On Tue, 12 Aug 2003 12:38:40 +0100, Lived EHT
wrote:

On Mon, 11 Aug 2003 21:00:40 GMT, "Trevor Wilson"
wrote:

**You still can't lower the speed much below 40% of maximum PRM. That ain't
speed control. A resistor in series with an AC fan is just as precise.

Or he could use a simple PWM circuit to control the speed of the fan.
That should get it down as slow as he wants and would give the most
consistent results.

Wow... I am all aghast. Someone that actually knows how to
control a fan... My hat off to you, sir...

Actually, you can't go 'as low as you want', but 10% - 15%
is a piece of cake. Below that, the efficiency of the blades
is down to zilch.

I think a series resistor would yield variable
results, especially for low RPMs.

In addition, it will consume power and *add* to the heat.

-- Ron


OTOH, he could bypass the resistor
with a large capacitor to give full voltage for a brief moment when
the fan is turned on, hopefully avoiding a turn-on stall. Or maybe
make a variable voltage regulator that applies full voltage at turn-on
and then relaxes to the required minimum voltage over a period of a
second or two.