On Tue, 12 Aug 2003 18:53:57 GMT, "Trevor Wilson"
wrote:


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

Further proof that little knowledge is worse than no
knowledge at all. He was taking about SYNCHRONOUS MOTORS.
Putting resistors in series with a synchronous motor is
folly.



With more sophisticated methods, an AC fan may be controlled
almost down to 0RPM. This cannot be achieved with DC fans. 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.

I come back to the requirements of the original poster. He has already
stated that his preference is for extreme simplicity. A series resistor on
the original AC fan, is overwhelmingly the appropriate choice, for this guy.
That may not be the case for others.