Calculating Heat Generation By Unit - Mitsubishi MELESEC-ST User Manual

10 MOUNTING AND INSTALLATION

10.5 Calculating Heat Generation by unit

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The ambient temperature inside the control panel storing the MELSEC-ST system
must be suppressed to the MELSEC-ST system operating ambient temperature of
55°C.
When designing control panel to radiate heat, it is required to obtain the average power
consumption (heating value) of the devices and instruments to be stored within the
control panel.
This section explains how to obtain the average power consumption of the MELSEC-
ST system. Based on the power consumption, calculate a rise in ambient temperature
inside the control panel.
How to calculate average power consumption
The power consuming sections of the MELSEC-ST system are roughly classified into
six blocks as shown below.
(1) Power consumption of bus refreshing module
The power conversion efficiency of the bus refreshing module is approx. 80 %,
i.e., 20 % of the power is consumed by heating. As a result, 2/8 of the output
power becomes the power consumption.
Therefore the calculation formula is as follows.
2
Wpw = I
5V
8
I : 5VDC internal current consumption of each slice module
5V
(2) Total power consumption of 5VDC circuit section for slice modules
and head module
The power consumption of the 5VDC circuit section of slice modules (except the
bus refreshing module) and head module is the total power consumption of these
modules.
W = I 5 (W)
5V 5V
(3) Total power consumption of 24VDC power supply section for output
modules
(power consumption for simultaneous ON points)
The average power of the external AUX. power supply is the total power
consumption of the output modules.
W = I 24 (W)
24V 24V
I 24VDC
24V:
(4) Average power consumption due to voltage drop in the output
section of the output module
(Power consumption for simultaneous ON points)
W = I Vdrop
OUT OUT
I : Output current (Current in actual use) (A)
OUT
Vdrop : Voltage drop in each output module (V)
(5) Average power consumption of the input section of the input
module(Power consumption for simultaneous ON points)
W = I E
IN IN
I : Input current (A)
IN
E : Input voltage (Voltage in actual use) (V)
5 (W)
Number of outputs
Number of input points
MELSEC-ST
Simultaneous ON rate (W)
Simultaneous ON rate (W)
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