Calculating Heat Generated By A173Uhcpu/A172Shcpun/A171Shcpun - Mitsubishi Electric A173UHCPU User Manual

2. DESIGN

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.
I
CPU
AC
(power
power
supply)
supply
module
I
24V
Exaternal
24 VDC
power supply
(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:
3
Wpw = {(I 5) + (I
5V
7
I :I is the current consumption of the 5 VDC logic circuits of each module
5V 5V
I :I is the 24 VDC average current consumption of the power supply for
24V 24V
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.
= I
W 5(W)
5V 5V
(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.
= I
W 24(W)
24V 24V
5VDC line
5V
Output module
Relay transistor
24VDC line
Output current
(I ) Vdrop
OUT
AC
DC
24)}(W)
24V
2 − 20
Special-function
Input module
Input current
(I ) E
IN
Input
power
Output supply
(I )
power
IN
AC E
supply
(I )
OUT
LOAD
DC
module
Power supply
AC
DC