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2. DESIGN
2
−
20
2.4.4 Calculating Heat Generated by A173UHCPU/A172SHCPUN/A171SHCPUN
If a motion controller is installed in an enclosure, the temperature inside the
enclosure must be restricted to the operation ambient temperature of 55
C
.
The average power consumption (heat generation) of the equipment and
instruments in the enclosure must be known to design the heat dissipation of the
enclosure.
This section describes how to calculate the motion controller system power losses
and average power consumption. Calculate the temperature rise in the enclosure
from the power consumption.
Calculating Average Power Consumption
The major motion controller parts consuming power are shown in the block
diagram below.
AC
power
supply
Exaternal
24 VDC
power supply
24VDC line
5VDC line
Output module
Relay transistor
Output current
(I
OUT
) Vdrop
Input module
Input current
(I
IN
) E
Special-function
module
Power supply
Output
power
supply
(I
OUT
)
LOAD
Input
power
supply
(I
IN
)
AC
DC
E
I
24V
I
5V
CPU
(power
supply)
module
AC
DC
AC
DC
(1) Power consumption of power supply module
The power conversion efficiency of a power supply module is approximately
70%, with the remaining 30% consumed in heat generation.
Therefore, the heat generation is 3/7 of the output power, calculated by the
following equation:
Wpw = {(I
5V
5) + (I
24V
24)}(W)
3
7
I
5V
:I
5V
is the current consumption of the 5 VDC logic circuits of each module
I
24V
:I
24V
is the 24 VDC average current consumption of the power supply for
output module internal consumption
(current consumption of simultaneously ON points)
(2) Total power consumption of 5 VDC logic circuits of all modules
The CPU power supply 5 VDC output circuit power is the total power
consumption of each module.
W
5V
=
I
5V
5(W)
(3) Output module average power consumption (power consumption of
simultaneously ON points)
The CPU power supply 24 VDC output circuit average power is the total power
consumption of each module.
W
24V
=
I
24V
24(W)