[Tfug] 90mm fan

[Adrian]

On Sunday 26 November 2006 22:29, erich wrote:
>     I have a Compaq power supply that's giving out or, more precisely,
> its fan
> is making noises that suggest its days are numbered. Unfortunately this
> fan is 90mm,
> and I had to go out on the internet to get one.
>      This PS has ACPI with thermal sensing that causes the fans to "rev
> up" when the computer
> it powers is "hot on a job". Is there something I missed in the
> specification of the replacement
> fan? I'm wondering if all fans run at variable speed or do you need
> special ones  that
> "rev up" when the power demand rises.
> 

You really need to pull at the existing fan, lookthe part number, and look at 
the number of wires going in... There are basically 3 different types of 
fans, with several variations of each:

1) A "standard" 2-wire static speed fan, say like 12V DC 4500RPM. It may or 
may not be "speed-regulated" by the motherboard/PS by reducing the fan's 
supply voltage, i.e. the PS reduces the supply to 10V so the fan runs quieter 
and only turns at 3000RPM... But either way the fan is the same.

2) A "monitored" 3-wire fan. This is a fan that the motherboard/PS can monitor 
the fan status on. They come in 2 basic types (though there are a number of 
odd, one-off variations): RPM and rotor-lock. RPM is what it sounds like... 
sends out a pulse every nth revolution to indicate it is alive. A rotor-lock 
sends out a high signal constantly (or a low depending on the model) while 
the fan is turning (ie. a "good" signal, not an RPM indication) and the 
reverse when the fan rotor is jambed. Like #1, the speed can be adjusted by 
the system lowering the voltage, but it system does it.

3) A "monitoring" 2 or 3-wire fan. This is a fan that either has a thermal 
sensor built into the frame (typically, though not always 2 wire), or a third 
wire that goes to a special motherboard sensor, and the fan itself 
dynamically adjusts based on the input.

Many of the supposedly "super quiet thermal" fans, that you put in a drive 
bay, or other aftermarket chromed neon blinky waste-o-money things are going 
to be a #3. The typical newer 3-wire processor fans, that plug into the 
motherboard, are #2, nearly always a RPM fan. (You typically find the #2, 
rotor-locked variety in switches/packaged equipment). And most PS supplies I 
have seen use the #1 type.

As to what yours is?... I would guess a simple #2 with sort sort of adjustment 
built into the PS circuitry itself, though you should check the fan model 
number to be sure.


Adrian