[SOLVED] 3 pin case fan on 4pin cpu fan header?

Solution
First, let's keep the uses of the mobo fan headers clear. That mobo has one CPU_FAN header, two for water pumps (one designated for AIO systems like you have, and another for other pumps) and two CHA_FAN headers. In general, the CPU_FAN header can ONLY use the temperature sensor inside the CPU chip to guide its automatic control of its fan, and that makes sense because its ONLY function is to cool that chip. Very often the two pump headers also are restricted to using that sensor. On the other hand, the normal configuration of the two CHA_FAN header is to use a different sensor for guidance - one on the mobo - since these are intended for case ventilation general use, and NOT for cooling the CPU. So it is these CHA_FAN headers you...

DavidM012

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Yes 3pins work on the 4 pin header but don't have the sense wire I think so there isn't as much speed control. All my fans are 3 pins on 4 pin headers and all I can do to control the speed is switch on monitoring in the bios which seems to cut the rpm to some degree or if monitoring is disabled they spin up full speed. The other setting such as silent or the rpm threshold controls in the bios simply don't do anything there is no circuit to control the speed.

That would be the CPU/CHA FAN PWM pin.
 

hich96

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May 10, 2019
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Yes 3pins work on the 4 pin header but don't have the sense wire I think so there isn't as much speed control. All my fans are 3 pins on 4 pin headers and all I can do to control the speed is switch on monitoring in the bios which seems to cut the rpm to some degree or if monitoring is disabled they spin up full speed. The other setting such as silent or the rpm threshold controls in the bios simply don't do anything there is no circuit to control the speed.

That would be the CPU/CHA FAN PWM pin.
by switching monitoring on, is there any performance impact? noise level, is it acceptable?
 

DavidM012

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Depends entirely on the brand(s) of fan(s) that you have. I have a i series cooler that is like a jet fan on full speed that is a true 4 pin pwm fan and the 3 pin be quiet! pure wings do something weird and spin up faster and a bit louder on the cpu header than the cha fan header when the bios setting is exactly the same, where the artic f12 silents I have that are a comparitively weaker airflow at full speed on the cpu header, remain silent.

Basically the thing to look for on the tech spec sheet when buying fans is the db(a) and cfm, along with mtbf (mean time between failure) and rpm.

Somewhere in the balance of those specs. vs price is value for money. For quiet operation stay below 20dba. That means buy fans that claim to be 20dba or less.

Generic unbranded fans are louder due to greater air turbulence or bearings that vibrate. Air turbulence depends on the shape of the fins as well.

Some fans get around the noise issue by being larger 140mm's with a lower rpm and airflow, that is stil equal to or greater than many of the ultra cheap 120mms, but quieter.
 
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Yes 3pins work on the 4 pin header but don't have the sense wire I think so there isn't as much speed control. All my fans are 3 pins on 4 pin headers and all I can do to control the speed is switch on monitoring in the bios which seems to cut the rpm to some degree or if monitoring is disabled they spin up full speed. The other setting such as silent or the rpm threshold controls in the bios simply don't do anything there is no circuit to control the speed.

That would be the CPU/CHA FAN PWM pin.
3pin fans do have RPM sense wire/connector, its PWM (Pulse With Modulation) that's missing. If plugged in 4 pin (PWM) header, BIOS has to be set to voltage control.
 

Karadjgne

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3 pin fans have 3 wires. Hot, ground, tach. Being DC, they are controlled by the voltage on the hot, which is generally 5v low or 7v low and 12v high, depending on the fan. This sets up your duty cycle. So a 1000rpm fan with 5v low (40% duty cycle) will spin at 400rpm - 1000rpm. A 7v low (60% duty cycle) will be 600 - 1000rpm. That same fan at a 2000rpm max would be 800rom or 1200rpm lows.

