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From: kermode@shiva.trl.OZ.AU (Roger Kermode)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: The Fanning of the Amiga
Message-ID: <1991Jun12.062807.4584@trl.oz.au>
Date: 12 Jun 91 06:28:07 GMT
References: <3004@public.BTR.COM> <1339@cbmger.UUCP> <3025@public.BTR.COM>
Sender: news@trl.oz.au (USENET News System)
Organization: Telecom Research Labs, Melbourne, Australia
Lines: 58

thad@public.BTR.COM (Thaddeus P. Floryan) writes:

>As a for-instance, I can look at ANY one of my Amigas at home or at the office
>and clearly see where the air enters the systems due to:

>	dust buildup at the expansion port connector (A1000),
>	dust buildup around the external video/floppy connectors,
>	dust buildup around the joystick connectors, and
>	dust buildup in and around the floppy drive(s).

>The dust buildup around the floppy drive(s) is the worst ... what has happened
>to me many times is the optical sensor that detects the write-protect tab on a
>floppy gets obscured thus permitting the floppy to be (potentially) written-to
>(which is NOT nice in a virus-infested real-world).

>Though it's been nearly 30 years since I've taken any course in thermo-dynamics
>(and I've forgotten most of it/them :-), I'd like to cite one practical, real-
>world observation that anyone can verify:

>	a fan blowing ONTO a power supply will keep the supply cooler than
>	will a fan sucking air OVER a power supply.

>Since one of my companies used to make the power supplies for modem companies
>such as Ven-Tel, Racal-Vadic, and others (over 25,000 power supplies a month),
>I have a large notebook of measurements of various tests made using fans and
>YSI thermocouples regarding power supply heating, cooling, and related probs.

>If you want to perform a simple test for yourself, quickly go do some exercise
>and work up a sweat.  Then choose to cool off by either:

>	(a) standing in front of a fan blowing on you, or
>	(b) standing behind a fan sucking air around you.

>I'm sure you'll quickly agree that choice (a) cools you better!   :-)

I agree, but the power supply is not the one and only thing that has to
be cooled inside the amiga. In the A1000 the fan blows air out of the case,
air taken from the power supply which is in turn taken from the rest of the
A1000s inards. If this fan was blowing air in it would be blowing *heated*
air over the ICs, decreasing the effective rate of cooling.

Why not move the blow type fan so that it blows the air over the ICs and out
through the power supply? The answer to this was given in a previous post,
it's much easier to *control* the air flow inside the case using a suck type
fan which creates a marginal negative air pressure inside the case relative
to the air pressure outside the case. Air flow is then controled by the
aperture size of the vents in the comoputer case and the way obstacles are
arranged within the case. This method allows for much greater *control* of
the air flow over a *wider* area inside the case ensuring that *all*
components can be kept within their specified operating temperatures.

>Thad Floryan [ thad@btr.com (OR) {decwrl, mips, fernwood}!btr!thad ]


Roger Kermode, Telecom Research Laboratories | " I didn't do it,
ACSnet[AARN/Internet] r.kermode@trl.oz[.au]  |   they didn't see me do it,
Snail : PO Box 249 Clayton, Victoria, 3168,  |   they can't prove a thing!"
STANDARD DISCLAIMERS APPLY                   |    - Bartholomew J Simpson