User`s guide

Appendix B - Adept DeviceNet
94 Adept SmartController User’s Guide, Rev. K
Power Supply and the DeviceNet Bus
The DeviceNet network allows distribution of power supplies on the network cable
system. Follow these general rules to achieve safe and reliable operation:
• Use power supplies rated at 24 V
• Minimize installation problems by using a single power supply with
sufficient current to operate all the attached nodes. This must comply with
national and international safety standards.
• Make sure that each power supply incorporates current-limit protection.
• Make sure each power supply is temperature compensated.
• Provide over-current protection for each segment of your DeviceNet cable
installation.
NOTE: Adept does not supply the 24 V operating voltage for the
DeviceNet bus on the SmartController or any other Adept component.
Power Capabilities of a DeviceNet Cable System
A DeviceNet cable system has several power rating constraints. The cable type and the
length of the cable specify the maximum current on a cable. Thick and thin cable have:
• 24 VDC power rating
• Optional power-supply tabs
If the power supplies are equipped with Schottky diodes, the optional power supply tabs
must be protected from bus back-feeding of current among the power supplies on the bus.
We also recommended the use of fuse protection for every trunkline in the cable system.
The maximum current rating of a thick cable trunk line is 8 A.Verify that this complies
with your national and international standards. It might be necessary to limit the
maximum current to a lower value if standards in the U.S. or Canada apply. The
maximum current value is a theoretical value. The cable size supports a higher current
than 8 A. Depending on the topology of nodes relative to the power supply, higher
currents might be possible. See the DeviceNet technical specifications for further
information.
The maximum current rating of a thin cable trunk line is 3 A. If you use the thin cable on a
long line, the resistance of the cable decreases the maximum current value. See Table B - 5
and the DeviceNet technical specifications for further information.
WARNING: The DeviceNet specification requires that the
CAN_H and CAN_L signal lines tolerate voltages up to
18 V. Since the supply voltage exceeds 18 V, improperly
wiring the supply voltage to these signal lines may cause
equipment damage.