4 pin fans have 4 wires. Hot, ground, tach, pwm signal. Because they are pulse modulated the hot wire will always supply a full 12vDC. This means that the fan can go much lower duty cycle since it's getting 12v. Generally you'll see lows as low as @ 20%. The pulse is like Morse code, literally tells the fan motor off/on. Fans don't instantly spin at maximum speeds, it takes a second while they wind up, so if during that windup, pulse says off, it stops voltage to the fan motor. Which starts to slow. Then pulse says on, starts to wind up again etc. This has the effect of making that fan always in a state of trying to reach full speed, but never gets there. The timing and length of on/off pulses is what sets the rpm of the fan ± a few.

The motherboard header has 4 pins. Hot, ground, tach, pwm. For a DC fan, means just using the first 3 pins, and the connector/header are keyed, so will only fit the first 3. By putting the bios on DC mode, you tell the header it has to regulate voltages and can ignore making a pwm signal. If you put the bios on pwm mode, it tells the header to supply constant 12vDC and use the pwm pin.

With AIO's, you can set the bios either way. Doesn't affect the pump, since the cpu_fan header is seperate, it's dedicated pwm. Pumps are 3 wire so will always get a constant 12v from a 4 pin cpu_fan header.

As far as duty cycle goes, that relies on the fan. A 7v low Arctic at 1000rpm max is going to see 600-1000rpm ±, whereas a 5v low generic case fan with a 2000rpm max will see 500-2000rpm ±. If you set both to 70% duty cycle, the Arctic will be at 700rpm, the generic at 1400rpm. Considerably different speeds and volume output.
 
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Paperdoc

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First, let's keep the uses of the mobo fan headers clear. That mobo has one CPU_FAN header, two for water pumps (one designated for AIO systems like you have, and another for other pumps) and two CHA_FAN headers. In general, the CPU_FAN header can ONLY use the temperature sensor inside the CPU chip to guide its automatic control of its fan, and that makes sense because its ONLY function is to cool that chip. Very often the two pump headers also are restricted to using that sensor. On the other hand, the normal configuration of the two CHA_FAN header is to use a different sensor for guidance - one on the mobo - since these are intended for case ventilation general use, and NOT for cooling the CPU. So it is these CHA_FAN headers you should be using for your case fans.

Note that by design, you can always plug a 3-pin fan female connector into a 4-pin header, and there's only one way to do that.

Next, as you say, all your mobo headers have 4 pins. But that does NOT tell what you want to know. Both 3-pin and 4-pin fans CAN have their speeds controlled automatically by a mobo header, BUT the method they require is different. A 3-pin fan's speed can ONLY be controlled if the header uses the older method, Voltage Control Mode (aka DC Mode). Look in your mobo manual on p. 3-7 where it outlines options available for the several headers. For EACH of your two CHA_FAN headers that you will use for the 3-pin case fans, you need to select that header on the left, and then at upper right set it to DC Mode. IF you decide to set up a custom fan curve rather than use the pre-set Standard curve (see p. 3-8) you can do that, too. Remember to SAVE your settings as you exit.

Your cooler Master ML360R AIO system comes with thorough instructions on the details of how to connect it, and includes a Splitter to do that. The PUMP unit must plug into a pump header, and I suggest the mobo's AIO_PUMP header for that. Then you use the included Splitter to connect all three rad fans to the CPU_FAN header so it can control those fans and thus the CPU temperature. There is an additional system with cables and a Controller box for the ARGB lights in each of the rad fans. You will need this because the fans contain the more advanced Addressable RGB lighting system which your mobo cannot handle. However, the Corsair SP120 RGB fans in the case are of the simpler plain RGB type, and your mobo DOES have one header of that type (see manual p. 1-10) you can use to power and control those case fan lights. If you need help with either lighting system, post back here.
 
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Solution

hich96

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May 10, 2019
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Sorry for the late response, i just ended the build, it was a big mess xD, corsair crystal 460x case is really a big puzzle to solve when it comes to cable management,
going back to subject, as all of you said, i have set custom fan curves for every and each fan including the aio pump which was runnig almost at 100% full time, which always caused some undesirable noises, after tunning and setting those curves everything works great and quiet, im pretty impressed with the noise level which are amazingly low, did some stress testing and the temps were under 75c most of the time under full load 100% with the cpu being overclocked to 4.9ghz 1.35v
Thanks for every single one of you chaps, really good advices