"Arny Krueger" wrote in message
...
"Trevor Wilson" wrote in message


**No, difficult as in reducing the speed to a reasonably low level
(say: 10% of max RPM).

Straw man argument. Knocking fan speed down to 40% of rating makes a very
dramatic change in noise and air flow.

**Not if cogging occurs. A real possibility with DC fans.


If a really weak 120 mm fan is required, a couple of days ago I
recommended
fabricating a baffle plate (15 minutes) and using a smaller fan. If a
wider
range of air flows is required, using a switched array of fans would be a
solution.

**Points:

* Fabrication times of 15 mins, assumes the OP ahs the appropriate
facilities.
* It would take far longer than 15 mins to remove the original fan from the
Ampzilla.
* It would take considerably less time to choose an appropriately sized
resistor, for the existing fan.


And further, the original poster expressed
some trepidation about placing a series resistor in circuit with a
110VAC fan.

IME, a basically ugly process that works even worse with 120 volt fans
than
changing the speed of 12v DC fans. Series resistors have been largely
superceded by variable regulators (often PWM in the case of motherboard
fan
regulators) in 12 volt fan applications because of the problems with
stalling.

**I'm sure they're very effective on mother boards. They may not be
appropriate for the OP, given his preference for a simple solution.


A regulator is a fair bit more complex than that.

Except that I provided a reference to an off-the-shelf pre-packaged
regulator unit.

**Which is still far more complex to implement than a series resistor.


The statement that 12 volt fans are difficult to control is truly the
voice
of inexperience. The claim that modern DC fans incorporate their own AC
power supplies is true as far as it goes, but it's not a fixed AC
frequency.

**It may not be. They're still not as controllable as a fan whose motor is
directly accessible. And for the record: I have quite a bit of experience in
controlling all sorts of fans, including DC motor ones.


--
Trevor Wilson
www.rageaudio.com.au