Internal PSU fan headers (2/3/4 pins?)

[BadGoldEagle]

Hi

 

Have you ever seen an internal PSU fan with more than three pins?

Most PSUs only have 2 pin fans but I'm wondering if it may be possible to encounter one with a 4 pin connector (ie with separate PWM signal). 

Thanks for your input!

 

 

 

Here's what I'm doing if someone's interested...

I'm modding an ATX PSU and I'll be adding a second fan controller on top of the original one (I need to increase the minimum speed).

Two or three pin fans are controlled using either linear voltage regulation (typically between 6-12V) or with 12V normalized PWM. 4 pin fans also have a dedicated PWM pin but it's not +12V, so you can't plug a 2 pin/3pin fan into a 4 pin header and expect to get the same behavior as with a 4 pin fan.

 

If 4 pin PSU fans do exist, it'll be a real pain to modify my controller to take them into account. The goal here is for that second controller to be compatible will all ATX PSUs, not just one.

[mariushm]

If the fan is 2 or 3 wire, then most likely the power supply adjusts the output voltage going to the fan.

You can read the fan model and check the datasheet for the  rpm vs voltage curve or you could just extract the fan and gradually increase the voltage from something like 6v to 12v and read the rpm as reported by the third wire.

 

As a simple hack you could have a tiny 6-8 pin microcontroller and its ADC pin to measure the voltage sent to the fan and have the microcontroller either output a pwm signal or adjust the output of a voltage regulator.   

 

Probably even simpler could be to use an opamp set to amplify to something like 1.05-1.1x ... so when psu wants to give 6v to fan, the fan will actually get ~6.5v ...

[Applefreak]

I cannot fully answer your question but most PSUs just use a resistor or switch voltage to control fan speed or turning it on or off. I have never seen a 4-pin fan on a power supply, most are 2-pin. 

I am not really sure what you are trying to achieve here but I am guessing you are a professional and know about the dangers of high amp capacitors.