Parker H Series, Installation & Service Instructions Manual

Page: 162 / 344

Publication DNET-UM072C-EN-P - July 2004
1-18 Get Started
Power supply 2
Add each device’s (D3, D4, D5) current together for power supply 2
( 0.25+1.00+0.10=1.35A ).
1.35A is the minimum name-plate current rating that power supply 2 should
have. Remember to consider any temperature or environmental derating
recommended by the manufacturer.
Place the power supply
DeviceNet networks with long trunk lines or with devices on them that draw
large currents at a long distance sometimes experience difficulty with common
mode voltage. If the voltage on the black V- conductor differs by more than 4.65
volts from one point on the network to another, communication problems can
occur. Moreover, if the voltage between the black V- conductor and the red V+
conductor ever falls below 15 volts, then common mode voltage could adversely
affect network communication. To work around these difficulties, add an
additional power supply or move an existing power supply closer to the heavier
current loads.
If possible, power supplies should be located at the middle of the network to
shorten the distance from the power supply to the end of the network.
To determine if you have adequate power for the devices in your cable system,
use the look-up method which we describe more fully in Chapter 4. See the
following example and figure (other examples follow in Chapter 4). You have
enough power if the total load does not exceed the value shown by the curve or
the table.
In a worst-case scenario, all of the nodes are assumed to be together at the
opposite end of the power supply, which draws all current over the longest
distance.
IMPORTANT
This method may underestimate the total current capacity
of your network by as much as 4 to 1. See Chapter 4 to use
the full-calculation method if your supply does not fit
under the curve.
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