Connecting Two Eastron Meters to a Sunsynk or Deye Inverter

Key Takeaways

• In AC-coupled solar systems, two Eastron meters can be integrated into a single RS485 meter port on Sunsynk and Deye inverters to monitor grid exchange and string PV production.
• If the hybrid inverter is located 10 or more meters away from the incoming supply, an external Eastron meter must replace standard analogue CT leads.
• Both meters must share the identical make and model, with the Eastron SDM630CT recommended for unlocked front-panel configuration.
• Modbus slave addresses must be programmed strictly: Address 1 for grid monitoring and Address 2 for string PV generation.
• Before modifying electrical connections, isolate main AC circuit breakers and follow safe working procedures in accordance with national wiring standards.

Architecture of Dual-Meter AC-Coupled Solar Systems

As solar installations throughout South Africa expand from simple residential backup systems into high-capacity commercial microgrids, AC-coupling has emerged as a preferred retrofit architecture. In many commercial facilities, farms, and larger residences, an existing grid-tied string inverter (such as a Fronius, SMA, or Sungrow unit) already generates solar power on the main distribution board. Rather than replacing functional grid-tied inverters, installers deploy a Sunsynk or Deye hybrid inverter alongside lithium battery storage to provide load-shedding resilience and self-consumption optimization.

Managing an AC-coupled plant requires complete bidirectional telemetry. The hybrid inverter must simultaneously measure incoming utility power at the main boundary to prevent illegal grid feed-in and monitor active AC generation from the third-party string inverter. While standard installations rely on analogue current transformers, physical layout constraints frequently make analogue wiring impossible. Fortunately, it is possible to use 2 meters connected to the single meter port on the inverter over a shared RS485 serial communication bus.

If using the Sunsynk inverter as an AC coupled battery charger, you may wish to use an Eastron Meter to record PV data from the string inverter for additional monitoring. Without real-time generation telemetry from the PV string inverter, the hybrid inverter cannot determine how much power is available for battery charging versus building consumption, leading to inefficient energy cycling and inaccurate mobile monitoring graphs.

Furthermore, physical distance frequently dictates meter deployment. If the Sunsynk inverter is 10+ meters away from the incoming supply, an Eastron Meter needs to be used in place of the supplied CTs for GRID side AC readings. Extending analogue CT wiring beyond 10 meters exposes low-amplitude current signals to significant electromagnetic interference from adjacent motor circuits, air conditioning units, and heavy industrial plant equipment. Digital RS485 communication eliminates noise vulnerability, delivering clean numerical data packets across long plant room runs.

Meter Selection and Hardware Compatibility

When establishing a multi-drop RS485 network connected to a single serial port on the hybrid inverter, strict hardware consistency is required.

Both meters must be the same make and model. We recommend the Eastron SDM630CT, this is because the device allows the settings changes needed without the need for contacting Eastron for additional equipment and software to change the device settings. Mixing different meter generations causes severe register polling collisions on the Modbus bus. Because different meter models format data across distinct register addresses and register lengths, the hybrid inverter's serial driver cannot query mismatched meters over the same physical communication line.

The Eastron SDM630CT provides an unlocked front-panel configuration menu that allows installers to adjust Modbus slave addresses, baud rates, parity bits, and current transformer transformation ratios directly using navigation buttons, without requiring proprietary optical communication probes or specialized software.

Parallel RS485 Bus Wiring for Multiple Meters

RS485 is a differential serial communication standard designed to support multiple transceiver nodes on a single two-wire bus line arranged in a daisy-chain topology. Star or tee topologies must be strictly avoided, as cable stubs generate high-frequency signal reflections that corrupt data frames.

```
DUAL EASTRON METER DAISY-CHAIN RS485 BUS TOPOLOGY

+--------------------+ +--------------------+
| EASTRON METER 1 | | EASTRON METER 2 |
| (Grid Side) | | (PV Side) |
| Address 1 | | Address 2 |
| [14] [13] | | [14] [13] |
| TX+A TX-B | | TX+A TX-B |
+----|-----------|---+ +----|-----------|---+
| | | |
=====+===========+===============+===========+===== RS485 Bus
| | |
| | [120 Ohm] End-of-Line
| | Resistor (Optional)
+----|-----------|---+
| Pin 5 Pin 4|
| (485-A) (485-B|
| INVERTER RJ45 |
| Meter Port |
+--------------------+
```

Cabling and Terminal Connections

1. Use high-grade Cat5e or Cat6 shielded twisted-pair (STP) cable.
2. Designate a single twisted pair for differential data transmission (for example, Blue for A and Blue/White for B).
3. Connect the Blue conductor (Data +) to terminal 14 (TX+A) on Meter 1, and loop it directly onward to terminal 14 (TX+A) on Meter 2.
4. Connect the Blue/White conductor (Data -) to terminal 13 (TX-B) on Meter 1, and loop it directly onward to terminal 13 (TX-B) on Meter 2.
5. Route the primary incoming trunk from Meter 1 back to the hybrid inverter. Terminate the twisted pair into a standard RJ45 modular connector where Pin 5 connects to TX+A (485-A) and Pin 4 connects to TX-B (485-B).
6. Insert the crimped RJ45 plug into the port designated Meter or RS485 on the inverter base plate.

