Teltonika TRB145 – Modbus RTU Communication Issue with Electricity Meter

[Erlandas]

Hello I have a problem.

Equipment:

Teltonika TRB145 (FW: TRB1_R_00.07.12.3)
F&F LE-03MQ CT electricity meter, connected directly via RS485
Modbus RTU protocol
Tested with:
Modbus Poll, QModMaster via RS485–USB – works without issues
Teltonika TRB145 Modbus serial client – When testing Communication Error

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TRB145 Configuration:

RS485: 9600 baud, 8N1, Parity: none, Flow Control: None
Modbus Client Settings:
Slave ID: 3
Function: Read Holding Registers (0x03)
Register Address: 1, Quantity: 2
Data Type: 32-bit float,

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What Has Been Tested?
Communication with the meter verified – RS485–USB works
Tried different register addresses and data types
Disabled Modbus server, using only the client
Teltonika configuration matches the meter parameters

Dont know what to check anymore.
Why is the TRB145 Modbus client unable to read data from the meter while other tools work fine?
How can we debug the Modbus communication on the TRB145?

Thank you for reply.

[Erlandas]

We still have not been able to establish successful communication using the TRB145.

Please provide any insights or suggestions on where else we should look for the issue? Are there any known compatibility concerns or additional debugging steps we could take?

We appreciate your time and support and look forward to your response.

[Martynas]

Hello,

Could you confirm how the wiring communication was verified?

Additionally, if possible, could you try simulating Modbus serial communication using ModRSsim software as described in the wiki example here?

For testing purposes, please also try selecting the default Period value (60) or setting it higher than the timeout (e.g., 10, 15, or 30).

Best regards,

[Erlandas]

I have performed the requested tests and attached screenshots for reference.

I connected the device directly and used ModRSsim for Modbus serial communication testing. Despite the correct configuration, the result remains the same – communication error is displayed during the test.

Additionally, I have also tried adjusting the Period value to 60 and increasing it beyond the timeout (10, 15, and 30), but unfortunately, this did not resolve the issue.

Please let me know if there are any further troubleshooting steps you would recommend.

Best regards,

[Martynas]

Thank you for performing the tests and providing the screenshots.

To ensure proper RS485 communication, please make sure that D- is shortened with R-, and D+ is shortened with R+, as shown in the picture below:

Let us know if this helps or if you need further assistance.

Best regards,

[Erlandas]

Thank you for your recommendation! Shorting the RS485 connections resolved the communication issue, and I am now receiving data.

However, the received values are all 0,000000, despite the fact that the meter is actively measuring. The same 0,00000 values are also displayed on AWS, but I believe this is likely related to configuration or data representation settings, which I will investigate further.