[Collins] Boat Anchor Fans

[Garey Barrell]

Air flowing through a piece of equipment carries dust particles with
it.  These particles tend to stick to things, either through oils,
dirt or electrostatic attraction.  Anything that increases the
_amount_  of air flowing through the device, increases the amount of
dust  _available_  to stick to things!   Aside from an electrostatic
filter cleaning all air admitted to the cabinet, the only choice is to
periodically open up the cabinet brush the accumulated dust loose and
suck it up with a vacuum.

The brand of fan, or the voltage it runs on, have nothing to do with
the amount of dust deposited; only the volume of air that is moved.
As Ray says, if you suck air out, then other air is going to flow in
behind it.  More air out, more air in to replace it!

With equipment that is designed for convection cooling, (MOST of our
gear,) the most efficient way to reduce the internal operating
temperature of the ENTIRE piece of equipment is to "encourage" this
convection.  This typically consists of a small fan on TOP of the
unit, EXHAUSTING the hot air within the cabinet UP and AWAY from the
unit.  Obviously, if the equipment is sitting under a shelf (usually
supporting still more equipment!) then the next best scenario is a fan
attached to the back of the cabinet blowing the hot air out that way.
We are not looking for "forced air cooling", but merely to get the
warm air out of and away from the cabinet.

Air cooling is a SYSTEM.  Consideration is given in the design process
to get heated air out of the cabinet in some specific way.  Any add-on
that does anything other than "encourage" the designed cooling system
is operating at reduced efficiency.  A fan isn't necessarily "more
efficient blowing than sucking."  The only thing that affects the
amount of air moved by a given fan is "back pressure", or resistance
to airflow.   Again, any air that is "blown" out the front has to be
"sucked" in the back.  Pesky physics rules.

One last example and I'll shut up.   (If anyone has actually read this
far.....)    The Drake TR-7 has a "cooling system" for the final
amplifier.  The SYSTEM was designed for the fan to "suck" air out the
back, and that is what Drake recommends.  Some after market "experts"
insist that the fan must be reversed to blow in because everyone
knows.......   Not true.  The final is way overspec'd, so it will work
either way, but actual measurement of the heatsink temperature shows
that it runs cooler with the fan blowing "OUT" the back.

73, Garey - K4OAH
Atlanta

----- Original Message -----
From: "Ray V." <w2ec@attglobal.net>

> Dave,
>
> Are you saying this "Boatanchor Cooler" fan system creates a total
> vacuum inside the Collins gear? I would think that if the fan is an
> exhaust system, removing air from the Collins gear, then external
air
> would have to re-enter the Collins gear to replace what is removed.
I
> would think that, unless the COllins gear is fully enclosed within a
> filtering system, then whatever air re-enters could bring with it
the
> dust, etc. How does the "Boatanchor Cooling" system filter the
incoming
> air to replace the exhausted air?
>
> I use the exhaust method as well, a simple $3.00 115vac muffin fan
> sitting on top of my KWM-2 and KWM-2A over the HV section drawing
air up
> and out, with little rubber bumper feet for protection of the case
> surface. This keeps the rig totally cool but of course I do keep an
eye
> on the insides for dust buildup etc.
>
> 73, Ray  W2EC
>
> David Knepper wrote:
>
> > The fans that are part of the "Boatanchor Cooler" system are
exhaust fans
> > that take warm air from inside the Collins and exhaust it outside
the unit.
> > No dirt, etc. can get inside the Collins as a result of the fan.
> >
> > Jose, you need to turn your fan around!
> >
> > David Knepper - W3ST