature, it's customary to include your full system's specs. List them like so:
CPU:
Motherboard:
Ram:
SSD/HDD:
GPU:
PSU:
Chassis:
OS:

On a second note, you might want to include the make and model of the fans used and how you've connected them to the board. You should also include a link to the PWM splitter you have at hand.
Sorry about that.
CPU: Intel i5-8400 2.8GHz
Motherboard: MSI B360M Bazooka
Ram: 2x4GB GeIL EVO FORZA 2400MHz
SSD: WD Green 240GB M.2
HDD: Seagate Barracuda 2TB
GPU: ASUS Radeon 4GB RX 570
PSU: Corsair TX650M (new)
Chassis: Rotanium TG301 (basically unbranded)
OS: Windows 10 Home

I honestly don't know the brand of the fans. They have some sort of flame logo on them though. I connected the front three to the SYS_FAN2 header using this adapter. The rear fan is connected directly to the SYS_FAN1 header (one pin is left out because it is 3-pin to 4-pin, same with the other three).
 
You already know that you can plug 3-pin fans into 4-pin fan headers. HOWEVER, you may not get what you expect that way. Assuming the 4-pin header actually is using the newer PWM Mode of control (some are not, even though they have 4 pins), a 3-pin fan connected this way will always run full speed - that type of header Mode can NOT control the speed of a 3-pin fan. IF your mobo allows you (in BIOS Setup) to configure the header to use Voltage Control Mode (aka DC Mode) instead, that Mode CAN control the speed of both 3- and 4-pin fans.

Now, number of fans on a single header. Almost all such headers can supply up to 1.0 A current to the total of all its fans. Most fans today consume under 0.2 A, so three on a header is OK. BUT you talk about using fans that have LED's built into them. LED Fans were the first lighted fans to market. They normally have only one colour of light in them that you can NOT control in any way, and there is only one electrical cable from the unit that plugs into a mobo fan header. In those units the LED's are wired in parallel with the motors, and thus they add to the current load. The result is that many LED Fans consume about 0.35 to 0.5 A each, so three of them on one header is NOT allowed. Splitting them up as two on each of two headers is quite all right. I don't know why you believe that the rear fan should be the ONLY fan on that SYS_FAN1 header. Your problem was not that the new PSU gave the fans too much power. It was that the three LED fans on one SYS_FAN2 header could not get enough power from that header.

Now to your concern about missing pins. Every fan generates a speed signal (2 pulse per revolution) that is sent back to the mobo header on the yellow wire via Pin #3 where it is counted to give a speed reading. But the header can only handle a speed pulse signal from ONE fan - more than that causes huge confusion, wrong readings and error messages. So any proper Splitter will send back the speed of only ONE of its fans, and completely ignore any others. To do that, the simplest way is just NOT to provide a connection for the Pin #3 line at the output arms of the Splitter for more than one output - hence the missing Pin #3 of some output arms. This has NO impact on ability to control fan speeds, but it does mean that some fan's speeds are NOT being monitored for FAILURE by a mobo header.

Go back to two fans each on two headers, and don't worry about missing Pin #3 on the Splitter output arms. Check in BIOS Setup (see mobo manual p. 59) for each SYS_FAN header at the left side. The manual suggests that the SYS_FAN headers both will already be set by default to DC. If that is correct, you can just leave it. IF you have to change it to DC, make sure you SAVE and EXIT to get out. DC Mode will control the speed of your 3-pin LED fans. However, one normal characteristic of this fan type is that the brightness of the LED's may dim when the fan is running slowly.
 

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