I recently built a PC with an ASUS TUF Gaming B650E-E WiFi motherboard, Ryzen 7 7800X3D, Krux Exo case, Endorfy Navis F360 ARGB cooler, and a Krux fan hub powered by SATA. The hub connects to the motherboard through the CHA_FAN header for PWM control. While I'm in the BIOS, the case fans don't spin at their normal setting. If I change CHA_FAN to Full Speed or Maximum, they start spinning immediately. Once I leave the BIOS, they return to their normal speed and work properly. Is this expected behavior, or should I adjust the Q-Fan settings, PWM/DC mode, fan curve, or minimum duty cycle? Could the SATA-powered fan hub be causing this?
2 Answers
ASUS boards can be especially aggressive with their default Q-Fan settings. Some fans won’t start reliably at a very low duty cycle, and a hub can make that more noticeable. Set the CHA_FAN header to PWM mode if the hub and fans support PWM, then create a custom curve with a minimum of roughly 30–40% so the fans receive enough power to keep spinning. The SATA connection only powers the hub; it isn’t inherently a problem.
This is usually normal. While sitting in the BIOS, the system is barely generating heat, so the default fan curve may set the header output extremely low or even to zero. Switching the header to Full Speed bypasses the temperature-based curve and forces the fans to run. Since they work normally after the operating system loads, there probably isn’t a hardware problem with the fans or hub.
So there’s nothing I really need to worry about as long as they work normally once the system boots?
Does that point more toward the motherboard’s fan curve than a fault with the fans themselves?