Question Sys_fan header temperature sources

[anjris]

Hi

I have MSI Z390 A PRO motherboard. And want to know about sys_fan headers.

Does all 5 Sys_fan headers work on CPU temp or System Temp source?


On which Temp Source it will work?


Thank you

 

[Paperdoc]

On p. 64 of your mobo's manual it shows a general screen display apparently for ALL fan headers, but no further detail. That does indicate that you CAN choose which temperature sensor is used for EACH header separately, but it does not say exactly that for sure.

In general, from that screen you must select the specific header you want to configure. Then for that particular header you can make several settings. That includes which sensor is to be used to guide this header. For most uses of the SYS_FANn headers (that is, for case ventilation fans) this should be set to use the sensor on the Motherboard, and NOT the one onside the CPU chip. On rare occasions you plug something quite different into one of those headers (e.g., a AIO system pump) and so you have the option to choose the CPU internal temp sensor if necessary. There is no indication in the manual of what the default settings are.

After making all your changes, remember to use the F10 key to get to the Exit menu, and SAVE and EXIT.

 

[anjris]

On p. 64 of your mobo's manual it shows a general screen display apparently for ALL fan headers, but no further detail. That does indicate that you CAN choose which temperature sensor is used for EACH header separately, but it does not say exactly that for sure.

In general, from that screen you must select the specific header you want to configure. Then for that particular header you can make several settings. That includes which sensor is to be used to guide this header. For most uses of the SYS_FANn headers (that is, for case ventilation fans) this should be set to use the sensor on the Motherboard, and NOT the one onside the CPU chip. On rare occasions you plug something quite different into one of those headers (e.g., a AIO system pump) and so you have the option to choose the CPU internal temp sensor if necessary. There is no indication in the manual of what the default settings are.

After making all your changes, remember to use the F10 key to get to the Exit menu, and SAVE and EXIT.

Thanks for your response. But under hardware monitor section in BIOS. I m not getting the option to change the temperature source. It wS showing just PWM OR DC MODE. So how should i change the temperature source of each header.

And MSI told me that all sys fan header including cpu header as well it will use inside cpu temp. Not the motherboard sensor.

So any other suggestion how can we achieve this?

 

[Paperdoc]

If there is no way to specify what temp sensor is used by the mobo SYS_FAN headers, you cannot change it. BUT I suspect strongly that the MSI Tech Support person told you wrong! What you were told is NOT very likely. Almost all mobos are designed to use a temp sensor on the mobo for the SYS_FAN (or CHA_FAN on other boards) headers, quite separate from the sensor built into the CPU chip. But since you cannot change it anyway, you can just stop worrying.

 

[anjris]

If there is no way to specify what temp sensor is used by the mobo SYS_FAN headers, you cannot change it. BUT I suspect strongly that the MSI Tech Support person told you wrong! What you were told is NOT very likely. Almost all mobos are designed to use a temp sensor on the mobo for the SYS_FAN (or CHA_FAN on other boards) headers, quite separate from the sensor built into the CPU chip. But since you cannot change it anyway, you can just stop worrying.

Right. I was curious to know because no one can confirm in this world. What temp source the SYS_FAN header will work on? CPU or Motherboard temp?

 

[rascalov]

System fans (case fans) are controlled from BIOS/UEFI with PWM and show you the RPMs if it has 4 pin connector connected to 4 pin header. Fans with 3 pin connector connected to 3 pin header will show you only the RPMs not temperature. If you just want to run full speed your fans, you should plug in directly with molex (2 pin) to power supply cable.
You said about temperature on your motherboard. The temperature of your motherboard is measured at chipset. And your CPU has internal thermal sensors on each core and general sensor on the chip.

 

[anjris]

System fans (case fans) are controlled from BIOS/UEFI with PWM and show you the RPMs if it has 4 pin connector connected to 4 pin header. Fans with 3 pin connector connected to 3 pin header will show you only the RPMs not temperature. If you just want to run full speed your fans, you should plug in directly with molex (2 pin) to power supply cable.
You said about temperature on your motherboard. The temperature of your motherboard is measured at chipset. And your CPU has internal thermal sensors on each core and general sensor on the chip.

I am not sure before replying why no one is reading the previous reply.

I am asking What temp source the SYS_FAN header will work on? CPU or Motherboard temp?

 

[anjris]

I am not sure before replying why no one is reading the previous reply.

