SmartFan
controllers function to proportionally control fan/blower
speed to maintain a nearly constant temperature. Under
difficult thermal conditions, fan speed is automatically
increased. Under more normal conditions, fan speed is
reduced to idle (about one-half speed), substantially
reducing acoustical noise.
Additional
information on operating principles, choosing Control
Temperature and cooling system noise control can be
found in the Technical
Data section.
Fan/Blower
Size
Size
the air mover for worst-case thermal conditions. Don’t
compromise available air flow. The controller will power
the air mover only as necessary to maintain the selected
Control Temperature. Consider allowing maximum flow
some-what greater than for a fixed speed design.
AC
or DC Power
Once the cooling power requirements are set, the choice
of AC or DC power is made. In HVAC applications and
in some electronic cooling applications at power levels
above 100 watts, AC power is usually preferred. At lower
power levels in electronic applications, DC power is
usually preferred because it is readily available, avoids
high voltage AC wiring and provides air flow that is
independent of power line voltage and frequency.
Any
quantity of air movers can be powered by a single
controller as long as the total power or current rating
of
the controller is not exceeded.
Configuration
and Operating Principle
The
Selection Guide
is an aid in selecting the most suitable controller.
DC controllers use either a switching or linear operating
principle. Switching offers the advantages, (at higher
power levels), of smaller size, lower cost, and high
power efficiency. Linear controllers are least expensive
at low power levels. Both switching and linear controllers
apply a smooth DC voltage to the air mover, permitting
a wide speed range with minimum acoustical and electrical
noise. AC controllers use a triac phase control principle
to vary the AC voltage applied to the fan.
Derating
Data
Maximum power and current for SmartFan controllers depends
on ambient air temperature and velocity. Data pages
give ratings at 55°C both in a low velocity air stream
(200 ft/min) and in still air. For controller operation
at air temperatures exceeding 55°C, use the derating
curves below.
Click
on image for larger version
Control
Temperature
Control Temperature is simply the temperature to be
held constant by the SmartFan controller. SmartFan’s
controlled sensitivity results in a sensor temperature
change of 3° to 4°C in the control region. This “slope”
partly compensates for the change in air-to-junction
temperature due to changing air velocity, resulting
in nearly constant junction temperature for typical
ICs. It also ensures control system stability.
Example
The
table below serves as a guide in selecting Control Temperature.
The shaded area represents typical applications. The
inlet air temperature below which fans idle (at about
half speed) is red. The inlet air temperature above
which fans run at full speed is black. Between these
temperatures the fan speed is controlled for a nearly
constant temperature at the sensor location.
A
system is designed such that with fans running at full
speed, the temperature rise from inlet to the sensor
location is 7°C. Choosing a 40°C Control Temperature
will result in fan idle speed for inlet air (room) temperatures
below 23°C. Fans will reach full speed at an inlet air
temperature of 33°C.
Lower/Upper
limits of Control Region for Inlet
Air Temperature
Click
here
Positioning
the Temperature Sensor
For
controllers requiring a temperature sensor, it is the
controller circuit and not the sensor that determines
Control Temperature. Air sensors are most commonly used;
however, surface sensors and immersion sensors are also
available.
Air
Sensors (P1,P4,P5,P6,P9,P10) SmartFan controls the temperature of air passing its sensor. This
temperature should relate to that of the air passing
over components and to the temperature of the components
themselves. For this to happen, the air must be in motion.
The sensor is usually placed in the exhaust air stream.
When choosing a location, consider that the effects
down stream from the sensor are outside the control
loop and cannot be sensed. Avoid placing the sensor
near a hot device as this could result in heating by
radiation. Open loop controllers (P suffix such as 018L135PA)
function by compensating for changes in inlet air temperature.
The sensor is therefore placed near the inlet. Fan speed
is proportional to room temperature in the range from
23° to 35°C. Fans idle below 23°C while above 35°C,
they run at full speed.
Surface
and Immersion Sensors (P3,P7,P8) These sensors are placed in direct contact with the surface or liquid
whose temperature is to be regulated. SmartFan then
controls fan speed to maintain near constant temperature.
Alarms
A
temperature alarm is included on many SmartFan speed
controllers. If the sensor temperature reaches 10°C
above Control Temperature the alarm is triggered. The
alarm is also triggered if fan power is lost.
Stand
alone alarms that sense temperature, fan speed or fan
current are also available. See design information on
alarms
Mounting
the Circuit Board
Circuit
boards are usually mounted using four snap-in plastic
spacers such as Richco CBS-4-19, or equivalent. Omni
SD should be mounted using metal spacers at hole locations
surrounded by conductive pads to minimize EMI. Hardware
packs, which include typical mounting and connecting
hardware, are available (see product pages). Note that
power ratings are greater when the circuit board is
mounted in an air stream (see product pages).
Vibration
Most fan noise is caused by the blades, with an additional
component due to motor vibration transmitted to the
mounting plate. At idle speed, depending on the design
of the mount, the motor component may become a significant
contributor. Should this situation be encountered, vibration
isolation may help. Rubber grommets or Wellnuts may
be used.
Testing
Tips
SmartFan must be tested in a complete cooling system
(except for open loop controllers with a P suffix in
their part number); that is, the sensor must be in the
controlled fan’s air stream. Using a heat gun or hair
dryer directly on the sensor forces its temperature
from below Control Temperature to above so quickly that
the fan may seem to “switch speed.” The hot air is not
being forced by the fan but by the hair dryer, and the
fan, therefore, cannot control it. To operate air movers
at full speed for test purposes, short-circuit the sensor
terminals. The sensor may be left connected or removed.
EXAMPLE
SmartFan®
vs. a Fixed Speed
Design
| Fixed
Speed Design A
cooling system is configured to use a fan rated
at 3000 RPM (full speed) to provide a flow of 200
CFM. Because the noise at 3000 RPM is excessive,
the fan is run at a reduced speed of 2200 RPM, where
noise is marginally acceptable. Air flow is less
than desired so that under worst-case conditions,
temperatures are excessive. The design is definitely
a compromise. |
SmartFan
Design The
same 3000 RPM, 200 CFM fan is used. A Control Temperature
of 40°C is chosen and the controller adjusts speed
automatically, depending on environmental conditions,
to hold exhaust air temperature at 40°C. Under typical
installation conditions of 23°C (73°F) at sea level,
the fan slows to 1500 RPM where its noise level
is 15 dB(A) lower than at 3000 RPM, and 8 dB(A)
lower than that of the fixed speed design. Increases
in thermal load due to higher room temperature,
greater system power, or factors such as higher
altitude or higher system flow resistance cause
the fan to increase speed to hold temperature at
40°C. Under worst-case conditions the fan reaches
3000 RPM where it provides nearly 40% more air flow
than the fixed speed design |
|
