Fault finding

Startup process

The addon follows the following startup process:

1. Load config, sensor definitions and schedules

   The logs will show if you use any unknown or deprecated sensors, if you have anything wrong in your custom sensors, and the intended schedule for reading sensors.

2. Connect to the Inverter

   Connect and read the inverter identity (device type, protocol, serial) from registers 0–7, then rated power from the selected sensor definitions. This is the first step to ensure the connection is working.

   If this read fails, you need to follow the fault finding guide below. It could be a cabling issue, a configuration issue, or a hardware issue.

   If successful, the serial number in your config is checked against the inverter. A warning is logged when SENSOR_DEFINITIONS does not match the device type. The log will show identity details and the rated-power startup read.

   If the identity and rated power reads succeed, it will read all configured sensors to ensure you have some values at startup

3. Connect to the MQTT server

   Publish the discovery data for Home Assistant, and also remove discovery data if required

   If this step fails, you will not see any entities in Home Assistant and you need to check your MQTT server settings.

Once the startup is complete, the addon will continue to read & publish sensor data. During this process you will occasionally see read failures. As long as this does not happen on every read, you can probably continue using the addon, but can consider reducing sensors, relaxing the read schedules, etc.

If you poll several inverters on one RS485 bus and one unit stops replying, it might enter a stale state so the bus is not blocked. Tune STALE_INVERTER_AFTER_SECONDS and STALE_INVERTER_SKIP_SECONDS in the Supervisor options (see Multi add-on options). After each successful Modbus read, a timer is armed: if reads are still failing once that many seconds have passed since the last success, the add-on pauses normal polling for that inverter for the configured skip period, then probes the serial register once before resuming or extending stale quiet.

A parallel AC setup (inverter Parallel Mode Client / Server) does not mean both inverters share the RS485 Modbus bus. If the second inverter never appears, see Parallel inverters below.

If you fail to get a reply from the inverter, typically if step #2 fails, please check the following:

(A) Cabling & connection

While fault finding use as short as possible cable, outside any sprague/trunking. Once everything works, you can switch to a more permanent, much longer cable.

If you cannot establish a connection, check the RS485 adaptor and cabling. Are you plugged into the correct port, is your connector crimped correctly?

TIP

Many newer Sunsynk/Deye hybrids use one BMS RJ45 socket for both RS485 (what this add-on uses) and CAN (battery management). If the battery already uses that port, you cannot simply “share” a normal patch cable—you need a splitter or Y-cable that keeps CAN on its pair and RS485 on pins 1–3 only on the adaptor leg. Pinout, splitter layouts, and what goes wrong if all eight wires are duplicated to both sides are covered in Adaptors & Wiring (continue through If the battery already uses this port and Pin reference).

Other factors that might impact connection, or reliability:

• Use a RJ45 converter with a GROUND pin. Ensure the ground is connected.
• Re-crimp your RJ45 connector.
• Use a good quality solid CAT5e/CAT6 cable.
  • Ensure the data line is using a twisted pair.
• Ensure your RS485 cable does not run parallel to other electrical cables (AC or DC), to reduce interference. e.g. in trunking.
  • If interference is a problem, are you using a twisted pair in the cable?
  • If interference is a problem, it could also help to use a shielded cable. Ground the shield at ONE end only (i.e. on the USB adaptor side and then just use normal plastic RJ45 connector on the inverter side.)
• If you still fail to make a connection, test the line voltage resistor (see Reducing timeouts below)

(B) Configuration

Check the Modbus Server ID

Ensure the Modbus Server ID (MODBUS_ID config setting) matches the configured Modbus SN value of the inverter. This value must not be zero.

View/update the Modbus server ID on your inverter under "Advanced Settings" / "Multi-Inverter".

Please note that this can be reset to zero after a software upgrade on your inverter, and this will stop the addon from reading data from your inverter. Resetting it to the previous value (the value the value in MODBUS_ID if you had this working previously), and then restarting the inverter should fix the issue.

Only a single connection to the serial port

Ensure you only have a single addon connected to the serial port. The following can all potentially access the USB port: mbusd, Node RED, the normal and dev addon version.

If you need to have multiple connections to the serial port: ONLY connect mbusd to the serial port. Connect all addons to mbusd (e.g. tcp://192.168.1.x:503).

(C) Reducing timeouts

If you get many timeouts, or if the addon does not read all your sensors on startup (i.e. you see Retrying individual sensors in the log), you can try the following. The RS485 timeout diagnostic sensor on each inverter (Stats) shows whether timeouts are still climbing.

