Path: utzoo!attcan!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!wuarchive!emory!att!att!fang!alfred!tous!tarpit!bilver!bill
From: bill@bilver.uucp (Bill Vermillion)
Newsgroups: comp.sys.misc
Subject: Re: fan question
Message-ID: <1990Dec17.015530.17483@bilver.uucp>
Date: 17 Dec 90 01:55:30 GMT
References: <9012130133.AA24147@polar.bowdoin.edu> <6606@suned1.Nswses.Navy.MIL>
Distribution: na
Organization: W. J. Vermillion - Winter Park, FL
Lines: 45

In article <6606@suned1.Nswses.Navy.MIL> zaft@nswses.navy.mil (Gordon C Zaft) writes:
>In article <9012130133.AA24147@polar.bowdoin.edu> poulin@POLAR.BOWDOIN.EDU (Jeff Poulin) writes:
>>Here's a dumb little question that I'm not sure of the answer.  Which
>>direction should the fan be blowing: into the power supply or out of it?
>>My computer came configured with the fan blowing in (presumably to keep
>>the stuff in the power supply cool), but I noticed the cards become quite
>>warm and one of the hard drives starts sounding like a car going 40mph in
>>first gear if I leave the computer on for more than 12 hours.  Otherwise
>
>	Fans on power supplies should never blow into the cabinet, always
>OUT.  The idea is to draw cool air into the cabinet, across the cards,
>through the power supply and out.

Just because IBM screwed up the original design there is no reason the
world has to follow.  Fans should always blow IN to a system.  And ideally
they should have a replaceable filter.

You have to design the cabinet properly, and your high draw chips should be
the near the exit - take a good look at an S-100 box that is properly
designed.

The problem with blowing out is that the air comes in at ALL entrances to
the system.  Venturi effects create higher velocities nearer smaller
openings and you such dirt into such thinks as chip sockets, and worst of
all THROUGH floppy drives.  That's a killer. 

Of the compatibles/clones Tandy had one run of their 3000 series that had a
a power supply enclosed in a wide slot cage.  The cooling fan drew in at
the front of the machine through a washable filter.  The air then came
directly across the memory chips, and out through the power supply.
They dropped that later - but it was one of the good things they did.
You will see this approach in many of the newer '486 boxes - and I saw one
that did the above, but used a dual stage fan depending on internal
temperatures.

Designers are finally starting to design things, not just copy a poorly
designed piece of equipment.


Pressurizing any component is the only real way to prevent hot spots, along
with proper layout.

-- 
Bill Vermillion - UUCP: uunet!tarpit!bilver!bill
                      : bill@bilver.UUCP