Plexlog Plexlog (battery)
The Plexlog energy manager (PL40, PL100, PL500+) is a PV and smart-energy monitoring and control device deployed in residential and commercial installations. This ModbusCloud template connects to the Plexlog OpenGateway over Modbus TCP and reads two core battery registers: state of charge and instantaneous power. The signed power value distinguishes charging from discharging in a single field. With these data points in ModbusCloud, operators can track battery behaviour over time, set charge-threshold alerts, and verify that connected storage is performing as expected across all managed sites.
- Protocol
- Modbus TCP
- Connection
- Ethernet, Modbus TCP
- Registers
- 2, read only
- Brand
- Plexlog
- Last updated
Registers (2)
2 read, 0 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| power | W | Read | |||
| soc | % | Read |
Loading registers…
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Use cases
- Monitor battery state of charge continuously to detect abnormal self-discharge between overnight periods.
- Alert on state of charge dropping below a defined threshold during peak-tariff hours.
- Track instantaneous battery power to confirm charge cycles align with PV surplus production windows.
- Compare historical state-of-charge curves across multiple Plexlog sites to spot capacity degradation.
- Verify that the battery shifts from charging to discharging at the expected state-of-charge level each day.
Installation
Enable the Plexlog OpenGateway Modbus TCP interface in the Plexlog portal under the communication or Modbus section, and confirm the target port (typically 502 or 503 as configured on your unit).
Connect the ModbusCloud Gateway to the same LAN as the Plexlog energy manager so that the Gateway can reach the Plexlog IP address on the configured TCP port.
In the ModbusCloud portal, add a new device, import the Plexlog Plexlog (battery) template, and enter the Plexlog unit IP address and the correct Modbus unit ID (usually 1).
Spot-check the soc register (address 36, FC4) in the live register view to confirm a plausible percentage value before saving the configuration.
Things to watch for
The gateway connects but both registers return zero or no data.
Confirm the Modbus TCP port matches exactly what is configured in the Plexlog portal. The OpenGateway may run on port 503 rather than the standard 502. Check firewall or VLAN rules between the ModbusCloud Gateway and the Plexlog unit, and verify the unit ID is set to 1 unless you have changed it.
The power register shows a large unexpected negative value.
The power register at address 37 is a signed int32. A negative value means the battery is currently charging, which is correct behaviour. If the magnitude looks wrong, confirm that no scaling is applied in the template, as the Plexlog OpenGateway delivers watts directly without a divisor.
State of charge reads 65535 or another unrealistic value.
A value of 65535 (0xFFFF) on a uint16 register typically means the Plexlog has not yet associated a battery with this gateway slot, or the battery is offline. Check the Plexlog portal to confirm the storage device is connected and reporting live data internally before polling over Modbus TCP.
Why does function code 3 return an illegal-function exception on these registers?
The Plexlog OpenGateway exposes battery data exclusively on input registers, requiring function code 4. Function code 3 (holding registers) is not supported for these addresses and will return an exception code 1. Ensure the template uses FC4, which is already set correctly in this ModbusCloud template.
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