"Ron" wrote in message
...

I wish I'd known how difficult controlling a 12VDC fan was;
I wouldn't have done it. I have two fans, fed by a self
designed and built controller. An IC sensor (output volatge
linearly related to temperature) feeds a servo circuit
(separate one for each fan) that keeps it running at the
lowest speed that will produce 50 degrees C at the power
amplifier heat sinks (I have two Aragon Pwier amps, 2 and 3
channels respectively, that sit in an enclosed cabinet).
Cogging is prevented by starting each fan only when its
drive voltage is greater then 6V. The circuit is simp.icity
itself, (3 ICs).

This have been working reliably for a few years now and
shows no signs of difficulty. The amps never overheated. The
fans are standard 12VDC fans, chosen for lowest noise. They
don't know how difficult what they are doing is, either.

**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.


--
Trevor Wilson
www.rageaudio.com.au