Variable-speed Unix PC fan

[Donald Lashomb]

In article <1990Jun25.205650.7200 at craycos.com> jrbd at 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