I am asking What temp source the SYS_FAN header will work on? CPU or Motherboard temp?

On what basis, sys fan RPM will get regulate automatically.

As i know CPU fan RPM will get regulated by sensing CPU temp. what about SYS FAN Headers. on which temp source they will work( CPU temp or SYstem Temp)

 

[Paperdoc]

As I said previously, virtually ALL mobos have at least one temperature sensor built into the mobo at some point the designers have decided is either typical of the whole mobo, or a critical component whose temperature needs first priority. In addition, the CPU maker has installed at least one sensor inside the CPU chip. On every mobo I've looked at recently, the internal CPU sensor is the ONLY one used for the CPU_FAN header. On some mobos you have the option to use that same sensor for other fa headers. Then for all the CHA_FAN or SYS_FAN headers you always have the option of using the mobo temp sensor to guide them. In many cases (such as yours) you have NO other option, so I'm pretty sure in your case it is the mobo sensor used for the SYS_FAN headers.

rascalov has things mixed up a bit. For both CPU_FAN and SYS-FAN headers the normal automatic fan control strategy is to establish a target temperature for the relevant sensor and a few control loop tuning parameters (pre-programmed settings) and constantly monitor the actual temperature st that sensor. If that measurement deviates from the target, the BIOS control software changes the speed of the fan its is controlling. It makes further changes if that is insufficient or if the measured value changes. VERY often you have three other choices. One is that you can set your own target and acceptable temperature range (a "custom fan curve") that works in exactly the same manner but with different control parameters. The other two are usually fixed speeds with NO speed control changes - either full speed or some reduced speed.

Virtually all fans generate within the motor a speed signal consisting of two brief 5 VDC pulses per revolution and send that out on Pin #3 of the fan cabling. The mobo counts those to display fan speed and as a secondary function, checks to be sure that there IS a speed signal coming on - no speed signal (or, on some cases, a speed below some limit) it treated as a fan FAILURE and are warnings sent out. But in fact the speed is NOT used to control the fan speed! The target of the automatic control system is the measured TEMPERATURE, not the fan speed. BOTH 3-pin and 4-pin fans DO send exactly the same type of speed signal on the same pin back the the mobo header.

The older type of fan called 3-pin or Voltage Controlled Fan has its speed controlled when the mobo varies the voltage supplied to it (on Pin #2 - #1 Ground) from 12 VDC for full speed down to about 5 VDC. Any lower voltage may cause the fan to stall. The newer PWM fan design (4-pin fan) requires a different method to control its speed. In this system, the Voltage supplied on Pin #2 is always 12 VDC, and there is a new PWM signal on Pin #4. Inside the motor case there is a small chip that uses the PWM signal to modify the flow of current from the +12 VDC supply though the windings, thus providing speed reduction to whatever is needed. The design of the two systems means that if you mis-match systems and plug a 3-pin fan into a 4-pin header that actually is using PWM Mode as its method of speed control, that 3-pin fan receives the constant +12 VDC from Pin #2 and no PWM signal because it has no connection to Pin #4, and has no chip to use it, anyway. So that fan will always run full speed - you get lots of cooling, but no ability to reduce fan speed. IF you mis-match the other way - connect a 4-pin fan to a header using the older Voltage Control Mode (aka DC Mode), the fan will receive no PWM signal because the mobo does not send one out on Pin #4,but it will receive on Pin #2 a VARYING voltage that DOES control the speed of the fan.

Most mobos now use only 4-pin headers for fans, but that does NOT mean they are using the new PWM Mode always. IF a mobo is designed for it, the Mode (method of speed control ) may be chosen - either Voltage Control Mode or PWM Mode - and very often is set to default to PWM. So such a header CAN control the speed of EITHER type of fan if its configuration is set properly. However, some header do not offer this flexibility and use only one of those Modes. But in any case, BOTH types of headers CAN read and display the speed of the fan IF the fan actually has the wire to carry the speed signal to header Pin #3.

So, all the statements you see claiming the you cannot control or "see" the speed of a 3-pin fan no matter what are wrong. You can not control that fan's speed IF the mobo header cannot use the older Voltage Control Mode, but you can if that choice of Mode is available in the header's configuration. And both types of header Mode can control the speed of 4-pin fans, even if technically the Voltage Control Mode is not as good as the new PWM Mode for 4-pin fans.