Concept Fan silencer module

VELKASE Michael

King of Cable Management
Original poster
VELKASE
Gold Supporter
Oct 7, 2018
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I've been thinking about developing a device that would completely silence fans by turning them off when the computer is idle. This would allow the components to be cooled actively when they are under load and passively while idle, and would be useful mostly in larger systems around 7 L in volume or above.

The following is based on my understanding, which may not be entirely correct. If something is incorrect, please let me know.
-12V DC fans cannot be completely turned off via any motherboard BIOS nor software. If the motherboard allows you to send a low voltage to DC fans (below 5V), the fan will either stall or continue operating at a low speed.
-Only some motherboards can stop some PWM fans. Some motherboards may not allow you to send a "0% duty cycle" and limit the minimum to something like 20%. If a motherboard does allow a "0% duty cycle", it's up to the fan manufacturer to decide whether it stops or continues operation at low speed.

The features that it would have are described below and I already know how to implement them, but would love to hear your thoughts on whether something like this would be useful in the first place. What other capabilities would you like something like this to have?

-Have a physical switch to change it between "DC mode" and "PWM mode", corresponding to the type of input the attached fan uses
-In DC mode, if the fan receives less than a certain voltage from the motherboard, turn off the fan.
-In PWM mode, if the fan receives less than a certain % duty cycle from the motherboard, turn off the fan.
-Two knobs that adjust the minimum cutoff for DC and PWM mode to maximize compatibility with different motherboards and motors

Such a device, if created, would probably be made on a small PCB during production. It could plug in between a motherboard's 3/4 pin fan header and a fan's 3/4 pin header.
 

BrickChris

Chassis Packer
Dec 28, 2018
16
4
Mabe a z-diode will work on the positive cable of the fan. This diode lets voltage pass through above a particular voltage.
 

VELKASE Michael

King of Cable Management
Original poster
VELKASE
Gold Supporter
Oct 7, 2018
688
846
Mabe a z-diode will work on the positive cable of the fan. This diode lets voltage pass through above a particular voltage.

This would work for variable voltage controlled fans but not PWM controlled fans. For PWM fans, I think it would need to be filtered and input into a MOSFET used as a switch.