Why not just run 'em 24/7? I use DC fans exclusively and have run them
constantly for a quarter century. It gets cooled properly even when on
battery backup! Why bother turning them on or off?
----- Original Message -----
From: <[EMAIL PROTECTED]>
To: <Repeater-Builder@yahoogroups.com>
Sent: Tuesday, April 06, 2004 2:49 PM
Subject: RE: [Repeater-Builder] Thermostaticaly controlled fan cctt please ?
> I went this road a few years ago using the small button thermal switches
> (Switch Craft - etc.) that are available in a variety of on-off
temperatures
> settings, but it didn't prove overly successful. The small thermal
switches
> have to be heat sinked to the PA, so you have to route AC for the fan up
to
> some location on the PA heat sink, this is messy, not easy to implement,
and
> requires extra AC (hum) wiring running around the station. The switches
> don't have an impressive life cycle and many started going intermittent
and
> erratic in a year or so.
> The new approach I implemented is to use a solid state relay, they require
> nothing more than a logic level to drive them, which is easy to find about
> anywhere in the station or controller (most controllers have logic outputs
> that can be controlled by writing a simple macro command controlled by the
> PTT command). This isn't temp controlled, its time controlled, so fan
comes
> on with PTT command from the controller, fan continues to run for 4
minutes
> after PTT drops. ( I use this control scheme for PA and general cabinet
fan
> cooling operations on all my repeaters using SCOM 7K controllers)
> This has proven much more reliable over time than temp. control and you
will
> likely find the fans can do many more on-off cycles during their usable
life
> than the thermal switches. Solid state relays last a lifetime and cost
less
> than the thermal snap disc switches in many cases. The fan starts PA
> cooling process w/o waiting for PA to heat up before cooling can start and
> then try and play catch up; a 3 to 4 minute post PTT run time on the fan
is
> plenty of time to allow for more than sufficient cool down of any residual
> heat; this is where a thermal control switch can often cycle on-off
several
> times depending on the proximity of the thermal switch-fan-main heat
> sources, and size/density of the heat sink.
> The power consumption of a good muffin fan is about 4 to 8 watts, so even
if
> you have more run time using the timer approach it isn't going to amount
to
> 20 cents of electricity a month and you end up with something from my
> experience which has proven much more reliable in the long run. A side
> benefit to having the fan come on with PTT other than PA cooling is it
> supplies immediate air movement inside the cabinet for some cooling to the
> power supply, circulators, etc.
> So hope this is some help or insight for your application - Good Luck
>
> Rob K7EI
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