ok question: does my cpu fan header on my A7N8X-Deluxe control the fan by voltage or by the speed of the fan? request: what i am looking to do is, use the onboard temp diode to control the speed of my fans that i will be using to blow on my radiator. i know that i cant hook 2 120mm fans up to the mother board without frying it. what i would like to do is, build a circuit that can "sense" what the cpu fan header but instead of using power from the motherboard use it from the power supply. does this sound like a good idea? will it work? how else could i do this without having to manually control the fan speed? thanks for your time.
It's a PWM signal. It monitors speed via the RPM wire (the middle wire IIRC) and adjusts the frequency of the PWM signal to drive the fan at the correct speed. Your idea could work - I'd probably just try attaching a mosfet to the PWM output off of the mobo. good luck!
Re: Re: motherboard fan headers Correct, but it's very often finally smoothed to rough DC, so the speed wire will work. YMMV.
Re: Re: Re: motherboard fan headers Why would the speed wire work? I always thought that that was how the fan reported back it's speed - not the other way around.
If there's zero voltage to the fan (like in the "off" part of a PWM cycle) there's no power to the fan electronics to produce an accurate speed signal. The mobo PWM reacts to mobo sensor temperature only to vary the fan %on time, the actual fan speed is for information only, not part of the control loop.
Oh I see what you were saying - I thought you were saying that you could run some fans off of the speed wire. Crazy limeys... with your accents and your tea and biscuits.
