Vacon 20 CP, Installation, Technical And Maintenance Manual

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Mounting vacon • 30
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3
3.7 Dimensioning an external heatsink
This paragraph describes a useful procedure to select a suitable heatsink for VACON
®
20 CP
drives.
The heatsinks are devices that enhance heat dissipation from a hot surface, usually the case
of a heat generating component, to a cooler ambient, usually air. For the following discussion,
air is assumed to be the cooling fluid. The primary purpose of a heatsink is to maintain the de-
vice temperature below the maximum allowable specified by the device manufacturers. Before
discussing the heatsink selection process, it’s necessary to define common terms, notations
and definitions and establish the concept of a thermal circuit.
Notations and definitions of the terms are as follows:
The purpose of this paragraph is to select an external heatsink by calculating its thermal re-
sistance.
The heat transfer principle from the cold plate to the heatsink ambient air is shown in Figure
15.
Figure 15.Thermal equivalent circuit.
Symbol Description
CP
loss
Cold plate loss: see Table 8, Table 9 or Table 10 expressed in W
T
CPmax
Maximum cold plate temperature expressed in °K (358 °K = 85°C)
T
amb
heatsink ambient temperature expressed in °K(°K = °C + 273)
R
CP
Equivalent thermal resistance [K/W] of the cold plate.
R
HSmax
Thermal resistance of the heatsink [K/W]
Table 11. Terms and definitions for the thermal model.
CP
loss
T
amb
R
CP
R
HS
T
CP
T
CP
T
amb
T
Enclosure