Plexlog Plexlog (grid)
The Plexlog energy manager is a PV monitoring and energy management system that aggregates data from inverters, meters, and other devices at a site. This Modbus TCP template reads per-phase active power at the grid connection point: phase A (L1), phase B (L2), and phase C (L3), each as a signed 32-bit integer via function code 4. Connecting the Plexlog Open Gateway to ModbusCloud lets installers and asset managers track live grid power flow across all three phases in a single dashboard view.
- Protocol
- Modbus TCP
- Connection
- Ethernet, Modbus TCP
- Registers
- 3, read only
- Brand
- Plexlog
- Last updated
Registers (3)
3 read, 0 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| power_a | W | Read | |||
| power_b | W | Read | |||
| power_c | W | Read |
Loading registers…
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Use cases
- Monitor per-phase active power at the grid connection point to detect phase imbalances in real time.
- Track live import and export values on L1, L2, and L3 to verify correct meter wiring after installation.
- Alert on sustained high import on a single phase to identify unbalanced load distribution at the site.
- Compare per-phase grid power trends over time to support capacity planning and tariff optimisation reviews.
- Verify that feed-in limiting is operating correctly by checking that all three phase readings stay within allowed thresholds.
Installation
Enable the Modbus TCP Open Gateway on the Plexlog energy manager: contact Plexlog to activate the Open Gateway feature, then confirm the TCP port (default 502 or 503 depending on firmware) and Unit ID (default 1) in the device settings.
Connect the Plexlog energy manager to the same LAN as the ModbusCloud Gateway, ensuring both devices share the same IP subnet and there are no firewall rules blocking the configured Modbus TCP port.
In the ModbusCloud portal, add a new device, import the Plexlog (grid) template, and enter the Plexlog IP address, port, and Unit ID (typically 1) to complete the connection profile.
Spot-check the three phase registers (power_a at address 0, power_b at address 2, power_c at address 37) in the portal's live register view and confirm values match the readings shown on the Plexlog local interface or a reference meter.
Things to watch for
All three phase registers return zero or no value. Why?
The Plexlog Open Gateway only exposes grid connection point values when a compatible grid analyser or meter is integrated and actively communicating within the Plexlog system. Verify the meter is correctly configured and showing live data in the Plexlog local interface before polling via Modbus TCP.
Function code 4 returns an exception error. What is wrong?
The Plexlog Open Gateway requires function code 4 (Read Input Registers) for these registers. Using function code 3 (Read Holding Registers) will return an illegal function exception. Confirm your polling tool or gateway configuration is set to function code 4, matching the template definition.
The gateway connects but the phase power values look incorrect or byte-swapped.
The Plexlog Open Gateway uses Big Endian byte order for 32-bit registers. Each register spans two consecutive 16-bit words. If your client reads the word order incorrectly, values will appear byte-swapped or nonsensical. Ensure your Modbus client is configured for Big Endian 32-bit integer decoding.
The Plexlog IP is reachable but Modbus TCP connections are refused.
The Modbus TCP Open Gateway on the Plexlog is not enabled by default and must be activated by Plexlog support. Also confirm which port is active on your firmware version: port 502 is documented as the standard port, while port 503 is used on some configurations. Check the Plexlog firewall settings and ensure the correct port is open on any intermediate network equipment.
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