Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!n8emr!uncle!donlash
From: donlash@uncle.uucp (Donald Lashomb)
Newsgroups: comp.sys.att
Subject: Re: Variable-speed Unix PC fan
Message-ID: <1990Jun27.192139.28190@uncle.uucp>
Date: 27 Jun 90 19:21:39 GMT
References: <1990Jun25.205650.7200@craycos.com>
Reply-To: donlash@uncle.UUCP (Donald Lashomb)
Distribution: na
Organization: U.N.C.L.E.
Lines: 20

In article <1990Jun25.205650.7200@craycos.com> jrbd@craycos.com (James Davies) writes:
>I have a Unix PC (2 MB, 40 MB disk) which I bought new in
[...]
>noticed that occasionally the cooling fan sounds like it is
>slowing down or speeding up - i.e. as if it has two speeds, and
[...]
>problem) is that the fan is adapting to cooling requirements -
>when the system starts getting hot, the fan speeds up, and
>then slows down again when things have cooled off sufficiently.
>Does anyone out there know if this is the case?  Or do I have a
[...]


Yup, that's what's happenning, James.  The fan is powered directly off of
the power supply in the Unix-PC.  The (12v) feed for the fan on the power
supply has a "thermostat" in it.  When things get hot, it gives the fan
the full 12v.  During cooler times less voltage (6-7v ???) is given to the
fan.

-Don