"Trevor Wilson" wrote in message

"Arny Krueger" wrote in message
...
"WindsorFox[SS]" wrote in message
news:jW_Za.10115$qf.4685@lakeread06

Right, I wondered what a 12 Volt fan had to do with your
question, it's so cross posted now I thought I'd missed something
and was just replying to the 12V comments.

I plead guilty to bringing up 12 volt fans. I did so because 12 volt
fans are plentiful and readily adjustable. They can be adapted for
use where
the
original fan was 12 volt when DC power is readily available, such as
in a power amp.

I've experimented with fan speed controls on 120 VAC fans, and had
disappointing results. 120 VAC fans are based on synchronous motors
and IME
they get pretty ugly at low speeds if you turn their speed way down.

**Then you're not doing it right.

Letsee fan, resistor...

With simple series resistors and a
decent fan, speed reductions of at least 40% may be obtained very
easily, cheaply and reliably.

Just a second. Wasn't 60% reduction somehow inadequate when the fan in
question ran off of 12 volts?

With more sophisticated methods, an AC
fan may be controlled almost down to 0RPM.

I suspect the same can be said of 12 volt fans.

This cannot be achieved with DC fans.

Nor is there any need to do such a thing.

About 40% of max RPM is the best that can be attained.
Even within that range, 'cogging' is a real possibility. Ultimately,
lowering the speed of an AC fan will most likely provide worthwhile
noise reductions, whilst the cogging which occurs with DC fans, when
lowering their speeds, may create more problems than it solves.

There is no reason why a 12 volt fan would "cog" any more than a 60 Hz AC
fan. I've definately seen 60 Hz fans cog when trying to slow them down.
There's a tendency for AC fan motors to run synchronously.

I come back to the requirements of the original poster. He has already
stated that his preference is for extreme simplicity.

I have Phil Anderson's initial post here right here before me. I see no
requirement for extreme simplicity.

A series resistor on the original AC fan, is overwhelmingly the
appropriate
choice, for this guy.

In his inital post Phil said he tried that, and he had stalling problems.

That may not be the case for others.

What's simpler than an off-the-shelf fan speed regulator?