[SOLVED] Why do some pwm fan splitters have a 3 pin end while other types have 4 pin ends ?

[knowledge2121]

Looking at this splitter:

As you can see, only one end has 4 pins ... the other two ends have 3 pin, The 3 pin ends have the tach pin missing because only one fan can send back the RPM/tach signal and it is the fan connected to the 4 pin end ...

Now look at this splitter:

Why does this adapter have only 4 pin ends ? Wont this confuse the motherboard ?

 

[Lutfij]

Please read this;

Help me here - "PWM" fan splitter with only 3 pins?

So I've just bought an Akasa PWM fan splitter, one of the connectors has 4pins as you would expect, but the other one only has 3 pins instead of 4. I'm not overly familliar with PWM, having previously stuck to 3pin manually controlled fans, but wouldn't this make it "non-PWM"? At first I...

forums.tomshardware.com

and this;
https://www.quora.com/Is-it-normal-...-that-still-work-with-PWM/answer/Drazen-Zoric

As for your PCB mounted PWM splitter, please stay away from them since they often tend to be devoid of additional power input which can and will damage the PWM fan header on the motherboard.

 

[Paperdoc]

As the links given you by Lutfij say, the Splitter's output connectors are arranged so that the speed signal from only ONE fan is sent back to the host header on the mobo. The reason is that the signal; consists of short pulses of 5 VDC, 2 per rotation of the fan. The header simply counts those pulses to get sped. But it cannot deal with TWO trains of pulses form different fans - the counts vary wildly, causing weird readings and errors. So all Splitters and Hubs will do this. Now, some such devices like that circuit board do it differently. They include all the pins on the header or connector, but inside in their circuit boards they just do NOT connect the speed signals via Pin #3 from most of the fan output headers. Then they DO mark the ONE header whose speed signal is sent back with some label - often "CPU" to suggest that the CPU fan should be plugged into that output header. But actually connecting THAT fan there is ONLY to be done when the Splitter is plugged into the CPU_FAN header of the mobo. When is it used just for case ventilation fans, you just need to plug into that marked port one of the case fans.

I'll offer a different caution on that circuit board Splitter. A SPLITTER is a simple device that merely connects all of its outputs in parallel to the feed from the mobo fan header (except, as in this discussion, the speed signals) so that ALL of the power for the fans is drawn from that host header. MOST mobo fan header are limited to supplying up to 1.0 A current to the total load. Most case fans draw 0.1 to 0.25 A max each, so using a Splitter like that for 3 or 4 fans on one header is usually acceptable, as long as you DO check the fan specs and verify the total load. A SPLITTER can be used both with older 3-pin fans and newer 4-pin fans. Because of the backwards compatibility features of 4-pin fan design, you CAN use a 4-pin Splitter for both fan types.

A HUB is a different device that gets all of the power for its fans directly from the PSU. It has an extra cable that plugs into a PSU output for this - that's how you can recognize a Hub. It takes NO power from the mobo fan header, so that avoids the 1.0 A limit. BUT it operates by distributing to all its fans the PWM speed control signal from Pin #4 of the host header. That means that this device is able to control the speed of its fans ONLY of all those fan s are of the new 4-pin PWM design. Any 3-pin fan plugged into a HUB will always run full speed.

Both Splitters and Hubs MAY appear to be a collection of cable arms, or a small circuit board, or a closed box with ports recessed inside the holes of the case. You can NOT tell one from another by the form. You CAN tell from the existence of the extra connection cable to a PSU output (for a HUB) or it absence (for a SPLITTER).

 

[hotaru.hino]

The other fan headers lack the RPM sense pin. This is to prevent confusing the motherboard what the RPM is as every fan is not going to be spinning at exactly the same speed or in the same starting point when the fan begins to turn.

See https://allpinouts.org/pinouts/connectors/motherboards/motherboard-cpu-4-pin-fan/. Obviously the headers can't be missing pin 2 which is the 12V pin. Instead they're missing pin 3, which is the RPM sense pin.

 

[knowledge2121]

1. Why are the pins on the CPU_FAN header labeled differently than the rest of the fan headers?

gnd-12v-sense-speed control
vs
gnd-speed control-sense-vcc

??? Do all of the fan headers support pwm mode ?

2. If i connect a pwm 4pin fan to SYS_FAN, The fan runs in pwm mode and if i connect a 3pin fan, it runs in voltage mode ? Am i correct ?

