Mitsubishi A2USCPU(S1), User Manual

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8. LOADING AND INSTALLATION
8.3 Calculation Method of Heat Amount Generated by the PLC
It is necessary to keep the temperature of the panel which stores the PLC to the operating
ambient temperature of the PLC, which is 55
, or below. For heat dissipation design of
the panel, it is necessary to know the average power consumption (heat generation) of the
devices and machinery stored inside. In this section, a method to obtain the average
power consumption of the PLC system is explained. Calculate the temperature rise inside
the panel from the power consumption.
(Calculation method of average power consumption)
The power consuming parts of the PLC may be roughly classified into the blocks as shown
below:
(1) Power consumption by power supply module
The power conversion efficiency of the power supply module is about 70%, and 30%
is consumed as heat generated, thus, 3/7 of the output power is the power
consumption. Therefore, the calculation formula is:
Wpw= {(I
5V
5) + (I
15V
15) + (I
24V
24)}(W)
(Current consumption equivalent to the points simultaneously ON)
Not applicable to a system where 24VDC is supplied externally and a power
supply module which does not have a 24VDC output is used.
(2) Total power consumption of each module at 5VDC logic part
Power of the 5VDC output circuit of the power supply module is the power
consumption of each module.
W
5V
=I
5V
5(W)
I
5V
: Current consumption of 5VDC logic circuit of each module
I
15V
: Current consumption of 15VDC external power supply part of special function
module
I
24V
: Average current consumption of 24VDC power supply for internal consumption
of the output module
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