Chapter 11 Installation and Wiring
11-2
The following shows the method to calculate the current consumption of PLC system itself necessary for heat
protection design.
4) Current Consumption Block Diagram of PLC System
5) Current Consumption of Each Part
(1) Current Consumption of Power Module
Current conversion efficiency of power module is about 70% and 30% is consumed by the
radiation, and 3/7 of output power shall be a current consumption itself. Accordingly, the
calculation formula is as below.
•
W
pw
= 3/7 {(I
5V
X 5) + (I
24V
X 24)} (W)
I
5V
: Current consumption of DC5V circuit of each module
(internal current consumption)
I
24V
: Average current consumption of DC24V of output module
(current consumption of simultaneous On point)
Not available in case that DC24V is supplied from outside or power module
without DC24V output is used.
(2) Sum of DC5V circuit current consumption
DC5V output circuit current of power module is the sum of current consumption of each
module.
•
W
5V
= I
5V
X 5 (W)
(3) DC24V Average current consumption (current consumption of simultaneous On point)
DC24V output circuit average current of power module is the sum of current consumption of
each module.
•
W
24V
= I
24V
X 24 (W)
(4)
Average current consumption by output voltage drop of output module
(current consumption of simultaneous On
point)
•
W
out
= I
out
X V
drop
X output point X simultaneous On rate (W)
I
out
: output current (current in actual use) (A)
V
drop
: voltage drop of each output module (V)
Power
CPU
Constant
voltage
transformer
AC power
100V~240V
COM. COM. OUT IN
SPE
DC5
DC24
Load
I
out
I
in
I
5V
I
24V
AC power
100V~240V
DC
power
24V