3. Whats the maximum current that CPU_FAN, CPU_OPT and each SYS_FAN can provide ?

 

[Paperdoc]

According to the labels you show from that manual, ONLY the CPU_FAN header acts as a complete 4-pin PWM mode header. In that system the power on Pin #2 is always 12 VDC, and the 4-pin fan has a special chip that uses the PWM signal from Pin #4 to modify the flow of current from the 12 VDC supply though the motor windings to achieve speed control. All of the other headers have 4 pins, BUT the signals on them are all for the older 3-pin voltage Control Mode. In that system, the Voltage on Pin #2 us varied from 12 VDC for full speed sown to about 5 VDC for minimum speed without stalling. From the labels I would guess that in BIOS Setup there is NO option on any of these headers to change any of them to the other signal Mode.

One of the important backwards compatibility features designed into the 4-pin PWM fan system is that if you plug one of them into a 3-pin fan header using that Voltage Control Mode it gets NO PWM signal and so its chip cannot modify power flow from the source on Pin #2. BUT that source has Voltage that VARIES - is NOT always 12 VDC - so the speed of the fan IS controlled in this mode, even though it is not using the PWM system. This was a wise choice to simplify the introduction of PWM fans to a market full of mobos with NO 4-pin headers to provide PWM signals. Users would NOT have any trouble using the new fans on an older mobo. In your mobo, all the headers except CPU_FAN send out signals exactly like a 3-pin fan system would do, but from a 4-pin header. So this backwards compatibility feature in any 4-pin fan means those fans WILL work properly on this mobo.

This scheme does have one small gotcha! that you have avoided. IF you had tried to use a HUB in your system, it would NOT have received any PWM signal to send out to its fans of whichever type. Meanwhile, it would NOT get any varying Voltage from the host header Pin #2 because it feeds to ALL of its fans a fixed 12 VDC directly from the PSU. So ALL fans on a HUB used with this mobo (except if used with the CPU_FAN header) would always run full speed.

 

[knowledge2121]

I have this hub.

What if i connect ALL of the fans(CPU fans + Case fans) to the hub and then connect the hub to the CPU_FAN header which has pwm support ?


Edit: what happens if i can actually set the SYS_FANs to pwm in the bios ?

https://noctua.at/en/how-can-i-check-if-my-4-pin-fan-header-supports-pwm

Please also note that in some cases, the descriptions of the pin layouts in the mainboard manuals may not be correct and some models actually allow you to switch the fan headers from voltage control mode to PWM control mode in the BIOS even though the pin descriptions do not indicate PWM support. We thus recommend to look for these options in the BIOS before taking other measures. In case of doubt, please contact your mainboard manufacturer.

 

[hotaru.hino]

1. Why are the pins on the CPU_FAN header labeled differently than the rest of the fan headers?

gnd-12v-sense-speed control
vs
gnd-speed control-sense-vcc

??? Do all of the fan headers support pwm mode ?

It's labeled differently for identification purposes. How do you know which fan header you're setting the behavior to in BIOS if you don't know which one you're poking at? Although the CPU_FAN header usually gets special treatment in that if the computer doesn't detect a fan (usually by applying 100% to the fan and seeing if it detects an RPM signal), it'll warn you about it.

2. If i connect a pwm 4pin fan to SYS_FAN, The fan runs in pwm mode and if i connect a 3pin fan, it runs in voltage mode ? Am i correct ?

Yes. This also applies to the CPU_FAN header.

3. Whats the maximum current that CPU_FAN, CPU_OPT and each SYS_FAN can provide ?

Typically 1A

I have this hub.

What if i connect ALL of the fans(CPU fans + Case fans) to the hub and then connect the hub to the CPU_FAN header which has pwm support ?

All of the fans will be controlled by the CPU_FAN curve. However, you cannot mix and match PWM and voltage controlled fans on a hub like this. If you do, either the other type won't work or it'll be at 100% all the time.

Edit: what happens if i can actually set the SYS_FANs to pwm in the bios ?

You can't. BIOS figures out which fan type it is on boot up.

 

[knowledge2121]

All of the fans will be controlled by the CPU_FAN curve. However, you cannot mix and match PWM and voltage controlled fans on a hub like this. If you do, either the other type won't work or it'll be at 100% all the time.

All of my fans are 4pin pwm fans...

Which way is it better:

Connect ALL fans to the hub and the hub to CPU_FAN

or

Connect case fans to the hub and the hub to SYS_FAN and CPU cooler fans to CPU_FAN ?

Is it better to speed control all fans at once or the case fans separately ?

 

[hotaru.hino]

All of my fans are 4pin pwm fans...

