Network Power Supply Unit Position And Current Capacity Calculation - Mitsubishi Electric QJ71DN91 User Manual

5 SETUP AND PREPARATION

5.7.2 Network power supply unit position and current capacity calculation

Network power
supply unit
Terminating
resistor
Terminating
resistor
Master node
0.1A
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This section describes where to install the network power supply unit and how to
calculate the current capacity.
(1) Connecting the network power supply unit to one end of the network
When the network is 200m long in total and uses thick cables, the current
capacity can be calculated as shown below.
Master node Slave node
0.1A 0.15A
Total power supply distance = 200m
Total current capacity = 0.1A + 0.15 + 0.05A + 0.25A + 0.1A = 0.65A
Max. current capacity available for total thick cable length of 200m (See Table
5.4.) = 1.53A
Therefore, this configuration allows power supply to all nodes.
(2) Connecting the network power supply unit to the center of the
network
When the network uses thick cables, the current capacity can be calculated as
shown below.
In this case, the network power supply unit can supply twice the current
compared to when it is connected to the end of the network.
Slave node Slave node
0.25A 0.2A
120m
Power supply distance on the left side = Power supply distance on the right side
= 120m
Total current capacity of the left side = 0.1A + 0.25A + 0.2A = 0.55A
Total current capacity of the right side = 0.15A + 0.25A + 0.15A = 0.55A
Max. current capacity available for thick cable length of 120m (See Table 5.4.) =
approx. 2.56A
(Straight-line approximation between 100m and 150m)
Therefore, this configuration allows power supply to all nodes.
Slave node Slave node
0.05A
200m
Network power
supply unit
Slave node
0.15A
Slave node
0.25A 0.1A
Slave node Slave node
0.25A 0.15A
120m
MELSEC-Q
Terminating
resistor
Terminating
resistor
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