24 V dc power with Ethernet specification

Like a round peg in a square hole, end-users can face incompatibility when designing and deploying 24 V auxiliary power on the factory floor. In response, ODVA is creating a "Power with Ethernet" specification for ODVA's networks based on Common Industrial Protocol (CIP). The 24 V dc auxiliary power specification is expected this month. Link to separate Power over Ethernet Plus information.

By Mark T. Hoske, Control Engineering April 8, 2009
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More from ODVA. Also see the separate IEEE Power over Ethernet Plus for factory automation. Add your comments.

Like a round peg in a square hole, end-users can face incompatibility when designing and deploying 24 V auxiliary power on the factory floor. In response, ODVA is creating a “Power with Ethernet” specification for ODVA’s networks based on Common Industrial Protocol (CIP). The 24 V dc auxiliary power specification is expected this month, according to reports made at the 2009 CIP Networks Conference & 13th Annual Meeting, Feb. 24–26.

The 24 V dc output power from an EtherNet/IP compatible device would run in a separate cable from the cable used for Ethernet data (as opposed to the IEEE Power over Ethernet, PoE, specification, which goes through the same wires), says Bob Lounsbury, chair for the ODVA EtherNet/IP Physical Layer Special Interest Group (SIG).

Total current in the system, as seen by power supply PS1, is the sum of the currents at each device (load): ltotal = IL1 + IL2 + IL3.

The power (actually 18–24 V dc depending on distance from the source) would operate e-stops, I/O sources and devices, actuators, and controllers—all of which may need more power than PoE or PoE-Plus wire can deliver, explains Lounsbury, who is also a principal engineer at Rockwell Automation. Work on the specification has involved several ODVA CIP groups, including the DeviceNet Physical Layer SIG. That group began considering 24 V dc power for CIP devices five years ago, covering topology, cable, and connectors. (The system is designed to provide no less than 18 V dc.)

Among details expected in the specification are support for:

  • Star, linear, and daisy chain topologies;

  • 4-pin mini and micro connectors; and

  • 5-pin IP67 connectors (compatible with Profibus).

Safety also is being considered, Lounsbury says, by ensuring male pins wouldn’t be exposed, and trying to make sure damage wouldn’t occur if cables were accidently plugged in where they shouldn’t be.

Also read: Power over Ethernet Plus for factory automation . Have you looked at PoE and Power with Ethernet? Which is better for what? Share your views and experiences using the posting TalkBack tool below.
For other recent ODVA coverage, see:

10 benefits of Common Industrial Protocol networks, according to ODVA

; and

Testing, time-based control help CIP based networks; ODVA meets Feb. 24-26

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Author Information
Mark T. Hoske is Control Engineering editor in chief. Reach him at MHoske@cfemedia.com .