Chuck Kelsey wrote:
> Maybe I'm missing something here, but I've never subscribed to the theory of
> having fans run beyond PTT. What purpose does it serve? The transistors are
> generating heat only when they are "on." As soon as they are "off" they
> begin to cool down on their own. If the fans are doing their job, they are
> keeping temperatures to a prescribed level the entire duration of transmit.
> While running the fans beyond the end of transmit will cool the finals after
> the end of the QSO quicker than without, why should it matter?
>
> Chuck
> WB2EDV
>
Hello from Adam Kb2jpd
Fan timers are necessary whenever people are in close proximity to air
cooled electronic equipment. However, in the vein of Repeater-Builder,
most repeaters are installed in hostile installation environments
adjacent to other heat-producing electrical and electronic equipment.
Most of my installations have been in carbon coated elevator rooms with
temperature ranges from 80 degrees F to 130 degrees F. Fan timers
without temperature input sensors are not a real help here.
If you want to install an fan, it has a purpose, to move air. A lot of
times, it amazes me to see how much equipment is designed with no
temperature sensor to monitor and throttle the cooling system of these
repeater systems. It also amazes me that some fundamental equipment
necessary for repeater operation was not designed with physics of
thermodynamics in mind.
Last repeater I designed, I made sure a heat channel was in back , vents
to allow heated air to rise were in place , vents on the bottom for
whatever cool air entered, air filters on the bottom were installed. I
bought an repeater ampilifer and my partner installed it and it lasted
all of 24 hours. He took the puffin fan array I had in there blowing the
hot air up and away and was blasting it with downward hot air. Nice.
You can design one fan timer with two ro more inputs using transistor or
usual list of suspects like the 555.
73 Adam
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