MikeB said:
I have an Apevia case that I'm upgrading. The case came with 2 80mm 2-
wire fans (one on the back and one at the top of the case) I added a
3rd one at the front of the case. I ran all these fans off the power
supply cables for the HDD and/or CD/DVD drives.
That meant when the system was suspended, the fans still spun and were
still lighted.
I'm now upgrading my motherboard to an Intel DP35DP.
This board has fan headers on the board that I'd like to use. Some of
the headers are 3-pin and some are 4-pin. I understand that a 3-pin
header can control fan speed. What does a 4-pin header control
additionally?
I'd like to get some cool LED/UV fans that have the right wiring. My
searches aren't exactly turning up a lot of info on the number of
wires a fan has. Does anyone have a good place to shop for fans with
speed control?
Thanks
Two wire fan. The only way to change the speed of this fan, is reduce the
+12V pin, below 12V. Some fans will run at 7V, and some still run at 5V.
If the voltage is too low, the fan may fail to spin, which is why some
fan controllers don't drop the voltage too much.
X X X
+12 GND
This is a three wire fan. The third wire is the RPM signal. It pulses
twice per rotation of the fan (pulse sent from fan to motherboard). A
monitor chip can count the pulses and tell you the speed of the fan.
Speed control remains the same as in the previous case. Reducing the
12V value, makes the fan spin slower.
X X X
RPM +12 GND
This is a four wire fan. The fourth wire (PWM) is a speed control. The signal
on the fourth wire, operates at about 25KHz. The frequency selected, is
supposed to be high enough, to be inaudible. The signal on the fourth wire
is a square wave. The duty cycle of the square wave (high time versus
low time), is what controls the speed. PWM stands for Pulse Width Modulation.
The frequency of the control signal remains constant, but the duty cycle
varies according to what speed the software selects for the fan.
X X X X
PWM RPM +12 GND
On a fan that has the PWM signal, the PWM is what is supposed to be used
to control the speed. The 12V signal stays at 12V, and the PWM varies the
speed. You aren't supposed to drop the voltage feeding a PWM controlled
fan, as that could affect the ability of the MOSFET inside the fan,
from properly controlling it.
As for how the voltage on the 12V pin of a three pin header goes, there
are two methods which are used to change that voltage. It isn't important
which method is used, from an end user perspective.
Not very many three pin fan headers have a speed control feature. Some brands
of motherboards are better than others, at offering the speed control.
Other brands control at most two fans (CPU and one other). Download and read
the user manual before buying, to discover how many speed controlled fans
are offered. If speed control is featured on a board, chances are that
the Speedfan program from Almico.com can be used to control the speed.
On some motherboards, speed control is totally automated, so no software
is needed at the OS level. (The speed control can be done in hardware - some
hardware monitor chips are smart enough to have a Cruise Control feature
for the fan.)
So that is a quick overview of the methods.
With regard to your "suspend" symptoms, the fact that the fans were
still running on your old system, means you were in S1 state. If the
computer had been set up for "suspend to RAM" or S3 state, the fans
stop spinning in that state. Only the RAM remains powered in S3. You
can fix that with a program called "dumppo.exe" from Microsoft, assuming
that in Device Manager, the properties of the "Computer" entry have the
word "ACPI" in the text string.
For case fans, a two wire fan can be controlled just as easily as a
three wire fan. Both fans will use the "drop the 12V level" control
method. The purpose of the third wire, is just for monitoring the
RPMs of the fan. So a two wire fan is good enough, if the motherboard
has speed control on all the fans. The motherboard doesn't need to
know the RPMs, to change the voltage sent on the 12V pin.
You can also use a voltage reducer, inline with the fan cable. This
allows a fixed amount of speed reduction, that does not change with
temperature. The Zalman Fanmate II is an example of a simple
speed reducer, for a 6W or less fan. This would be suitable for a
fan header which offers no speed control. The purpose is to allow
you to make the fan run a bit quieter.
http://www.newegg.com/Product/Product.aspx?Item=N82E16835118217
There are also products that implement fan speed control completely
separately. These can be quite expensive. Here is a typical picture
of one. These things may have multiple temperature sensors, and that
is how the thing figures out how fast to run the fan. What is missing
from this picture, is the mess of wires needed to make it work. When
you use one of these, the inside of your computer case becomes a
"wire jungle".
http://icrontic.com/img/3876
Paul
