Question Want to mod a cheap fan controller

Mar 4, 2021
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Hey there,

As the title suggests, I want to mod a cheap fan controller that runs only on molex and uses a remote control to change between two fan speeds. What I want to do is have the controller draw power from the psu (through molex) and use my motherboards 3 pin voltage control to automatically control the speed.

Sorry if this a dumb question, I'm new to this kind of stuff. Thanks!
 

Lutfij

Titan
Moderator
Welcome to the forums, newcomer!

I think you're better off getting silent PWM fans and a PWM fan hub and be done with it. Silent fans liek the one's made by Noctua are a good choice. PWM fans that are set to the CPU's fan profile, will only ramp up when necessary. A PWM fan hub means that all fans will ramp up or die down in unison while connecting to one fan header on the motherboard.
 
Mar 4, 2021
2
0
10
0
Welcome to the forums, newcomer!

I think you're better off getting silent PWM fans and a PWM fan hub and be done with it. Silent fans liek the one's made by Noctua are a good choice. PWM fans that are set to the CPU's fan profile, will only ramp up when necessary. A PWM fan hub means that all fans will ramp up or die down in unison while connecting to one fan header on the motherboard.
You're probably right lol, but I kinda want the experience plus moneys pretty tight right now. So, I was wondering if there was any way to do it at home for pretty much nothing. At the end of the day, it doesn't really matter because this would be solving a minor annoyance. Thanks for the suggestion anyways tho!
 

jay32267

Illustrious
Hey there,

As the title suggests, I want to mod a cheap fan controller that runs only on molex and uses a remote control to change between two fan speeds. What I want to do is have the controller draw power from the psu (through molex) and use my motherboards 3 pin voltage control to automatically control the speed.

Sorry if this a dumb question, I'm new to this kind of stuff. Thanks!
That might be more tricky than it's worth.
What is the make and model of the controller?
 

Paperdoc

Glorious
Ambassador
You're looking at a complex design project. From what you describe, the cheap controller you have that offers only two speed options VERY likely has inside a VERY simple system that feeds to its fans either full 12 VDC power from the PSU, or a fixed reduced power, probably using a small fast switching circuit to reduce the output for the Low speed.

A voltage-controlled output from a mobo header varies the voltage it puts out on Pin #2 from +12 VDC (full speed) down to about 5 VDC for minimum speed - any lower will allow the fan to stall and not re-start. Basically it consists of a small DC amplifier that turns a control signal into an output voltage, with a maximum output load current of 1.0 A. To duplicate that, you would need to use that voltage signal as input to your own DC amplifier that has similar output characteristics. It is a sort of unity-gain amplifier with a max 12 VDC output voltage capable of at least 1.0 A max at max output voltage. It also would need to be able to tolerate for a few seconds the large current surge demanded by the fan at start-up. Can you design and build such a system?

A signal of this type (Voltage Controlled for 3-pin fans) can also work for the new PWM-controlled 4-pin fans because the new type was designed with this backwards compatibility feature, even though that is not the ideal method of controlling a PWM fan. I suggest that it would be even more difficult for you to try to create a PWM-type controller output starting from an input of the varying voltage signal from a 3-pin fan header.
 

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