On Tue, 22 Jul 2008 12:18:56 -0400, Meat Plow
put finger to keyboard and composed:

On Tue, 22 Jul 2008 16:18:49 +1000, Franc Zabkar wrote:

On Mon, 21 Jul 2008 17:58:34 -0400, Meat Plow put
finger to keyboard and composed:

On Tue, 22 Jul 2008 07:19:40 +1000, Franc Zabkar wrote:

On Mon, 21 Jul 2008 12:54:35 -0700, "David Farber"
put finger to keyboard and composed:

Just to clarify a few things, the 6.3k reading was taken in circuit and
it is not mounted on a heat sink. For test purposes, I installed the
fan with the component in question bypassed. It seemed to operate at
too high a speed and it was almost as loud as a gas powered leaf
blower. So I shut it down and will wait for the new fan to proceed.

If it is a thermistor, then there must be two connections to the red
wire, one for the thermistor and another for the fan motor and the
electronics. I presume the white (?) wire is the RPM output.

But if it is a thermistor, or a thermal fuse, then how does it sense
the temperature if there is no airflow? Or does the fan always turn at
some minimum speed, regardless of temperature?


Fan speed would be controlled by the mainboard via CPU core temp. Most
fans on newer mainboards run full speed when the PC is first switched on.
Some wait a few seconds and then throttle the fan speed back to 1850 RPM.
Some are much quicker to throttle. This is the behavior on my MSI AMD
Athlon X64 and Intel 865 P4 mainboards.

IMHO, the only proper way to control fan speed is by using a 4-wire fan,
ie one where the voltage supply to the fan's motor and electronics is
constant and the speed is varied by means of a PWM input signal. Trying to
control a 3-wire fan by chopping its supply would result in the RPM output
signal being chopped as well. It may also cause the fan's electronic
commutation to misbehave, or make strange noises. Smoothing the output
voltage with an inductor and capacitor may improve the performance, but
it's still not ideal.

A fan that is internally temperature controlled would behave
unpredictably. For one thing, reducing the voltage to the potential
divider that contains the thermistor would result in incorrect temperature
feedback. Here is an example where reducing the voltage to such a fan
actually *increases* its speed:

Well complain to Dell, Intel, MSI, ASUS etc.. I'm just making an
observation.

There is nothing to complain about if the speed control is done
properly. When it's done incorrectly, however, this is what you get:

What is the influence of PWM on fans' reported RPMs?
http://www.almico.com/sfarticle.php?id=1

SpeedFan's author is talking about a 3-wire fan which is what the OP
has.

I think you'll find that Intel is now specifying 4-wire fans for those
cases where speed control is external to the fan, and 3-wire fans when
internal temperature sensing is used. It's possible that your fans are
one of the above types.

- Franc Zabkar
--
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