Which way is it better:

Connect ALL fans to the hub and the hub to CPU_FAN

or

Connect case fans to the hub and the hub to SYS_FAN and CPU cooler fans to CPU_FAN ?

Is it better to speed control all fans at once or the case fans separately ?

It depends on what you want.

I prefer my CPU fans controlled separately from the rest of the system, because my CPU fans don't need to spin up that fast to keep the processor cool, but I would like my case fans to be adjustable because I need them to move air when I'm playing a game, but not when I'm just browsing the internet or something.

 

[knowledge2121]

One more thing....the following picture from the mb manual proves that the SYS_FANs are pwm:

Can you also confirm this ?

Many thanks

 

[hotaru.hino]

One more thing....the following picture from the mb manual proves that the SYS_FANs are pwm:

Can you also confirm this ?

Many thanks

If it's a header with four pins, then it can control fans via PWM. There's no other configuration that I'm aware where it's not the case.

 

[Paperdoc]

Sorry, I find many things above incorrect. But first to OP's points.

1. OP, that Arctic Case Fan Hub you linked to IS a real fan HUB. It gets all fan power at a fixed 12 VDC from the PSU via a SATA power output. It gets the PWM signal from a mobo header via a cable to that header. IF it has those connections it CAN control all of their speeds according to that PWM signal.

2. To accomplish that, you will need to connect that hub to your CPU_FAN header, then plug your actual CPU cooler system into its Port #1, the only one that reports its speed to the mobo header. The result is that ALL your fans will be controlled according to the cooling needs of the CPU chip. Now, ideally your CASE vent fans ought to be controlled according to a mobo temperature sensor that your mobo's SYS_FAN headers use, but those headers can NOT provide a PWM signal to this Hub (see below). However, using the CPU_FAN header for all fan guidance is not unreasonable because there is a correlation between the workload (and heat generation) of the CPU chip and the accompanying workload of the rest of your system.

3. You have not told us how many CASE VENT fans you are trying to connect. As I said, you CAN connect more than one fan to EACH of your three SYS_FAN headers if you use SPLITTERS but those headers appear to use only the older 3-pin fan Voltage Control Mode. This WILL control the fans' speeds, whether they are 3-pin or 4-pin, even though technically this is not the ideal method to control a 4-pin fan. But that would mean control of those by the mobo temperature sensor. The LIMIT on doing this is that each header can only provide up to 1.0 A max current to the total load connected to it, so YOU must add up the max current specs for fans used via a Splitter for each header. IF you go this route, you will NOT be connecting anything to the CPU_FAN header except its cooler, so you would not need that Hub.

4. There is a third option. There is ONE unusual HUB sold by Phanteks called their Phanteks Universal Fan Controller.

https://www.amazon.com/Phanteks-Universal-Fan-Controller-PH-PWHUB_02/dp/B07NHQRCRM/ref=sr_1_1?crid=205MOCUQR3EQ7&keywords=phanteks+universal+fan+controller&qid=1654655283&sprefix=phanteks+universal+fan+controller,aps,262&sr=8-1

One of its unique features is that you CAN connect it to a mobo fan header that uses the older Voltage Control Mode, and it will translate that signal into a PWM signal it can provide to its four ports designed for use with true 4-pin fans, AND to Port #1 (the only one that reports speed to its host header) with the note that this one port automatically will detect what fan type is plugged in there (3- or 4-pin) and adjust itself to provide the right signal set. So IF you want to use a HUB to provide lots of power to many fans, rather than using Splitters, and you want them to have PWM signals for 4-pin fans when connected to a mobo header that does NOT provide PWM, this Hub cab do that job.

5. Almost all mobos now use 4 pins on ALL fan headers, but what signals those provide varies. Most recent mobos have options on each fan header to choose whether it outputs signals as Voltage Control Mode (aka DC Mode) or PWM Mode, and often an option for Auto Detect. This latter is supposed to test its connected fan at each start-up and set itself to the correct Mode, but sometimes that fails. As noted on the Noctua site, some mobo manuals show header labels that indicate ports do NOT have these options (as is your case, OP), but the options actually DO exist if you go looking into the header options in BIOS Setup. So you can do that check, OP, just in case.

Now to what I consider errors above.

6. The fact that a header has 4 pins does NOT prove it uses PWM Mode. BOTH modes can be done on a 4-pin header. But a 3-pin header can ONLY do the older Voltage Control Mode.

7. SOME mobo headers can detect which fan type is connected and adjust themselves to put out the correct signal type. They do this at star-up by outputting PWM signals and observing whether the fan speed changes. A 3-pin fan fed such signals can only run full speed all the time, so that's the test. But that can happen ONLY if the header is designed to do both possible Modes AND has that Auto Test function built in. NOT all mobo fan headers can do this.