• Set READ_SENSORS_BATCH_SIZE to a smaller value, i.e. 8.
• Direct serial and TCP wait READ_MESSAGE_SPACING seconds after each reply (default 0.05). Raising TIMEOUT only waits longer for a missing reply; it does not add that gap. Try 0.1 or 0.15 if timeouts continue.
• The most reliable way to connect is to use mbusd to the serial port & connect the addon to mbusd at tcp://<ip>:502. The mbusd instance/addon can be on the same physical device or a remote device. mbusd, pymodbus, and the add-on each have their own wait — see Wait times by component.

Check the cabling and connection again. Use a 1m cable and stand next to the inverter while testing.

Direct serial

If your RS485 adaptor is plugged directly into your host, connecting directly to the serial port PORT: "/usb/ttyX" might not give you the best results.

Once you have a working connection (reading the serial), consider introducing mbusd into your setup, in this configuration mbus connects to the serial port and the addon connects via TCP, typically: PORT: tcp://homeassistant.local:502

mbusd over tcp:// is a reliable setup. Direct serial (PORT: /dev/ttyUSB0) is also supported (tmodbus); see configuration. If direct serial is flaky, prefer mbusd.

Check line voltage / termination resistor

If your RS485 adapter has a termination resistor (typically 120 ohms), try removing it.

To check, disconnect the adapter and use a multimeter to measure the resistance between A & B.

The d.c. voltage between A/B on the sunsynk RS485 connection should idle around 4-5v with nothing connected, but this may drop to around 0.5v with the 120 ohm load.

RS485 devices are typically multi-drop with a termination resistor on the first and last devices. However, the RS485 BMS port may only be intended to connect to a single device.

(D) Parallel inverters — second inverter not responding

The add-on can poll several inverters on one adaptor when they share a physical RS485 bus: same PORT, unique MODBUS_ID (and SERIAL_NR / HA_PREFIX) per unit. See Shared RS485 bus.

Parallel Mode does not automatically daisy-chain Modbus. If only one inverter answers, or the other goes stale / startup shows no response, test one inverter at a time with the same USB adaptor. Change only which RJ45 you plug into and the single INVERTERS entry. The inverter LCD may still say Master / Slave for Parallel Mode; this add-on uses Client / Server. See Modbus.

1. Baseline — inverter 1 only. Plug the cable into inverter 1. Configure one INVERTERS entry for that unit (MODBUS_ID matching its Modbus SN). If this fails, it is a normal connection problem — follow (A)–(C).

2. Inverter 2 on its own socket. Move the same cable to inverter 2. Change the config to inverter 2 only (HA_PREFIX, MODBUS_ID, SERIAL_NR). If this fails while plugged into inverter 2, inverter 2 is not answering Modbus: check its Modbus SN, cabling, and whether that model exposes RS485 on the port you are using when Parallel Mode is Server.

3. Is the bus shared? Plug the cable back into inverter 1. Keep the inverter 1 config. Then move the cable to inverter 2 without changing the config.

   • If inverter 1 still answers with the cable on inverter 2, the RS485 bus is shared — use the same PORT for both INVERTERS entries, with unique MODBUS_IDs.
   • If it goes silent, the bus is not shared. Use two adaptors (two PORTs), one per inverter.

4. Optional cross-check. Cable on inverter 1, config for inverter 2 only. A reply means inverter 2 is reachable through inverter 1's socket (shared bus). No reply means the bus is not shared, or inverter 2's MODBUS_ID is wrong.

When using two adaptors, MODBUS_ID must match whatever unit actually answers on that adaptor. Some units in Server mode still answer as 1 on their own RS485 port even when the display shows a different Modbus SN.

Stats

Each inverter publishes two diagnostic MQTT entities (not listed under SENSORS). They appear on the inverter device in Home Assistant under Diagnostic, and update every 120 seconds.

RS485 timeout

Cumulative Modbus timeout count for that inverter since the add-on started (reads and writes, including gateway 0x0B). Occasional increases are normal. A steadily rising count means the bus is dropping replies — see (C) Reducing timeouts.

Callback stats

Duration of that inverter's poll cycle. The state is the mean time in seconds over the last 120s. Attributes add count, min, max, median, stdev, p5, p95, plus:

• busy_count — a new poll was skipped because the previous one was still running
• error_count — the poll raised an error

If mean / p95 approach the schedule interval, or busy_count climbs, the add-on cannot keep up: reduce sensors, relax schedules, or fix timeouts. error_count should stay near zero.