Appendix 10 Calculating Heat Generation Of Programmable Controller - Mitsubishi Electric Q26UD(E)HCPU User Manual

Appendix 10
The ambient temperature inside the panel storing the programmable controller must be suppressed to an ambient
temperature of 55°C or less, which is specified for the programmable controller.
For the design of a heat releasing panel, it is necessary to know the average power consumption (heating value) of the
devices and instruments stored inside.
Here the method of obtaining the average power consumption of the programmable controller system is described.
From the power consumption, calculate a rise in ambient temperature inside the panel.
The power consuming parts of the programmable controller are roughly classified into six blocks as shown below.
(1) Power consumption of power supply module
The power conversion efficiency of the power supply module is approx. 70 %, while 30 % of the output power is
consumed as heat. As a result, 3/7 of the output power is the power consumption.
Therefore the calculation formula is as follows.
3
W = × {(I
PW
7
I : Current consumption of logic 5VDC circuit of each module
5V
I : Current consumption of 15VDC external power supply part of intelligent function module
15V
I : Average current consumption of 24VDC power supply for internal consumption of the output module
24V
In a redundant power supply system, the same calculation method is applied.
(When 2 redundant power supply modules are placed in parallel, they run sharing the load current half-and-half.)
(2) Total power consumption for 5VDC logic circuits of all modules
(including CPU module)
The power consumption of the 5VDC output circuit section of the power supply module is the power consumption
of each module
W = I × 5 (W)
5V 5V
*1 For the power consumption of the motion CPU and PC CPU module, refer to the user's manuals of the corresponding
modules.
(3) Total of 24 VDC average power consumption of the output module
(power consumption for simultaneous ON points)
The average power of the 24VDC external power supply is the total power consumption of each module.
W = I × 24 × Simultaneous ON rate (W)
24V 24V
674
Calculating Heat Generation of Programmable
Controller
How to calculate average power consumption
×5) + (I ×15) + (I
5V 15V 24V
*1
. (The current consumption of the base unit is included.)
×24)} (W)