HardwareBanter - View Single Post - power used by just the fan in a power supply?

**Paul[_28_]** · April 7th 19, 02:35 PM posted to alt.comp.hardware.pc-homebuilt

wrote:
I heard at a HPC presentation that the fan in the power supply of a 1U server
"pizza box" can draw 15-20 W! I looked up the specs of some 40 mm case fans used
to cool CPU, DIMMs etc and they were in the range 4 W to 13 W. So I suppose
15 W is plausible.
On the other hand, the larger case fans in a desktop PC need only 1 to 2 W.
So would it be reasonable to assume that in a desktop power supply, the fan
is roughly 2 W draw also?

It should have the power rating printed on the hub.

My Vantec Stealth in the kitchen says 1.2W on it.
12V @ 0.1A. That's roughly the class of fan inside
an average power supply.

Older power supplies were more inefficient, and
there could even be a couple hundred watts of heat
in those, and a faster spinning Nidec might be used.
Check the hub first, to get some idea what class
of fan is used.

For example, they have the option of using a 12V @ 1A
fan (12W), then reducing the voltage to it. Then,
when they turn it up to the full 12V, it draws the 1A
and provides a *lot* of airflow.

But for many power supplies, the fan speed is fixed and
there's no need for overrating and dynamic cooling settings
and "Hoover behavior". The most modern power supplies
are getting pretty efficient (as long as you draw
mostly from the 12V rail), and the fan can be pretty
wimpy in those.

Paul