Your wiring:
4 pin CPU fan header ----------------- 4 pin CPU fan
4 pin CHA_FAN1 header ---------------- 3 pin Tricool 120mm (low, medium, or high)
3 pin PWR_FAN header ----------------- 3 pin Tricool 140mm (low, medium, or high)
In the BIOS, you can set the CPU fan to "controlled" or just run it full speed.
For the CHA_FAN1 BIOS setting, you would disable the speed control, and use
the Tricool switch.
For the PWR_FAN BIOS setting, there isn't any. PWR_FAN just delivers the full
12V to the fan. The Tricool Low, Medium, or High switch, sets the final voltage
delivered to the fan.
*******
By turning off the CHA_FAN1 fan speed controls, the CHA_FAN1 runs at
a constant full speed. What that means is, the 12V pin delivers the full
12V. The PWM signal is an output from the motherboard to the fan, but
because you're plugging a 3 pin fan into a 4 pin header, the PWM signal
doesn't get connected. Since the fan is not a PWM type, it isn't possible
to control it from the Asus BIOS.
Fan headers have at least two control methods. You can vary the 12V delivered
on the motherboard, to the 12V pin on the fan header. That is the old way to
do it. Or, you can deliver a full 12V to the fan header, and send the control
signal "PWM" to the fan, to tell it what speed to run at. Using "Pulse Width
Modulation", makes it easy for a single transistor inside a PWM fan, to control
the resulting voltage delivered to the fan motor. The header is four pins
in that case - 12V, GND, RPM, PWM. RPM monitors the speed. PWM controls the
speed.
Since it is relatively cheap to provide PWM fan control, expect to see it more
and more on motherboards. The voltage control method, probably costs $1 per
fan header. Obviously, the PWM method only works with PWM fans, so being
a cheap solution, not every user will be happy.
Asus is never very generous with fan control. There are three levels from
a marketing position.
Non-Qfan boards have no fan control. All headers deliver
full 12V. The Tricool switch is the one to use with them, to set the speed.
Q-Fan boards, only control the CPU_FAN header. In the old days, they provided
a 3 pin connector, and varied the 12V delivered. A BIOS control would exist
for setting when to change the speed.
The motherboards with "Q-Fan2" have two fan headers controlled. In the old days,
that would be two three-pin headers with voltage control.
Your board provides two controlled headers (which would make it Q-fan2 as far
as the marketing people are concerned). But it uses the cheaper to make, PWM
method. Your three pin fan, can't be controlled by the PWM signal, so the BIOS
speed control on your CHA_FAN1 is useless. Leave the speed controlling feature
turned off. The motherboard will think it is running full speed. You can use
the Tricool switch to set the basic speed.
The PWR_FAN header is a "dumb" header, so always delivers the full 12V. The
Tricool fan switch will help you with speed control there.
Is there a "decision tree" or "flow chart" for fans ? Yes, but it is complicated
and it is easy to make mistakes. There are just two many combinations (old and
new motherboard types) to make this easy. Some motherboards have both voltage
control and PWM methods available, for example, on the same header. Lots
of permutations and combinations.
*******
A couple years ago, the only PWM fans you could buy for case cooling, were
from Rexusa. Newegg used to carry those. A PWM fan has four pins, so includes
the PWM signal. I notice now, on Newegg, there are a lot more PWM fans.
http://www.newegg.com/Product/Product.aspx?Item=N82E16835706032
Now, that one is a monster. 150.33 CFM, 56.4 dBA noise. The neighbors will
hear that, next door. That needs speed control in the worst way. You could
connect that to your CHA_FAN1 header, then turn on the BIOS speed control,
to keep that fan from howling. They use fans like that, to cool Dell
computers (i.e. one fan to cool everything, including CPU). That is the
kind of fan you use, to make a "Dell vacuum cleaner".
That fan draws 1.74 amps flat out, so could potentially burn a fan header
that doesn't have a current rating that high.
This one is a bit more discrete and won't wake the neighbors. It is PWM
and has a four pin connector on the end. You could leave this running
full speed and you probably couldn't hear it (compared to, say, your
video card fan). This would go to your CHA_FAN1 header.
http://www.newegg.com/Product/Product.aspx?Item=N82E16835214003
You can see the four pin connector on the end, confirming it has a
PWM control signal.
http://images17.newegg.com/is/image/newegg/35-214-003-S03?$S640W$
Regular chassis fans might have a three pin connector, and two or
three wires. A three wire fan supports RPM measurement via the
"RPM" signal. A chassis fan with two wires, is completely dumb
and can't be monitored. (Well, it can, but that is a story for
another time.)
Paul
