| | | Author | Message | | | eric | | Posted: Sun Sep 10, 2006 9:33 am Post subject: Slowed-down fan | | | | Site Admin Joined: 01 Jan 1970 Posts: 311 | K.S.M. Walraven
If, like many other people, you
have ever been annoyed by the
noise of, say, the extractor fan in
your bathroom, here’s a tip that
may quieten things down a bit.
The fans in bathrooms and
cooker hoods are normally
small ones that rotate at high
speed (but note that many
cooker hoods have a speed control).
The idea is to displace many cubic feet of air at little cost.
Fortunately, the speed of these fans can be lowered fairly simply
by placing a resistor in series with the motor. The impedance,
Z, of the fan is calculated from
Z=U2/P,
where P is the rating of the fan, and U is the working voltage, normally
the mains voltage. If, for instance, the rating of the fan is
33W, and the mains voltage is 230 V, its impedance is 1600 Ω, give
or take an ohm.
The series resistor should have a value of about 1/3 of this
value, that is, 47
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