Re: ATM DC cooling fans wiring question

["Alan Garcia" <ngarcia@columbus.rr.com>]

Why worry about slowing the fans down at all?  After lots of experimentation
and observation, I find it's best to blow as much air as possible on the
front and backside of the mirror during the entire observing session.
However, adequate vibration dampining is important and should be given due
consideration.

A. Garcia


----- Original Message -----
From: <Leftfieldstar@aol.com>
To: <mikell@optonline.net>
Cc: <atm@shore.net>
Sent: Thursday, December 13, 2001 1:36 PM
Subject: Re: ATM DC cooling fans wiring question


>
>  To all,
>
>  A few months back there was much discussion about controlling fan speed
and
> what circuits would work. I launched into a series of breadboarding
projects
> to get a sense of what circuits worked best with brushless DC motors.
>  The use of a MOSFET proved to be the simplest approach driven by a pulse
> width modulated circuit. The cookbook PWM circuits you will find thru
> websearches all switch at too slow of a rate to smoothly vary the power to
> the fan motor. However, if you raise the PWM rate to ~40 to 50 Khz
switching
> rate, you can easily vary the speed of the motor without any of the noise
> artifacts and stumbling encountered at the typically slower switching
rates
> that most of these circuits found in cookbooks use. The basic circuit also
> makes an ideal power controller for use as a heater for dew prevention on
> your diagonal.
>  Anybody wanting further assistance, contact me off list.
>
> It's a rainy day in Maine,
> Dominic DiLeo
>
>