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From: wtm@neoucom.UUCP (Bill Mayhew)
Newsgroups: comp.sys.att,unix-pc.general
Subject: Re: Fan Recommendation
Summary: Fan on the left side is not a good idea
Message-ID: <1611@neoucom.UUCP>
Date: 2 May 89 15:17:27 GMT
References: <1567@jhunix.HCF.JHU.EDU> <485@limbic.UUCP> <664@devildog.UUCP>
Organization: Northeastern Ohio Universities College of Medicine
Lines: 32


The fan on the left side (the side where the floppy disk is)
doesn't seem like all that swift of an idea.  If anything, it
assists in sucking dust in through the floppy dirve slot.  If the
fan on the right poops out, the power supply is probably going to
get too hot anyway, as the left fan isn't going to pull a whole lot
of air from the right rear of the machine; it'll favor the floppy
slot.

Threre is thermal protection on the power supply in *my* 3b1, but I
suppose that isn't the case for all machines.  Now, mind you,
repeated short on/off cycles, isn't going to do a whole lot of good
for the integrity of the file system as the power supply repeatedly
cools and heats.  It could also be that the thermal protection
doesn't invoke soon enough to prevent deformation of the case due
to the heat build-up.

I've thought about either using a thermistor probe or an air flow
switch and an external controller to cut power when things get out
of hand.  A termistor would be fairly simple to implent.  The
termistor could be placed in series with a latch-up relay that
would prevent power cycling.  It might be possible to select a
thermistor and relay that wouldn't need any transistors, etc to
drive the relay.  If I get anywhere with the project, I'll post the
results.  I don't think there is enough of a static pressure drop
in the Unix PC case to make using an *inexpensive* commercially
available pressure sensor practical; one might be able to use a
vane air flow switch mounted outside the case with the fan blowing
on it.

Bill
wtm@impulse.UUCP