Basic electrical methods for stealth fan oporation
Fan Speed Control 101
I. Know your fan In
order to control fan speed, you have to know what type of motor your
fan uses. Motors can be divided into two categories based on power
source AC, and DC. AC fans are those you plug directly into a wall
receptacle (Vortex, Dayton, Can-Fans), for more information about AC
motors go to numeral II. DC motors are generally found in small fans
like computer fans and rely on a DC power source like a rectifier (wall
wart) or battery. For more information about DC fans, see numeral V.
AC fan:
DC fan:
II. Know More About Your Fan AC fans use many types of motors but three types are important to us cabinet-bedroom size growers, shaded pole induction motors, permanent-split capacitor (PSC) motors, and AC-DC Universal motors (Brushed Motors).
For a list of motor type based on manufacturers, see numeral III.
Shaded pole induction motors are simple single phase motors known for
low starting torque and long duty cycles. PSC motors are also single
phase motors but unlike shaded pole motors, PSC motors use a capacitor
to help them start. AC-DC Universal motors are general purpose motors
found in many household appliances like power drills and vacuum
cleaners; their short service life makes them an unattractive option
for fans. There are other types of AC motor that have been used for
ventilation purposes, but aside from shaded pole, PSC, brushed motors,
and three phase motors (which are beyond the scope of this course), ac
motors are unable to be speed controlled without serious modification
and/or risk. There are primarily two ways to control the speed of
these motors, voltage control and frequency control; see numeral IV for
more information.
III. Fan Manufacturer List This
information is relevant as of march 2009 but always be sure to double
check by contacting your retailer or fan manufacturer! Using the wrong
type of control with your equipment puts the fan and your controller at
risk. This section is always in need of additions and corrections so if
you have anything to add, post it or send me a P.M. and I'll be sure to
include it.
Permanent-Split Capacitor -Dayton squirrel cage blowers (Generally PSC motors, but they also make a shaded pole version) -S&P Mix-Vent TD line -Grainger squirrel cage fans
Shaded Pole Motor -Vortex -Can-Fan -Valueline -Elicent -Active Air
IV. AC Speed Control Methods
Voltage -Rheostat (Old dimmer switches): Poor choice, excess power converted to heat.
-Triac (New dimmer switches): Poor choice, inherent problems with triac controls risk fan lifespan.
-Triac
w/ Snubber circuit (Fan speed controllers, Solid state controllers):
Good choice, snubber circuit removes most of the risk to the fan. Still
not the best because it can cause some motors to hum.
-Capacitance
level control (No hum fan speed controllers, 3 speed controllers): Good
choice, only limited by the discrete speed choices, no infinite control.
-Variable
autotransformer (Variac): Better choice, continuous sine wave of a
lower voltage (unlike a triac which chops up the sine wave to acheive a
decreased voltage) allows fan operation with no hum.
Frequency -Varable
Frequency Drives (VFD, AFD): Best choice, complex circuitry senses
changes in the motor allowing it to vary frequency of the AC source as
well as the voltage which maintains a constant torque, unlike voltage
regulation.
V. DC Speed Control Methods DC
speed control is much simpler than AC speed control. In order to lower
the speed of a DC motor we must lower the voltage, this is accomplished
in various ways. Linear voltage regulation relies on resistors, and
diodes to remove the excess voltage as heat. Pulse Width Modulation
sends bursts of energy to the fan and the averaging effect results in a
lower net voltage and reduced energy use.
