John Dunkley said:
I would be grateful for some advice on what is the most efficient way to
speed control an exhaust fan?
Not knowing much about motors, it is a 240 volt unit 0.45 amps.
**Assuming the motor is a synchronous type, your chances are limited. PA's
idea of a VariacT is ideal, but expensive and bulky. I know people who have
put a lamp in parallel with the motor and used a standard light dimmer. I
can't guarantee the results, but it should work. Another good way is to
place the motor in series with a bridge rectifier (and the mains supply).
Across the DC connections of the bridge, connect a MOSFET (suitable rated
and heat sinked, of course) and vary the Gate Volts to get speed control
that way. The advantage is the motor can be varied over a very wide range.