Question Motherboard or Fan controller for 3 pin case fans

Apr 4, 2020
Hi All,

Hope you are keeping well during these difficult times.

I was hoping I could get some help regarding fan controllers.

I have a 10 year old pc, where the 3 case fans (2x 120mm and 1x92mm) are wired into the PSU molex plugs. I have no idea why 2 of the fans were powered like this as the motherboard has 2x 3 pin chassis fan connectors. Anyway, this makes the fans always run at 100% and so they are very loud, which is why I hardly ever use my desktop.

I wanted to know if I get 2 new 120mm “silent” fans, should I plug them straight into the motherboard and use bios to control their speed, or connect all three fans to a fan controller and manually control the speed. If I go the fan controller route, should the CPU fan still be connected to the motherboard?

Also, I wanted to know if 4-pin fan controllers regulate the speed of 4-pin fans via voltage or PWM. This is because if the fan controller's automatic setting does regulate speed of the 4-pin fans via PWM, then I will get 4-pin fans in order to take advantage of the automatic setting. If however the speed is adjusted via voltage only, then I will just get 3-pin fans.

Thank you.


3pin voltage fan controllers are very hard to find as it takes physical circuitry to regulate voltages. Far easier and cheaper to get pwm 4pin controllers that only need a small circuit board to regulate a pwm signal.

If you get 3pin fans, plug them into the motherboard, most 3pin nowadays are efficient enough that 2 can be used on a splitter and that is usually a better idea if controlling 2 intake fans or 2 top exhaust etc. Keeps the fans in a group regulation.
Reactions: satty89


The speed of a 3-pin fan can be controlled ONLY by varying the voltage supplied to it. The new 4-pin fan's design means it is best to use the new (and different) PWM Mode to control its speed. BUT as a backwards campatibility feature, one CAN use the older Voltage Control Mode (aka DC Mode) to control the speed of a 4-pin fan - it's just not ideal.

OP, I'm guessing you have an slightly older mobo. And here's where it gets tricky. The NUMBER of pins on a mobo header does NOT necessarily tell you what control Mode it is going to use. IF the header has only thee pins, then it can ONLY use the older Voltage Control Mode REQUIRED by 3-pin fans, but OK for 4-pin ones, too. If the header has 4 pins (virtually all headers on newer mobos are like this), there are several possibilities for what it does.
(a) It may be able only to use the new PWM Mode of control, so any 3-pin fan connected to this will always run full speed.
(b) It may actually use only the older 3-pin fan Voltage Control Mode despite its pin count. Because the new 4-pin fans can work with that, this header type can work for either fan type with no effort.
(c) Within BIOS Setup, the options for configuring such a header may offer you a choice of whether to use older Voltage Control Mode or new PWM Mode. You set this for each fan header separately according to the type of fan you have plugged in there. Note that the initial Default setting of this may not be correct for your fan, so it should be checked.
(d) Again in BIOS Setup, if the choice of Modes is available, some offer an "auto" option that claims to detect the fan type connected and adjust itself. But note that some early versions of that really used option (b) above - use only 3-pin mode and rely on having 4-pin fans work with that.

OP, if you tell us the maker and exact model number of your mobo, we can look up its specs and advise what fan types it can deal with.

I'm not clear from your post about your CPU cooler fan. And this links to what fan header groups you have. Virtually all mobos have two groups that differ in an important detail of the automatic fan speed control systems. By the way, these really are TEMPERATURE controls - that is, the focus is on the temperature actually measured by a sensor, and the fan speed is merely the tool that the system uses to control the temperarure at the sensor. There is always a CPU_FAN header. It always uses a temp sensor built into the CPU chip itself by its maker to guide the automatic control of the CPU cooling system. Separately there are one or more CHA_FAN or SYS_FAN headers intended for case ventilation fans, and they use a different temp sensor built into the mobo by its maker. So it's always good to connect a fan to the correct header, dependent on what it is cooling. In some mobos, the headers for the case fans may also offer you a choice of which sensor to use. Some allow you to choose the CPU chip's internal sensor if you need to. Some also have extra sensors on specific mobo components for use if you are setting up a fan dedicated to cooling that specific mobo area.

So, OP, you do have a CPU cooler, and I'm not clear where it is attached - maybe the CPU_FAN header. Then you have two or three case ventilation fans and so far they all are connected to PSU Molex outputs. For each of these, tell us how many wires come out of the fan motor to the connector. Further, is the connector on the end of those wires a male 4-pin Molex (with round pins inside a shroud) or a female standard fan connector (about 3/8" wide with three holes, and ridges running down one side)? (Some fans also were sold with both types of connector on the wires from the fan motor for flexibility). The wire count and connector type have a real bearing on how you can re-use or replace them.

You say the mobo has two 3-pin chassis fan headers. Is that in ADDITION to the CPU_FAN header?

Assuming for the moment that your mobo does have the commonly-available options for controlling its fans via its headers, you probably do not want a Fan Controller. These are third-part add-ons you mount in your case front. By far the majority of them use only the older Voltage Control Mode irrespective of the pin count on their output connectors. The majority are strictly manual controllers. That is, YOU are the controller who must monitor your system's cooling needs and choose when to change the fan speeds, and to what new value? If you want automatic control of speeds based on actual measured temperatures, you should use the mobo facilities. We just have to ensure you get the right fans and Splitters for that job.



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