Rockwell Automation DeviceNet Media Design Installation Guide - Manual (Page 100)

Publication DNET-UM072C-EN-P - July 2004
4-22 Determine Power Requirements
One power supply (end-connected)
Example using thick cable
The following example uses the full calculation method to determine the
configuration for one end-connected power supply on a thick cable trunk line.
• Device 1 and Device 2 cause the same voltage drop but Device 2 is
twice as far from the power supply and draws half as much current.
• Device 4 draws the least amount of current but it is furthest from the
power supply and causes the greatest incremental voltage drop.
1. Find the voltages for each device using the equation for thick cable.
SUM {[(L
n
x (0.0045)) + (N
t
x (0.005))] x I
n
} < 4.65V.
A.[(50 x (0.0045)) + (1 x (0.005))] x 1.00 = 0.23V
B.[(100 x (0.0045)) + (2 x (0.005))] x 0.50 = 0.23V
C.[(400 x (0.0045)) + (3 x (0.005))] x 0.50 = 0.91V
D.[(800 x (0.0045)) + (4 x (0.005))] x 0.25 = 0.91V
2. Add each device’s voltage together to find the total voltage.
0.23V + 0.23V + 0.91V + 0.91V = 2.28V
Since the total voltage does not exceed 4.65V, the system will operate properly
(2.28V < 4.65V).
The percent loading is found by dividing the total voltage by 4.65V.
%Loading = 2.28/4.65 = 49%
power
supply
PT TR TR T T T T
D1 D2 D3
15 m
(50 ft)
30 m
(100 ft)
122 m
(400 ft)
244 m
(800 ft)
1.0A 0.50A 0.50A
D4
0.25A
TR = terminating resistor T = T-Port tap
PT = Power Tap D = device
31514-M
D1
1.0A
D2
0.50A
D3
0.50A
D4
0.25A
Results