6 Selecting an External Heatsink
YASKAWA ELECTRIC
TOBP C710606 40A YASKAWA AC Drive - J1000 Finless Installation Manual
23
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Heatsink Selection by Thermal Resistance
Substituting the example values into the formula gives:
The heatsink must have a thermal resistance lower than 1.7 K/W. When selecting the
heatsink apply a safety margin to the calculated value in order to ensure tripless drive
operation, even if the installation conditions change (temporary higher temperature, loss of
cooling ability of the external heatsink due to dust, etc.).
■
Feasibility Check of a Selected Heatsink
If for example a heatsink with R
θ
EHS
= 1.6 K/W is selected, the heatsink temperature will be:
The selected heatsink can be used, but considering that the heatsink area is probably larger
than the drive footprint and the ambient conditions could change (reduced heatsink cooling
ability by dirt, etc.), a heatsink with a lower R
θ
EHS
(e.g. R
θ
EHS
= 1.1 K/W, resulting in T
HSP
= 72.2ºC) should be chosen.
R
θ
EHS_max
=
90
͠
- 40
͠
27.5 W
- 0.05 K/W - 0.02 K/W
(
)
=
1.74 K/W
T
HSP
= 27.5 W
0.05 K/W + 0.02 K/W
+ 1.6 K/W) + 40
͠
=
85.9
͠