Is it ok to stack 2 fans on one system fan connector on the motherboard
- Thread starter Triflexer
- Start date
- Nov 18, 2008
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Most mobo fan ports can supply power to two fans using a splitter, but probably not more than 2 per port.
A 3-pin fan plugged into a 4-pin port will always run full speed. There is no simple conversion for that. However, just in case ... Check the details of your mobo in its manual, and in BIOS Setup. SOME mobos make SOME of their 4-pin ports adjustable to become 3-pin ports if you want to. More commonly this is done only for the CPU_FAN port, but sometimes also for some SYS_FAN or CHA_FAN ports. If your mobo does not have that feature on any of its case fan ports, you get to choose: either let it run full speed or buy a new 4-pin fan.
A 3-pin fan plugged into a 4-pin port will always run full speed. There is no simple conversion for that. However, just in case ... Check the details of your mobo in its manual, and in BIOS Setup. SOME mobos make SOME of their 4-pin ports adjustable to become 3-pin ports if you want to. More commonly this is done only for the CPU_FAN port, but sometimes also for some SYS_FAN or CHA_FAN ports. If your mobo does not have that feature on any of its case fan ports, you get to choose: either let it run full speed or buy a new 4-pin fan.
So the fan port for my mobo has 4 pins, but it looks like it fits the 3 pin connector rather than the 4 pin connector (very thin rectangular prism prongs). Is that maybe what a 3 pin connector looks like. I looked in the manuals and the pins are named "ground, speed control, sense, and nc" I'm thinking I might have to use all the prongs except nc
Post here what is your mobo exactly - maker and model no, with any extra bits like "MAX" or "V1.31", etc. I'd really like to check the manual to be sure the following is correct.
When 4-pin fans were introduced they ensured as much backwards compatibility as they could with existing 3-pin systems. 3-pin fan male ports on the mob have a plastic tongue sticking up beside the pins. The female connector on the end of the fan's wires has a groove on one side to match that tongue, so you can only plug it in one way. A 4-pin connector system was designed to be almost exactly the same as the 3-pin, but with one extra pin and hole added on the end. The mechanical design is almost the same, and the electrical signals on the first three pins also are the same with one small exception. Thus, you CAN plug a 3-pin fan into a 4-pin port, or a 4-pin fan into a 3-pin port, and they will still work.
Well, almost - there is one combination that works with limits. The electrical difference between the two systems starts with the voltage on Pin #2. In a 3-pin (Voltage Control) system, the voltage on Pin #2 is changed by the mobo automatic control system in the range from 0 to 12 VDC, thus altering the fan's speed. In a 4-pin (PWM) system, that voltage on Pin #2 is always at +12VDC, and then a fourth signal (PWM) is supplied to the motor on Pin #4. Inside the motor case is a small chip that uses the PWM signal to control just how much of the time that +12VDC is actually allowed to flow through the motor, and that is how this system alters the motor speed. So, if you plug a 4-pin fan into a 3-pin port, the fan motor gets no PWM signal so it cannot alter the motor speed that way. However, its voltage being supplied on Pin #2 is already being altered by the mobo, and THAT does achieve control of fan speed. BUT if you mis-match the other way (3-pin fan plugged into a 4-pin port), the 3-pin fan gets a constant 12 VDC on Pin #2 and it does not receive (nor could it use, anyway!) the PWM signal, so its speed is always full speed.
Now, you said something very intriguing: "I looked in the manuals and the pins are named "ground, speed control, sense, and nc". I understand there are some mobos out there that use what I might call "fake 4-pin ports". They have 4 pins. But electrically the first three are EXACTLY the same as a standard 3-pin port (including voltage on Pin #2 that varies), and there actually in NO PWM signal being sent out on Pin #4. That sounds exactly like the labels you say the manual shows. Now consider what this does for an attached fan. If it's 3-pin, the fan is connected to a standard 3-pin fan port in terms of its electrical signals, and it works perfectly. If your fan is 4-pin, the design is taking advantage of the backwards compatibility feature of 4-pin fans - it WILL operate well and its speed WILL be controlled by the mobo port. So such a "fake 4-pin port" acts like a "universal" port that can control either type of fan. The only downside to this is that the reason for 4-pin fans in the first place is that they have better low-speed performance and can be started up with lower speed settings, but both those advantages are lost if you plug it into a 3-pin port.
So, IF I understand your mobo correctly, you can plug either 3-pin or 4-pin fans into that one port that has 4 pins (but uses only three) and they will work, including control of speed by the mobo. Yes, you can use a Y-splitter to connect 2 fans to this port. Since it appears the port really is a true 3-pin port anyway, you could use a standard 3-pin Y-splitter for this.
When 4-pin fans were introduced they ensured as much backwards compatibility as they could with existing 3-pin systems. 3-pin fan male ports on the mob have a plastic tongue sticking up beside the pins. The female connector on the end of the fan's wires has a groove on one side to match that tongue, so you can only plug it in one way. A 4-pin connector system was designed to be almost exactly the same as the 3-pin, but with one extra pin and hole added on the end. The mechanical design is almost the same, and the electrical signals on the first three pins also are the same with one small exception. Thus, you CAN plug a 3-pin fan into a 4-pin port, or a 4-pin fan into a 3-pin port, and they will still work.
Well, almost - there is one combination that works with limits. The electrical difference between the two systems starts with the voltage on Pin #2. In a 3-pin (Voltage Control) system, the voltage on Pin #2 is changed by the mobo automatic control system in the range from 0 to 12 VDC, thus altering the fan's speed. In a 4-pin (PWM) system, that voltage on Pin #2 is always at +12VDC, and then a fourth signal (PWM) is supplied to the motor on Pin #4. Inside the motor case is a small chip that uses the PWM signal to control just how much of the time that +12VDC is actually allowed to flow through the motor, and that is how this system alters the motor speed. So, if you plug a 4-pin fan into a 3-pin port, the fan motor gets no PWM signal so it cannot alter the motor speed that way. However, its voltage being supplied on Pin #2 is already being altered by the mobo, and THAT does achieve control of fan speed. BUT if you mis-match the other way (3-pin fan plugged into a 4-pin port), the 3-pin fan gets a constant 12 VDC on Pin #2 and it does not receive (nor could it use, anyway!) the PWM signal, so its speed is always full speed.
Now, you said something very intriguing: "I looked in the manuals and the pins are named "ground, speed control, sense, and nc". I understand there are some mobos out there that use what I might call "fake 4-pin ports". They have 4 pins. But electrically the first three are EXACTLY the same as a standard 3-pin port (including voltage on Pin #2 that varies), and there actually in NO PWM signal being sent out on Pin #4. That sounds exactly like the labels you say the manual shows. Now consider what this does for an attached fan. If it's 3-pin, the fan is connected to a standard 3-pin fan port in terms of its electrical signals, and it works perfectly. If your fan is 4-pin, the design is taking advantage of the backwards compatibility feature of 4-pin fans - it WILL operate well and its speed WILL be controlled by the mobo port. So such a "fake 4-pin port" acts like a "universal" port that can control either type of fan. The only downside to this is that the reason for 4-pin fans in the first place is that they have better low-speed performance and can be started up with lower speed settings, but both those advantages are lost if you plug it into a 3-pin port.
So, IF I understand your mobo correctly, you can plug either 3-pin or 4-pin fans into that one port that has 4 pins (but uses only three) and they will work, including control of speed by the mobo. Yes, you can use a Y-splitter to connect 2 fans to this port. Since it appears the port really is a true 3-pin port anyway, you could use a standard 3-pin Y-splitter for this.
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