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Unidrive User Guide
25
Issue Number: 9 www.controltechniques.com
Example
To calculate the size of an enclosure for the following:
•
Two UNI1405 models
•
Each drive to operate at 4.5kHz PWM switching frequency
•
RFI filter for each drive
•
Braking resistors are to be mounted outside the enclosure
•
Maximum ambient temperature inside the enclosure: 40
°
C
•
Maximum ambient temperature outside the enclosure: 30
°
C
Dissipation of each drive: 190W
Dissipation of each RFI filter: 7.7W (max)
Total dissipation: 2 x (190 + 7.7)
=
395.4W
The enclosure is to be made from painted 2mm (0.079 in) sheet steel
having a heat transmission coefficient of 5.5W/m
2
/
o
C. Only the top, front,
and two sides of the enclosure are to be free to dissipate heat.
Figure 3-15 Enclosure having front, sides and top panels free to
dissipate heat
Insert the following values:
T
int
40
°
C
T
ext
30
°
C
k
5.5
P
395.4W
The minimum required heat conducting area is then:
=7.2m
2
(78ft
2
)
(1m = 3.3 ft)
Estimate two of the enclosure dimensions - the height (H) and depth (D),
for instance. Calculate the width (W) from:
Inserting
H
= 2m and
D
= 0.6m, obtain the minimum width:
= 1.8m (6ft)
If the enclosure is too large for the space available, it can be made
smaller only by attending to one or all of the following:
•
Using a lower PWM switching frequency to reduce the dissipation in
the drives
•
Reducing the ambient temperature outside the enclosure, and/or
applying forced-air cooling to the outside of the enclosure
•
Reducing the number of drives in the enclosure
•
Removing other heat-generating equipment
Calculating the air-flow in a ventilated enclosure
The dimensions of the enclosure are required only for accommodating
the equipment. The equipment is cooled by the forced air flow.
Calculate the minimum required volume of ventilating air from:
Where:
V
Air-flow in m
3
per hour
T
ext
Maximum expected ambient temperature in
o
C
outside
the
enclosure
T
int
Maximum permissible ambient temperature in
o
C
inside
the
enclosure
P
Power in Watts dissipated by
all
heat sources in the
enclosure
k
Ratio of
Where:
P
0
is the air pressure at sea level
P
I
is the air pressure at the installation
Typically use a factor of 1.2 to 1.3, to allow also for pressure-drops in
dirty air-filters.
Example
To calculate the size of an enclosure for the following:
•
Three UNI3401 models
•
Each drive to operate at 6kHz PWM switching frequency
•
RFI filter for each drive
•
Braking resistors are to be mounted outside the enclosure
•
Maximum ambient temperature inside the enclosure: 40
o
C
•
Maximum ambient temperature outside the enclosure: 30
o
C
Dissipation of each drive: 670W
Dissipation of each RFI filter: 12.8W (max)
Total dissipation: 3 x (670
+
60) = 2048.4W
Insert the following values:
T
int
40
°
C
T
ext
30
°
C
k
1.3
P
2048.4W
Then:
= 799m
3
/ hr (471ft
3
/ min)
(1m
3
/ hr = 0.59ft
3
/min)
W
H
D
A
e
395.4
5.5 40 30
–
(
)
---------------------------------
=
W
A
e
2HD
–
H D
+
--------------------------
=
W
7.2
2 2
×
0.6
×
(
)
–
2 0.6
+
----------------------------------------------
=
V
3kP
T
int
T
ext
–
---------------------------
=
P
o
P
l
-------
V
3 1.3
×
2048.4
×
40 30
–
------------------------------------------
=
Summary of Contents for Unidrive 1 Series
Page 208: ......
