8
Thermal constrains
This device must be correctly heatsinked for proper and
reliable operation.
The built-in fans and an appropriate external passive
heat sink guarantee by design thermal efficiency and
reliability.
Proper heat sink planarity is strongly suggested to allow
thermal transfer from the module’s bottom plate to the
heatsink; a thermal compound may be used, but it is not
strictly necessary.
In order to ensure proper ventilation of the module,
reasonable spacing of at least 100 mm must be left between
the frame of the unit and any side component or surface of
the enclosure.
The module has been designed to fit into a loudspeaker
cabinet: please refer to
for proper module placing.
IN
HEATSINK FINS ARE SET HORIZONTALLY
(WRONG!) ONLY FOR DESCRIPTIVE PURPOSE.
We suggest to position the module vertically with respect
the ground in order to take advantage of the chimney effect
for ventilation and heat dissipation.
A custom heat sink designed to best fit the M-Drive is
available: please refer to the M-Drive IK solution for more
info on this subject.
8 : 1.Heatsink performance
Here we suggest a rule of thumb to calculate the thermal
resistance of the heatsink.
The absolute thermal resistance of the heatsink is
the temperature difference (kelvin or celsius) across it
structure when a unit of heat energy flows through it in
unit time (watt). For seek of simplicity, a heatsink with low
thermal resistance offers high heat dissipation, as well as
a low electric resistance allows high current flow through a
conductive wire.
In order to define the maximum allowed thermal
resistance for the heatsink let assume the following:
f
f
e
as the amp module efficiency
f
f
cf
as the crest factor of the audio signal
f
f
W
max
as the peak power delivered by the module
f
f
T
amb
as the highest ambient temperature
f
f
T
mod
as the highest operating temperature
The thermal resistance of the heatsink derives from the fol-
lowing formula:
and 3400 W peak power, the dissipated heat is:
Considering that thermal protection of the module (
T
mod
) is
set at 75°C (167°F) on the bottom aluminium plate and stat-
ing an ambient temperature of 45 °C (113°F), the previous
The maximum dissipated power can be calculated as:
For example, stating an efficiency of 80%, 6 dB crest factor
8 : 2.Suggested heatsink
Powersoft provides a M-Drive compatible heat sink,
specifically designed to house the amp module, an input/
output interface and the AC mains connection: please refer
to the M-Drive IK solution for more info on this subject.
example gives:
meaning that the temperature of the bottom plate is always
lower than 75°C if the heatsink has a thermal resistance bet-
ter than 0.14°C/W (or 0.14 K/W) with ambient temperature
up to 45 °C.
100 mm
3.94 inch MIN.
Do not obstruct
air flow
Fans side
Fans side
FIGURE 1: Cooling solutions (for descriptive
purpose the heatsink fins are set in wrong direc-
tion): module in a separate vented chamber.
Dissipated power
=
cf
W
max
(1 -
e
)
R
th
=
Dissipated power
T
mod
-
T
amb
= 0.14°C/W
170
75 - 45
= 170 W
4
3400 (1 - 0.8)
2 | M-Drive | User guide
