Andy said:
I got the wrong fan. It is one for cooling the computer chassis instead of the cpu cooling fan.
The new one has a 4 wire connector while the old is 3 wire.
Can I use the new one in place of the 3 wire fan ?
New fan does draws twice the amperage of the old, so I quess it would be louder.
Andy
The alignment tab on a four pin fan, is the same
size as a three pin fan. So that a three pin can be
connected to a four pin motherboard header.
Pin Signal Function
1 GND
2 +12V
3 RPM Fan sends out two pulses per rotation, to the computer
4 PWM Fan accepts 5V level, pulse width modulation for speed control.
Computer sends 25KHz signal, where the pulse width varies with
desired speed setting.
Pin Signal Function
1 GND
2 +12V
3 RPM Fan sends out two pulses per rotation, to the computer
If the PWM pin is left "floating", it is pulled high by the fan.
A permanently high signal on PWM, is like a 25KHz signal where
the "logic 1" width is 100%. The floating pin ends up being a
request for "maximum speed". The 25KHz was chosen, to be out
of the audible human hearing range.
*******
Fans fit roughly into four CFM categories. Low, medium, high, ultra.
I have an ultra here, at around 110CFM and maybe one ampere of current.
A low or medium might be in the 35CFM range, maybe 100-200ma current,
and those are relatively quiet. You can't really sit next to the 110CFM
fan, which is 120mm outside dimensions, and 37.5mm deep. That fan
has to be turned down, to be useful.
A CPU fan doesn't have to be a monster, if the heatsink fins have a
relatively large surface area, and the fin spacing is such that
air moves easily (low arrestance). Then, a lower CFM fan can be used,
or a medium fan can be speed controlled to good effect.
You tell by the CPU temperature, while a 100% loading program
(Prime95) is running, as to whether you got the right fan. By
matching the CFM rating and size dimensions, that should get
you into the right ballpark. If you don't have a CFM to work with,
then current draw will give a rough idea.
The only computer designs that use the ultra idea, are things
like single-fan Dells, where one fan cools the CPU and computer
case. Some of those have a high rating, which under normal
circumstances is never used. The fan in that case, stays turned
down, unless the machine goes nuts. And then the vacuum cleaner
noise of the machine, alerts you a failure is occurring on your
machine.
Paul