Three Pin Fan Control Help

[stribyp]

So I am building my first pc and I am getting a couple of Cooler Master R4-S4S-10AK-GP 60.9 CFM 140mm Fans to compliment the two Fractal Design Dynamic GP14 140mm fans that come with my case. All of these are 3 pin fans. Using the ASRock AB350 Pro4 ATX AM4 Motherboard, is there a way to control these fans through the bios or any a other way?

 

[Paperdoc]

You should have no problem. There are a couple of points to atttention to.

1. Your mobo has three CHA_FAN headers, each with 4 pins. The specs for header 1 are not clear. But CHA_FAN2 and 3 both say they will auto-detect whether you have connected 3-pin or 4-pin fans, and adjust accordingly. So use only those two headers for your fans.

2. Any such fan header can supply up to 1.0 amps total to all its fans. The Fractal design units say they pull 0.2 amps max each, and the Cooler Mater ones are less than 0.1 amps each. So connecting two of any of those fans together on one header is no problem.

3. To do that, you will need two SPLITTERS, like this:

https://www.newegg.com/Product/Product.aspx?Item=N82E16812423160&cm_re=coboc_fan_splitter-_-12-423-160-_-Product

These are 4-pin splitters, but they work perfectly for 3-pin fans, too. Each of these will let you connect two fans to a single header.

4. That is an example of a SPLITTER. It has one input arm with a connector to plug into a mobo fan header, and two (some have three) output arms that have connectors for your fans. Do NOT buy a HUB. That type of device can look like this, but it also has a third arm type that must plug into a power output connector from the PSU. A Hub can only work with 4-pin fan systems, so that's not for you.

5. You should be aware that any device tlike thiese splitters will send to the mobo header for display the speed signal of only ONE of its fans; the other will be ignored. This has no impact on speed control - it only means you can't "see" the speed readout for some of your fans.

 

[stribyp]

Thanks so much! If I use a 4 pin splitter and plug 3 pin fans into it, will the motherboard read them as a 4 pin (since the splitter is 4 pin and physically plugged into the mobile) or as 3 pin? I'm just not sure whether I should get 3 pin splitters or 4 pin splitters. @Paperdoc

 

[Paperdoc]

First, thanks for Best Solution.

The splitter design has nothing to do with the logic work. A Splitter only makes connections from mobo header to fan.

First, the signals involved. In both systems, Pin #1 is Ground (Black on a 3-pin fan), Pin #2 is the +VDC supply, and Pin #3 carries a speed signal (2 pulses per revolution), generated by the fan motor, back to the mobo for counting to measure speed. 4-pin fan systems change the signal on Pin #2 to a fixed +12 VDC, and then add the PWM signal on the new Pin #4. (4-pin fans tend to use different color codes on their wires, but the functions of the first three are almost the same.) Inside the fan there is a small chip that uses the PWM signal to modify the flow of current from the +12 VDC supply line through the motor windings, thus altering its speed.

The difference in design between 3-pin and 4-pin fans is in the method of controlling the fan's speed. For 3-pin fans, the header sends out a voltage to the motor which ranges from 12 VDC (full speed) to about 5 VDC (less might cause the fan motor to stall). That method is called Voltage Control Mode, or DC Mode. A 4-pin fan header that actually uses the new PWM Mode sends +12 VDC to the fan on Pin #2 at all times, and also sends the PWM signal for the fan's chip to use for control.

If you use a 4-pin Splitter and a 3-pin fan, the fans simply will never "see" the signal on Pin #4, which it cannot use anyway. But if the header only sends out a fixed +12 VDC on Pin #2 (as in PWM Mode) the fan will always run full speed. An auto-sensing system should find a way to determine which fan type is connected and change to Voltage Control Mode if necessary. One way I can imagine is easy at start-up each time. Send out the signals in PMW Mode and change the PWM signal to alter fan speed, then check what the speed signal does. If it does not decrease, change to Voltage Control Mode and verify that is working.

There is another slightly deceptive way this can be done. Many mobo makers use only 4-pin headers, but actually operate them as 3-pin headers using Voltage Control Mode only (they never even try PWM Mode). This works perfectly for 3-pin fans, of course. But the design of the new 4-pin fans has backwards compatibility this way. If it receives only the 3-pin signal type, it gets no PWM signal at all and cannot use that to change the current from through the motor. But the Voltage supplied on Pin #2 is NOT fixed as a PWM system would. It is varying, so that controls the motor speed and the mobo header appears to have full control of either type of fan. There is one small thing that can cause trouble with these systems: if you use a Splitter to connect several fans of DIFFERENT types to the same header, some of them will not perform properly.

So much for the whys and hows. That is why I said it does not matter which type of Splitter you use. No matter which way the "auto-sensing" header is doing things, it will be able to control your 3-pin fans.

 

[stribyp]

First, thanks for Best Solution.

The splitter design has nothing to do with the logic work. A Splitter only makes connections from mobo header to fan.

First, the signals involved. In both systems, Pin #1 is Ground (Black on a 3-pin fan), Pin #2 is the +VDC supply, and Pin #3 carries a speed signal (2 pulses per revolution), generated by the fan motor, back to the mobo for counting to measure speed. 4-pin fan systems change the signal on Pin #2 to a fixed +12 VDC, and then add the PWM signal on the new Pin #4. (4-pin fans tend to use different color codes on their wires, but the functions of the first three are almost the same.) Inside the fan there is a small chip that uses the PWM signal to modify the flow of current from the +12 VDC supply line through the motor windings, thus altering its speed.

The difference in design between 3-pin and 4-pin fans is in the method of controlling the fan's speed. For 3-pin fans, the header sends out a voltage to the motor which ranges from 12 VDC (full speed) to about 5 VDC (less might cause the fan motor to stall). That method is called Voltage Control Mode, or DC Mode. A 4-pin fan header that actually uses the new PWM Mode sends +12 VDC to the fan on Pin #2 at all times, and also sends the PWM signal for the fan's chip to use for control.

If you use a 4-pin Splitter and a 3-pin fan, the fans simply will never "see" the signal on Pin #4, which it cannot use anyway. But if the header only sends out a fixed +12 VDC on Pin #2 (as in PWM Mode) the fan will always run full speed. An auto-sensing system should find a way to determine which fan type is connected and change to Voltage Control Mode if necessary. One way I can imagine is easy at start-up each time. Send out the signals in PMW Mode and change the PWM signal to alter fan speed, then check what the speed signal does. If it does not decrease, change to Voltage Control Mode and verify that is working.

There is another slightly deceptive way this can be done. Many mobo makers use only 4-pin headers, but actually operate them as 3-pin headers using Voltage Control Mode only (they never even try PWM Mode). This works perfectly for 3-pin fans, of course. But the design of the new 4-pin fans has backwards compatibility this way. If it receives only the 3-pin signal type, it gets no PWM signal at all and cannot use that to change the current from through the motor. But the Voltage supplied on Pin #2 is NOT fixed as a PWM system would. It is varying, so that controls the motor speed and the mobo header appears to have full control of either type of fan. There is one small thing that can cause trouble with these systems: if you use a Splitter to connect several fans of DIFFERENT types to the same header, some of them will not perform properly.

So much for the whys and hows. That is why I said it does not matter which type of Splitter you use. No matter which way the "auto-sensing" header is doing things, it will be able to control your 3-pin fans.

Thank you so much for the help!