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Re: hot PCF


I think I referred to "radial fans" in my prior note.  I meant "axial"
fans or more precisely, "tube-axial".  Radials fans would move a lot of
air but would probably be too noisy and expensive.

There are many factors that can be varied when making fans:  The key
features are air flow, noise level, required supply voltage, wattage,
and sleeve or roller bearing.  Most sellers of fans don't know or
reveal any of these factors.  Some do reveal one or two.  If you can
find a model you like you can look up the manufacturer and sometimes
get the specs.  I look for the biggest fan I can fit to my application,
then look for the highest airflow (if cooling is the number one
priority) or highest ratio of CFM to dbs (if noise level is an equally
high priority).  

www.mouser.com sells Augusta brand axial cooling fans and lists all the
relevant specs for each fan.  Prices range from around $8 or $9  for
some 3" fans to over $20 for 4 1/2" AC fans.  Check the "catalogue
page" to see the specs (  http://www.mouser.com/catalog/cat_607/422.pdf

The specs for airflow, if you can find them for the fans you're looking
at, are almost always the flow rated for totally unimpeded flow.  In
any practical application, you will probably get about half that

Most electronic supply houses will sell at least one or two models of
3" and/or 4" fans.  If a fan is DC powered, be sure to find out if it
comes with a transformer or if that's a separate purchase.

I have heard good things about the IceCap fan -- it has a thermostat to
trim the speed at lower temps and comes with a transformer included in
the price.

It will probably be hard to fit a useful fan on the end of stock hood. 
These hoods are made for housing much lower wattage bulbs.  They did
not leave room for a fan in their design.  The vents are placed to
provide some convection cooling for the ballast(s) but not the filament
ends of bulbs, which are what need it most with PCs and other high
output flourescents.  If you turn the hood facing bulb up towards the
ceiling, the bulb will run much cooler -- but this is generally not
regarded as a practical solution ;-)  But seriously, even if you fit a
fan on the end, it will be a small diameter and much of its airflow
will be probably be blocked by structures inside the hood (but within
limits small is better than none).  If the hood extends beyond the bulb
several inches, you can try mounting the fan on top of the hood at one
end, forcing air down and into the hood, with the exhaust opening at
the opposite end.  This will force two 90 degree turns for the air, one
flowing in and one at exit, and that will reduce the airflow compared
to the mounting on end arrangement, but it's another way to go.  In
fact, if you're thinking about mounting a fan on top of the hood, then
you might consider something like a Pabst flatpak fan (
http://www.ebm.com/series.asp?SeriesID=RG125AC  ) or other centrifugal
type fan.

BTW, the socket end of a PC bulb is the hottest end.  Just slowly wave
your hand an inch or two away along the length of the bulb -- very
different temp at the socket from the rest of the bulb!

For very little money, and a little construction skill, you can put
together a hood that fits your fan rather than trying to find a fan to
fit your hood.  I think AH Supply still has free enclosure plans for
its customers.

I would recommend at least about 3" fan for a 55 watt bulb, and at
least a 4.69" (4.5", 4.72") diameter fan for a 96 watt bulb.  But a lot
depends on having open airflow on the exhaust side of the fan, and an
exhaust opening on the hood that is at least as large in area as the
opening on the fan itself, preferably larger.  Given these things, I'd
suggest a fan with a rated airflow of about 40 to 50 cubic feet per
minute (CFM).

Also, you can try putting a large room fan, the kind that's anywhere
from 8" or more in diameter and comes on a floor stand, in your tank
room pointed at the tank, main the lights.  This can help in some
circumstances -- not cure, but help.  But any airflow should be
noticeably better than none -- even this just helps move hotter room
air out of the room.

Most of the electricity that goes into a light producing setup is
converted to heat, the trick is to move the heat away from the tank
before it hits the water.  If you think PCs are hot at about 35%
efficiency, just imagine if you had to light a planted tank with
incandescents, which are about 6-8% efficient.  Yes those round light
bulbs are actually very efficient small heaters, nearly all of the
energy going in comes out directly as heat.

Look on the bright side (no pun intended): Summer is almost over, and
ambient temps will soon decline so you have all winter to finish
whatever change you are going to make. :-)

Good luck,
Scott H.

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