To maintain signal integrity across long electrical runs, connect the bare shielding drain wire to the earth busbar inside the main distribution board only. Never ground both ends of the communication shield, as circulating ground currents induce common-mode noise.

Modbus Address Programming and Serial Parameters

Because both meters share the same physical pair of communication wires, the hybrid inverter differentiates between grid boundary data and solar generation data using unique numerical Modbus slave device addresses.

```
+------------------+---------------------+---------------------+

+------------------+---------------------+---------------------+

+------------------+---------------------+---------------------+
```

Programming Meter 1 (Grid Monitoring)

1. Energize the auxiliary voltage terminals on Meter 1.
2. Press and hold the navigation button on the front panel for 3 seconds until the password prompt appears.
3. Enter the default security password 1000.
4. Navigate to the address parameter screen. The grid meter Modbus address must be set to 1.
5. Set the communication baud rate to 9600 bps.
6. Verify parity is set to None with 1 stop bit.
7. Program the primary and secondary CT ratings (e.g. 100/5A or 200/5A) matching the physical clamps installed on the main incoming utility phase cables.

Programming Meter 2 (PV Generation Monitoring)

1. Energize the auxiliary voltage terminals on Meter 2.
2. Access the programming menu by holding the navigation button for 3 seconds and entering password 1000.
3. Navigate to the address parameter screen. The PV meter Modbus address must be set to 2.
4. Set the communication baud rate to 9600 bps, ensuring identical transmission timing with Meter 1.
5. Confirm parity is configured as None with 1 stop bit.
6. Program the CT transformation ratios matching the current transformers clamped over the output phase lines of the third-party string inverter.

Specialized Firmware Requirements and Support Escalation

Standard factory firmware releases on Sunsynk and Deye inverters are configured to poll only a single external meter at Modbus address 1. When a technician connects a second meter without updating the system software, the inverter processor ignores data packets transmitted by address 2.

The inverter must be updated to a specialised software version for this compatibility. Please contact Sunsynk Support for this update specifying that the software needs to allow Grid Meter 2 to be enabled.

When opening a support escalation or service ticket with Sunsynk or Deye technical support in South Africa, provide:

• The exact inverter serial number (located on the side chassis barcode sticker).
• The current main control board (HMI) and communications processor firmware revisions (viewable under the system information screen).
• Clear specification that the system is an AC-coupled microgrid requiring dual-meter Modbus support for Grid Tie Meter 2.

Technical support engineers push the specialized software update over-the-air (OTA) via the connected Wi-Fi or 4G data logger. Once the flashing procedure completes, the advanced settings menu unlocks the necessary configuration toggles.

Inverter Advanced Menu Settings and Commissioning

Once the specialized firmware update is installed and both Eastron meters are wired on the RS485 bus, finalize system commissioning through the inverter touchscreen:

1. Wake the touchscreen and access the technical configuration portal by entering the administrative pin code.
2. Navigate to Settings > Advanced Settings > Others.
3. Once both meters are connected, Ex_Meter for CT and Grid Tie Meter 2 must be enabled in the inverter settings, and the meter type must be set to Eastron .
4. Save the configuration. The inverter processor reinitializes its RS485 polling routine, cycling requests between Modbus address 1 and Modbus address 2 every 500 milliseconds.

```
ADVANCED SETTINGS -> OTHERS CONFIGURATION
+-------------------------------------------------------+
| [X] Ex_Meter for CT Meter Select: [Eastron] |
| [X] Grid Tie Meter 2 Baud Rate: [9600] |
| |
| Modbus Polling: |
| Address 1 -> Grid Boundary Active Power |
| Address 2 -> External String Inverter AC Power |
+-------------------------------------------------------+
```

Verification and Telemetry Validation

Confirm system stability by observing operational parameters across diverse operating states:

• Grid Telemetry Verification: Observe the main screen. When household loads draw power from the utility grid, the grid power reading should match the active power displayed on Meter 1.
• PV Telemetry Verification: Check the solar generation screen. The inverter should now display an active Grid-Tie Inverter power block displaying kilowatts generated by the third-party string inverter, perfectly tracking the display on Meter 2.
• Battery Charging Coordination: In the presence of excess generation from the string inverter, the hybrid inverter should automatically modulate its AC battery charger, absorbing surplus energy to recharge the lithium battery bank without tripping municipal anti-feed-in relays.

By deploying matched Eastron SDM630CT meters over an isolated RS485 daisy-chain and applying specialized multi-meter firmware, South African solar engineers can successfully integrate high-performance AC-coupled storage systems into complex commercial and residential electrical installations.