AMD cooling fan - why the third wire?

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JohnB

My Athlon cooling fan has been making a lot of noise, so I replaced it with
a generic $5 fan that has only two wires- for +12 VDC and ground. The old
fan had a third wire (blue) and the mobo has three-pin headers for such
fans.

The new fan is delightfully quiet, and the computer seems happy.

I realize there's some kind of temperature read in the bios, but I never
look at that. This computer stays on all the time. I rarely reboot, and
almost never look into the bios.

Can anyone explain what the third wire is for?
Thanks,
John
 
JohnB said:
My Athlon cooling fan has been making a lot of noise, so I replaced
it with a generic $5 fan that has only two wires- for +12 VDC and
ground. The old fan had a third wire (blue) and the mobo has
three-pin headers for such fans.

The new fan is delightfully quiet, and the computer seems happy.

I realize there's some kind of temperature read in the bios, but I
never look at that. This computer stays on all the time. I rarely
reboot, and almost never look into the bios.

Can anyone explain what the third wire is for?
Thanks,
John
Click to expand...

It's used to monitor rotational speed of the fan.
 
JohnB said:
My Athlon cooling fan has been making a lot of noise, so I replaced it with
a generic $5 fan that has only two wires- for +12 VDC and ground. The old
fan had a third wire (blue) and the mobo has three-pin headers for such
fans.

The new fan is delightfully quiet, and the computer seems happy.

I realize there's some kind of temperature read in the bios, but I never
look at that. This computer stays on all the time. I rarely reboot, and
almost never look into the bios.

Can anyone explain what the third wire is for?
Thanks,
John
Click to expand...
It is used to monitor the speed of the fan. Many motherboards will not boot
if it detects that the fan is not spinning or spinning too slowly.
 
JohnB said:
My Athlon cooling fan has been making a lot of noise, so I replaced it with
a generic $5 fan that has only two wires- for +12 VDC and ground. The old
fan had a third wire (blue) and the mobo has three-pin headers for such
fans.
Click to expand...

Speed sensing... Not a big deal if you don't monitor it.

BUT! What kind of CPU do you have? Any $5 heatsink will not be good enough
for todays AMD CPU's!
 
Athlon 1.1 GHz. It's a couple of years old.
I didn't change the heatsink, just the fan. The quietness of the new fan is
"deafening." I love it. The CPU is happy, and I'm happy. To hell with the
third wire, it's not worth some $15 extra to buy the heatsink+fan combo just
to retain a feature I never look at.
 
As I swapped the fan without taking the computer down, your point has been
greatly appreciated. I downed the computer, with new fan in place, and old
fan absent. The computer booted just fine.

Along the way, I looked into the bios screen, and sure enough, the CPU fan
speed now shows a big zero.

Thanks, again!
John
 
Athlon 1.1 GHz. It's a couple of years old.
I didn't change the heatsink, just the fan. The quietness of the new fan is
"deafening." I love it. The CPU is happy, and I'm happy. To hell with the
third wire, it's not worth some $15 extra to buy the heatsink+fan combo just
to retain a feature I never look at.
Click to expand...

Keep an eye on the temperature for the next few days anyways. It's
not just the heat sink that's important, it's the air flow -- that's
why there's a fan. The more air goes through, the more cool air is
brought in across the fins to absorb the heat and remove it.

The cooling efficiency of the cooler may be compromised if the fan
achieves the noise reduction by reducing air flow. If the temperature
increases significantly above what you had before, (like say it goes
into the mid 50C range) I'd suggest you replace the fan with something
that pushes more cubic feet per minute.
 
The cooling efficiency of the cooler may be compromised if the fan
achieves the noise reduction by reducing air flow. If the temperature
increases significantly above what you had before, (like say it goes
into the mid 50C range) I'd suggest you replace the fan with something
that pushes more cubic feet per minute.
Click to expand...

Putting 50C range as the guideline is quite subjective.
Do put into consideration about room temperature (summer time, winter
time etc ...).
 
WebWalker said:
Putting 50C range as the guideline is quite subjective.
Do put into consideration about room temperature (summer time, winter
time etc ...).
Click to expand...

It was based on the default thermal shutdown settings of the last two
motherboards I've owned. Both were set (from the factory) to shut
down at 60C.

===========================
MCheu
 
It was based on the default thermal shutdown settings of the last two
motherboards I've owned. Both were set (from the factory) to shut
down at 60C.
Click to expand...


That sounds too low... IIRC, AMD's guideline is around 80-90C.
Most generic T-Bred systems using the AMD retail HSF run at > 50C all
day, everyday.


Dave
 
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