I'm trying to figure out how to connect the 4-pin molex from my case to the 4-pin sys_fan header on my motherboard. I have three 3-pin fans, and they are connected to a small PCB. Here's a couple of images for reference:
- PCB Image 1: https://imgbox.com/9adG5wpK
- PCB Image 2: https://imgbox.com/NWU1kP3a
Is there a way to connect the molex directly to my sys_fan header? I've had a tough time finding an adapter—most are 4-pin molex to 3-pin sys_fan. If I use such an adapter, will my motherboard still control the fan speeds? I thought that some 3-pin fans could be controlled by voltage, not PWM. Any guidance would be appreciated!
2 Answers
Those 3-pin fans are standard DC connectors, so they do allow limited speed control through voltage adjustments. However, that hub you have is supplying a constant 12V, running the fans at full speed. If you want your motherboard to control them, just plug the fans directly into the motherboard's fan headers. The 4-pin headers can handle both 3-pin and 4-pin fans. If you're worried about space, grab a fan splitter cable—either a 3-pin or 4-pin variant works just fine. No need for any special controller!
The molex provides power to that hub, which doesn't seem to send a speed reference back to the motherboard. You might want to consider picking up a fan controller that plugs directly into your motherboard for about $10. Look for one that specifically supports voltage control since you’re using 3-pin fans. I have a 4-pin one for mine, but these controllers can help manage your fan speeds without relying on the motherboard too much. Just a heads up—there are some budget 3-pin controllers available that allow you to switch between low, medium, and high speeds without reading the fan speed from the motherboard.
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