8. If you connect a 3-pin fan to a header using PWM Mode, it can only run full speed, If you connect a 3-pin fan to a normal HUB which ONLY operates in PWM Mode, it will always run full speed, even though any 4-pin fans on this HUB WILL have their speed controlled.

9. The truth is that what a fan header does is control the speed of its fan according to the TEMPERATURE measured at a sensor in a suitable location. It does NOT care what that speed is - it only changes the speed to achieve a temperature target. In the fan configuration screens you get various ways of setting how fan speed will be set versus measured temperature. The speed may be labelled as a speed, a Voltage, a %, or a PWM number. But in reality it is putting out a % of maximum speed signal. The max signal is either 12 VDC (Voltage Control Mode) or 100% On for PWM Mode. In your manual, OP, they use the term "2.5 PWM Value per C", but that does NOT indicate that it is using PWM Mode. It's just a way of expressing the range of settings you can select.

 

[hotaru.hino]

6. The fact that a header has 4 pins does NOT prove it uses PWM Mode. BOTH modes can be done on a 4-pin header. But a 3-pin header can ONLY do the older Voltage Control Mode.

If the 4-pin header doesn't support PWM, then what else does it support?

7. SOME mobo headers can detect which fan type is connected and adjust themselves to put out the correct signal type. They do this at star-up by outputting PWM signals and observing whether the fan speed changes. A 3-pin fan fed such signals can only run full speed all the time, so that's the test. But that can happen ONLY if the header is designed to do both possible Modes AND has that Auto Test function built in. NOT all mobo fan headers can do this.

Considering every motherboard I've used in the past 12 or so years of various pricing levels could automatically detect what type of control can be used on the fan, I find it weird that these motherboards fall into the "some" category.

I mean, if you want, throw some motherboards my way that didn't have fan headers where you had to set which control type to use.

EDIT: I did go back and look at some of the motherboards I've used over that time period and I'll bite, some of them had an explicit PWM/Voltage control setting for the SYS_FANs. Otherwise the CPU_FAN was typically defaulted to automatically detecting what fan it is. However some of the boards did have an automatic detection option.

 

[Paperdoc]

hotaru.hino, your first question is answered by the second. As I said, most mobos now design their fan headers to output signals in EITHER (3-pin Voltage Control Mode) or 4-pin (PWM) Mode. In 3-pin Mode the signals are: Pin 1 Ground, Pin 2 +VDC (varying to control speed), Pin 3 Speed signal sent back to header, Pin 4 no signal or fixed voltage. In 4-pin Mode they become Pin 1 Ground (unchanged), Pin 2 +12 VDC fixed power (different), Pin 3 Speed signal (unchanged), Pin 4 PWM signal the fan uses to control speed. So that 4-pin header CAN be configured for either Mode.

You confirm that some older mobos had configuration options for these possible Modes. OP's mobo manual clearly indicates that that mobo (presumably even older) had NO choices: the CPU_FAN header used ONLY PWM Mode, and the SYS_FAN headers only Voltage Control Mode.

You are right that for quite some time now the CPU_FAN headers all have had both options AND most also have an automatic configuration option for that header.This design makes it easy for any user to plug in any CPU cooler system and get optimal control without knowing how to configure. That made them "universal" in terms of fan type selection. But for SYS_FAN headers those options were not always present. In fact, in the early days of introduction of PWM fans, many mobos used a different "trick" to achieve apparent "universal" capabilities for SYS_FAN headers. The used 4-pin headers but ONLY in 3-pin Voltage Control Mode, as OP's mobo manual says. This DOES control the speed of either fan type because the new PWM fan design includes a backwards compatible feature to ensure that. It has the hidden gothcha! that this trick can NOT be used with a HUB that requires a 4-pin PWM signal system.

Users of older mobos still have to navigate through these details. Fortunately almost all current designs use the techniques of two-option Mode designs and automatic configuration to achieve true universal optimal configurations with no need for the user to figure out anything. In more complicated cases (e.g, mixing fan types or large numbers of fans) the details become issues, but most users never have to worry.

 

[knowledge2121]

I guess i have to plug in a pwm fan into a SYS_FAN header and see if i can set it to pwm mode in BIOS.

If i couldnt, i have two options:

1. Plug all the case fans into the hub and have them run at 100% speed.

2. Since my fans are all P12 PWM PST types and their max current is 0.08A i can daisy chain them and connect all of them to a SYS_FAN header... this way i can voltage control them...