Modbus RTU 485

Many leading generator manufactures are equipped with a Modbus RTU 485 interface. This interface will connect to Critical Labs using the method below.

Hardware Requirements

  • Verify the generator controller supports a Modbus RTU 485 connection. 
  • Critical Labs Modbus RTU to Modbus TCP converter is needed to convert the slower RTU 485 signal to the faster Modbus TCP signal.    The Critical Labs converter auto translates Modbus RTU to Modbus TCP without additional programming of Modbus registers. Typically the Modbus converter is installed in the generator control panel or the Automatic Transfer Switch (ATS).

Cable Requirements

  • Cat 5/6 cable from the IT network to the Critical Labs Modbus RTU 485 to Modbus TCP converter.
  • A twisted pair shielded cable is to be installed between the generator Modbus RTU 485 interface and the Critical Labs converter.  Cables run under 100 feet use18 gauge conductors.

Power Requirements

  • External power is needed to power the Critical Labs Modbus converter.
    • Option 1 (preferred) – Power from the generator battery circuit by wiring 8-24 volts to the converter screw terminals. 
    • Option 2 (acceptable) Install a PoE to DC power splitter near the Critical Labs converter.  PoE Texas model GBT-12V60W is an example of a splitter.
      • From the PoE IT network switch run a CAT 5 cable to the PoE splitter, plug into the “PoE IN” port on the power splitter.  Run a cable 5 cable from the splitter LAN port to the Ethernet port of the Critical Labs Modbus adapter.  From the 12 VDC screw terminals of the splitter, wire to the Critical Labs adapter.
  • The IT network switch is to be backed up by a battery back up system.   

Generator Programming

  • Program the generator controller to support Modbus 485
    • Set protocol Modbus 485
    • Set Baud Rate to 9600
    • Set 8 None and 1
  • Program Critical Labs Modbus Converter
    • Set IP address
    • Set protocol Modbus 485
    • Set Baud Rate to 9600
    • Set 8 None and 1

Adding to Critical Labs

See our list of articles under Adding a Device to learn how to connect your fully wired and network-connected generator to Critical Labs.

Quick Configuration Checklist

  • Verify generator is capable of Modbus 485
    • If no, select contact closure options
    • If yes, add a Critical Labs Modbus converter
  • Verify Critical Labs gateway is on the customer network
    • if yes, no additional gateway is needed
    • if no, add a Critical Labs gateway and Critical Labs gateway onboarding
  • Verify a Cat 5/6 cable is run between the IT network and the Modbus converter
    • If no, add a Cat 5/6 cable from generator Modbus TCP interface and the IT network
  • Verify a twisted pair shielded cable is run between the IT network and the Modbus converter
    • If no, add a cable from generator Modbus 485 interface and the Modbus converter
  • Add professional services as needed to configure the generator controller and setup Critical Labs software

Quick Scope of Work

  • Critical Labs gateway is a prerequisite and is to be installed on the same network as the generator
  • Generator controller is to support Modbus 485 as a prerequisite, field verify by others
  • Cat 5/6 cable is to be installed from IT network to the Critical Labs Modus converter
  • Twisted pair shielded cable is to be installed from the generator Modbus 485 interface to the Critical Labs Modbus converter
  • External Power from the generator battery is to power the Critical Labs Modbus converter.
  • The generator controller is to be configured by the generator support vendor to support Modbus TCP
  • Program and configure Critical Labs to support generator over Modbus TCP 
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