[SOLVED] Can i connect one 4 pin fan and one 3 pin fan into a 4 pin motherboard header with a Y cable?

[GuiLLeBu]

So that's the question. My motherboard only have one fan header, and i have a 4 pin fan and a 3 pin fan, so can i connect those 2 different types of fans through the 4 pin motherboard header using a Y cable? Could the motherboard still control the fan's speed of the 4 pin fan without affecting the 3 pin fan?

My motherboard is a GIGABYTE B450 S2H

 

[justin.m.beauvais]

In theory, yes. In practice, I'm not totally sure. It shouldn't hurt anything to try.

 

[OllympianGamer]

No both fans will run at the same speed. You will need to buy a fan hub if you want control over more than 1 fan.

 

[GuiLLeBu]

No both fans will run at the same speed. You will need to buy a fan hub if you want control over more than 1 fan.

So the 4 pin fan would work as a 3 pin fan right?

 

[OllympianGamer]

So the 4 pin fan would work as a 3 pin fan right?

If the y splitter was 4 pin I assume so, but both fans would always run at the same rpm.

 

[Paperdoc]

YES, you can do this. You need to understand a few details, but it will work just fine.

1. A mobo fan header can only deal with the speed signal coming back to it from ONE fan. So, when you use s Splitter or Hub to connect more than one fan to a signle header, the splitter (or hub) will onlky send back the speeed form one fan, and ignore the other. You will never "see" the speed of the second fan anywhere, but this has NO impact on ability to control the fan speed.
2. The second function of a fan header is to monitor the speed signal of its fan for FAILURE and warn you about that. When you use a Splitter (or Hub) there is no way to monitor the speed of the UNreported fan, so you should check yourself for time to time that they all still are working.
3. The METHOD of control of a fan speed is different for 3- and 4-pin fans, so mixing them together on a single header can cause some odd behaviour. In the fan header configuration, this is the item called the MODE of control. Choices normally are Voltage Control Mode (aka DC Mode), PWM Mode or Automatic (makes it own choice). The ONLY way to control the speed of a 3-pin fan is to use the DC (Voltage) Mode. If you try to use PWM Mode with a 3-pin fan, it always will run full speed, even if the 4-pin fans' speed IS under control. BUT, a 4pin fan CAN have its speed controlled by that DC Mode. So for your situation of mixed fans on one header, configure it to use DC Mode, and that can control BOTH fans.
4. You do NOT need a fan HUB, which is a different device from a Splitter. A Splitter has connections only to the mobo fan header and the fans. A Hub also has an additional connection arm that gets power from an output from the PSU. A Hub can NOT control the speed of a 3-pin fans, so do not use one.

 

[Paperdoc]

Thanks for Best Answer.

 

[Karadjgne]

Just one addition, maybe, and thats fan duty cycles. Because of the way pwm fans work, they are far more efficient, but only when at 12v. At lower voltages, their smaller motors can be strained vs a regular 3pin DC fan. So I would use the pwm fan on the 4wire side of the splitter and the 3pin fan on the other. This will prevent the pwm fan from going below its voltage duty cycle and stopping entirely.

 

[Paperdoc]

I disagree with Karadjne on a couple of points. I have NO disagreement on the comments about efficiency of the fans and ideal voltages, etc.

OP's situation is how to power AND control a 3-pin and a 4-pin fan from only one SYS_FAN header. A Splitter certainly is the way to make that connection. But that means that BOTH of these fans will receive the SAME signals, depending on which way the SYS_FAN header is configured. If it its set to use PWM Mode, then the 4-pin fan's speed will be controlled in the ideal manner. BUT the 3-pin fan will have NO control of its speed, because the power provided from header Pin #2 is always 12 VDC. The 3-pin one will always run full speed.

If the header is configured for Voltage Control Mode, the 3-pin fan's speed WILL be controlled properly as the voltage supplied from Pin #2 varies. For the 4-pin fan, although this method is not technically as good as using PWM Mode, it WILL achieve speed control of it, too. That is why I recommended using Voltage Control Mode.

It is true that, of the two output male connectors on a typical Splitter, one has all four pins and the other is missing one pin. BUT that missing one is Pin #3. The function of that pin to to take the fan's speed signal back to the mobo. Now, a mobo header can only deal with ONE fan's speed signal, so NOT having Pin #3 in the second output connector merely ensures that the speed signal from that second fan is NOT sent to the mobo. This has NOTHING to do with suppling the PWM signal from the mobo header to the fans, because that is done with Pin #4.

 

[Karadjgne]

I think you mistake what I'm saying, or trying to say. The motors on a DC fan are slightly more robust than on a pwm fan. As a result, DC fans can handle lower voltages better. Most DC fans will drop to 40% or 60% (5v or 7v), whereas pwm fans can have issues at 5v and/or 7v, many pwm won't spin at lower than 9v. (ish)

If you use the DC fan as primary, on the 4pin, it'll read that fan through the tach, so may take the fan down as low as 5v at idle. If the pwm fan on the slave is dropped to a corresponding 5v, it may stop altogether and be constantly trying to start, which can possibly cause damage to the motor as it has volts/amps applied to a single area on the rotor, possibly for hours.

If you use the pwm as primary, it'll only drop as low as the fan can reasonably handle, without tripping any low rpm warnings or stopping.

Control the weakest fan, not the strongest. Control will still be in voltage mode, not pwm, regardless of which fan is primary and slave.

 

[Paperdoc]

OK, I get that now. So OP should use Voltage Control Mode, but ensure that the fan connected to the Splitter output with all four pins is the PWM (4-pin) fan. That fan is the more likely item to experience stalling, and connecting this way will ensure any such problem is detected and automatically fixed right away.

 

[Karadjgne]

Exactly. With pwm as slave, it can stop, totally undetected, making it totally useless