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M’Ax Installation Guide
13
Issue Number: 6
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Crossing angle
When power and
signal cables
cross, the
crossing angle
must be 90°.
2.25
Enclosure calculations for heat
removal
Decide whether the enclosure is to be sealed or ventilated, as follows:
Sealed enclosure
A sealed enclosure can give a high ingress-protection rating, but with
reduced heat removal capabilities. If possible, locate heat-generating
equipment (other than braking resistors) in the lower part of the
enclosure to encourage internal convection. If necessary, a taller
enclosure, and/or air-circulation fans inside the enclosure, can be used.
For calculating the minimum size of sealed enclosure that will
adequately cool the drive (and other drives), see Enclosure calculations
later in this chapter.
Ventilated enclosure
If a high ingress-protection rating is not required, a ventilated enclosure
can be used with a fan to supply forced air cooling; this can give a lower
ambient temperature than a sealed enclosure. For calculating the
minimum required volume of cooling air, see Calculating the air-flow in a
ventilated enclosure on page 14.
Total heat dissipation
1.
Add the dissipation figures from step 6 (in Planning the installation)
for each drive that is to be installed in the enclosure. Make a note of
the total value.
2.
If an RFI filter is to be used with each drive, add the dissipation
figures from step 29 (in EMC emission standards – instructions later
in this chapter) for each RFI filter that is to be installed in the
enclosure. Make a note of the total value.
3.
If the braking resistor is to be mounted inside the enclosure, add the
average power dissipation from step 12 (in Planning the installation)
for each braking resistor that is to be installed in the enclosure. Make
a note of the total value.
4.
Make a note of the total heat dissipation (in Watts) of any other
equipment to be installed in the enclosure.
5.
Add the heat dissipation figures obtained (as appropriate) from lines
1, 2, 3 and 4 above. This gives a figure in Watts for the total heat that
will be dissipated inside the enclosure. Make a note of this figure.
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
(1m
2
= 10.8ft
2
)
T
amb
Maximum expected ambient temperature in °C outside the
enclosure
T
i
Maximum intended ambient temperature in °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
/°C
Take care when performing these calculations in order to ensure
the ambient temperature inside the enclosure does not exceed
55°C (131°F) or 45°C (113°F), as appropriate (see step 6 in Planning
the installation).
Example
To calculate the size of an enclosure for the following:
•
Three M’Ax 409
•
Each drive is to have an external braking resistor mounted inside the
enclosure
•
An RFI filter (model 3258-16-45) to be used with each drive
•
Maximum ambient temperature inside the enclosure: 55°C
•
Maximum ambient temperature outside the enclosure: 30°C
Dissipation of the drive: 180W (from section 2.11 Output current,
Ambient temperature, Heat dissipation, De-rating on page 7)
Average dissipation from the braking resistor: 171W (from section
2.18 Minimum permissible deceleration time on page 10)
Dissipation of each RFI filter: 6W (max) (from Installing an RFI filter on
page 21
Total dissipation: 3 x (180 + 171 + 6) = 1071W
The enclosure is to be made from painted 2mm (0.0787in) sheet steel
having a heat transmission coefficient k of 5.5W/m
2
/°C. Only the top,
front, and two sides of the enclosure are to be free to dissipate heat.
A
e
P
k T
i
T
amb
–
(
)
---------------------------------
=
NOTE
