Path: utzoo!attcan!uunet!umbc3!motteler
From: motteler@umbc3.UMBC.EDU (Howard E. Motteler)
Newsgroups: unix-pc.general
Subject: Re: fan mail
Summary: He's right
Keywords: cooling, fan, power supply.
Message-ID: <1891@umbc3.UMBC.EDU>
Date: 9 Apr 89 20:14:41 GMT
References: <157@bongo.UUCP> <1886@umbc3.UMBC.EDU> <161@bongo.UUCP>
Reply-To: motteler@umbc3.umbc.edu.UMBC.EDU (Howard E. Motteler)
Organization: University of Maryland, Baltimore County
Lines: 52

In article <161@bongo.UUCP> julian@bongo.UUCP (julian macassey) writes:
> [ regarding adding a second fan ]
>    This appears to be a good idea. One of the first things that occured to 
>me was to take the piece of foam rubber out of the fan slot on the left 
>hand side of the machine and slap in another fan. Obviously, two fans would 
>be twice as good. I mentioned this simple but brilliant mod to Gary Sanders 
>n8emr@gws and he said "No". Here was his story. The early systems were 
>shipped with two fans, but that caused air stagnation and hard disks were 
>overheating and failing all over the place. So there is a reason you only 
>get one fan, it is not because AT&T were too cheap to spring for a second 
>fan. So judging from that and what I have read in this group, the tip seems 
>to be: Go for a hefty AC fan and put up with the noise. 

This sounds like good advice, although I've been running for a year
and a half with a 2 fan 3b1 with the 80 meg mimiscribe, and no
problems.  But then I pulled the "electrostatic shield" off the hard
disk (along with the row of tin "fingers" in the back, and the monitor
"ground finger"--it's still grounded thru the cable shield), so air
can circulate around it a bit more freely.  Warning: doing that may
make the machine put out more RF noise, although mine shared a living
room with a color tv, fm "wireless headphone" and various radios, with
minimal effect.  A US robotics modem I had put out far more RF noise.

Actually, my motive was not so much cooling as (acoustic) noise: I'm
feeding a pair of DC fans at reduced voltage, which draw a bit more
air than a single DC fan, and only a little more current.  Because
each fan spins slower, the total noise is quite a bit less.  The
Miniscribe also had an annoying "ringing"--a resonance that I got rid
of this by gluing a couple of quarters to the top of the case.

A negative side effect of drawing more air thru the machine is that if
you leave the keyboard off the shelf, more air gets sucked in thru the
floppy drive, and it (or the whole machine, for that matter) can get
gummed up with dust fuzzies faster.

I did a number of experiments with different fan configurations,
letting the machine run for a couple of hours each time, and then
quickly popping it apart, to see if anything was getting too hot.  I
even tried switching the fans around to blow air INTO the machine, so
that I could filter air being sucked IN thru the fan grates.  (This
worked, but not all that well, and blew warm air on your fingers...
possibly a plus for typing, if your room gets a cold as you said :-)

Probably the most important "cooling hint" for ANY user: DON'T BLOCK
THE LITTLE GRILLE OVER THE POWER SUPPLY (below the monitor, on the
right hand side).  A sheet of paper laid here can get sucked down
aginst the grill, blocking a direct airflow to all those hot little
cooling fins on top of your power supply.

-- 
Howard E. Motteler       |  Dept. of Computer Science
motteler@umbc3.umbc.edu  |  UMBC, Catonsville, MD 21228