Issue with Modbus RS485 Communication on Deye SUN-33K-G Inverter (GRID TIED)

[GabrielSk82020]

Hi everyone,

I'm currently testing Modbus RS485 communication with inverters from Deye, and I’ve run into an issue with the SUN-33K-G model.

So far, I’ve successfully tested the SUN-12K-G using an RS485 to TTL adapter (with TX/RX LEDs). I'm connecting via the green terminal block on the bottom of the inverter, using pins 3 and 4. Communication works flawlessly — when I send a Modbus read request, the TX LED flashes, followed by the RX LED, just as expected.

However, when I connect the same setup to a SUN-33K-G inverter, things behave differently. The RX LED blinks continuously, approximately every second, regardless of whether I send a request. It seems like the inverter might be acting as a Modbus master instead of a slave — which is unexpected.

Has anyone worked with the SUN-33K-G over RS485?

Is there a setting I need to change to make it behave like a standard Modbus slave?

Is there any documentation specific to Modbus mode or communication roles on this model?

Any insight would be greatly appreciated!

Thanks in advance.

[Waz-Cpt]

Hello There,

I would suggest including pictures of the inverter's connections.

Typically there is an RJ45 port that is used for connection over RS485 (Modbus RTU).

There is extensive information on this matter on both the documentation https://kellerza.github.io/sunsynk/ for this project and on Solar-Assistant website https://solar-assistant.io/help/deye/configuration.

[GabrielSk82020]

Could not find the model in the website you provided, the model we have is a SUN-33K-G. It has a green conector RS485 with 4 pins, I think 1 and 2 are power 5V - pins 3 and 4 are RS 485. Here's q picture of the connector opened.

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On Fri, Jun 27, 2025, 5:44 AM Warwick Davison ***@***.***> wrote: Hello There, I would suggest including pictures of the inverter's connections. Typically there is an RJ45 port that is used for connection over RS485 (Modbus RTU). There is extensive information on this matter on both the documentation https://kellerza.github.io/sunsynk/ <http://url> for this project and on Solar-Assistant website https://solar-assistant.io/help/deye/configuration <http://url>. — Reply to this email directly, view it on GitHub <#489 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AOVCXLFCMEC5P6ONPGAX7D33FT767AVCNFSM6AAAAACAGGZ2MOVHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTGNJZGUZDIMI> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[Waz-Cpt]

It really would help if you provided the exact model details and pictures of your inverter.

Online, there are manuals for the G03 and G04 version of the Grid Tied PV String Inverters.

Neither of them make use of green screw terminals for RS485 comms. They do reference a 4 pin keyed round screw on connector plug for RS485 comms to the external power meter & CT clamps.

There is no signs that data can be gathered on this RS485 port, it is there purely for parallel communication of the inverters and a single power meter.

If you want to gather data, it is likely best to either attempt to use the Solarman based dongle and the solarman driver or connect a USB to RS232 adaptor directly to the data logger port.

This project has not really been designed around the Solar Grid Tied PV String inverters.

From the image from the manual it is clear that the primary inverter only operates as a Modbus master unit when connected for the power meter.

[GabrielSk82020]

Hello! I finally got it working with help from the Deye Sun customer support team. Here's what fixed it:

They tested a few firmware updates on the inverter, specifically the Communication CPU Software Version. The version that worked for me was V0.2.4.8.

One thing to note: this update alone doesn't automatically enable the green RS485 COM port in SLAVE mode. By default, the inverter may still act as MASTER.

To switch it to SLAVE mode:

Go to the COM Settings (where you set the SLAVE ID and BAUDRATE).

After the update, a new option appears just below those fields — here you can select either METER or 485.

Choose 485 to force the inverter into SLAVE mode.

In case this option doesn't appear under COM Settings on your model, here's the alternative path where it may be found:

Setup → Run Param → Meter On (hold Enter for 3 seconds to reveal a hidden menu)

Then go to: Shunt → Slave

After making this change, the inverter finally stopped acting as MASTER, and I was able to connect and use my custom hardware with it successfully.

For reference, here in Brazil the model used is a GRID-TIED inverter SUN-33K-G (the name may vary in other countries).