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3.3.5 Cooling Fans
All adjustable frequency drives in this size range are equipped with cooling fans to provide airflow
along the heatsink. Units in NEMA 1 (IP21) and NEMA 12 (IP54) enclosures have a fan mounted
in the enclosure door to provide additional airflow to the unit. Chassis (IP00) enclosures have a
fan or fans mounted to the top of the unit for additional cooling. Some adjustable frequency drives
in this size range have a small 24 VDC fan mounted on the input plate. This fan is only mounted
on E-frame size units equipped with both an RFI filter and electrical fuses. The fan provides air
flow around the electrical fuses. The fan operates anytime the adjustable frequency drive is pow-
ered.
All fans are powered by AC line voltage which is stepped down by an autotransformer and regu-
lated to 200 or 230 VAC by circuitry provided on the power card. On/off and high/low speed control
of the fans is provided to reduce overall acoustical noise and extend the life of the fans.
Fans are activated by the following causes:
60% of nominal current exceeded
Specific heatsink temperature exceeded (power size dependent)
DC hold active
DC brake active
Pre-magnetization of the motor
Automatic motor adaptation in progress
Regardless of the heatsink temperature, the fans are started shortly after main input
power is applied to the adjustable frequency drive.
Once fans are started, they will run for a minimum of 10 minutes.
3.3.6 Fan Speed Control
The cooling fans are controlled with sensor feedback which regulates fan operation and speed
control as described below.
1.
IGBT thermal sensor measured temperature. The fan can be off, low speed, or high
speed based on this temperature.
IGBT Thermal Sensor
D Frame Units
E Frame Units
Fan Turn On Low Speed
113°F [45
°
C]
113°F [45
°
C]
Fan Low Speed to High Speed
122°F [50
°
C]
122°F [50
°
C]
Fan High Speed to Low Speed
104°F [40
°
C]
104°F [40
°
C]
Fan Turn Off from Low Speed
86°F [30
°
C]
86°F [30
°
C]
Table 3.1: IGBT Thermal Sensor
2.
Power card ambient temperature sensor measured temperature. The fan can be off or
high speed based on this temperature.
3 Internal Adjustable Frequency Drive Opera-
tion
High Power Service Manual for VLT
®
FC Series
Adjustable Frequency Drives
3-12
MG.90.L1.22 - VLT
®
is a registered Danfoss trademark
3
Summary of Contents for VLT HVAC FC 100
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