Unidrive M / HS Frame 7 to 10 Power Installation Guide 35
Safety information Product information
Mechanical installation
Electrical installation Technical data UL listing information
3.5.3 Enclosure sizing
1. Add the dissipation figures from section 5.1.3 Power dissipation on page 98 for each drive that is
to be installed in the enclosure.
2. If an external EMC filter is to be used with each drive, add the dissipation figures from section
3.9.2 EMC filter ratings on page 44 for each external EMC filter that is to be installed in the
enclosure.
3. If the braking resistor is to be mounted inside the enclosure, add the average power figures from
for each braking resistor that is to be installed in the enclosure.
4. Calculate the total heat dissipation (in Watts) of any other equipment to be installed in the
enclosure.
5. Add the heat dissipation figures obtained above. This gives a figure in Watts for the total heat that
will be dissipated inside the enclosure.
Calculating the size of a sealed enclosure
The enclosure transfers internally generated heat into the surrounding air by natural convection (or
external forced air flow); the greater the surface area of the enclosure walls, the better is the
dissipation capability. Only the surfaces of the enclosure that are unobstructed (not in contact with a
wall or floor) can dissipate heat.
Calculate the minimum required unobstructed surface area A
e
for the enclosure from:
Where:
A
e
Unobstructed surface area in m
2
(1 m
2
= 10.9 ft
2
)
T
ext
Maximum expected temperature in
o
C outside the enclosure
T
int
Maximum permissible temperature in
o
C inside the enclosure
P Power in Watts dissipated by all heat sources in the enclosure
k Heat transmission coefficient of the enclosure material in W/m
2
/
o
C
Example
To calculate the size of an enclosure for the following:
• Two drives operating at the Normal Duty rating
• External EMC 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
For example, if the power dissipation from each drive is 187 W and the power dissipation from each
external EMC filter is 9.2 W.
Total dissipation: 2 x (187 + 9.2) =392.4 W
Power dissipation for the drives and the external EMC filters can be obtained from
Chapter 5 Technical data on page 92.
The enclosure is to be made from painted 2 mm (0.079 in) sheet steel having a heat
transmission coefficient of 5.5 W/m
2
/
o
C. Only the top, front, and two sides of the
enclosure are free to dissipate heat.
The value of 5.5 W/m
2
/ºC can generally be used with a sheet steel enclosure (exact
values can be obtained by the supplier of the material). If in any doubt, allow for a greater
margin in the temperature rise.
A
e
P
kT
int
T
ext
–
-----------------------------------
=
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