Local Modbus access for Solis inverters, with Solis Cloud still working

Solis hybrid inverters have a single 4-pin COM port, and that’s where the Solis datalogger dongle plugs in. The dongle acts as a Modbus RTU master: it regularly polls the inverter over RS485 and uploads the readings to Solis Cloud. That works well, but it leaves no obvious way to read the same data locally for Home Assistant, battery automation or your own logging.

The difficulty is that Modbus RTU only allows one master on an RS485 bus. If you connect a second adapter to the same pair, sooner or later both will transmit at the same time. The messages collide, replies are corrupted or go to the wrong device, and both ends start seeing timeouts.

The common workarounds all have a downside. Unplugging the dongle gives you clean local access, but you lose Solis Cloud, the app and your installer’s remote access. Some dataloggers can provide Modbus TCP themselves, but not reliably: the S2-WL-ST only accepts one TCP connection and can drop off the cloud while an integration is connected, and the DLS-W and S3-WIFI-ST don’t offer Modbus TCP at all.¹

This guide takes the gateway approach. It’s based on alienatedsec’s solis-ha-modbus-cloud design, which uses two single-channel Waveshare RS485-to-Ethernet converters.¹ Here, the same idea is built on a single Waveshare 4-CH RS485 TO POE ETH (B), which has four independent, isolated RS485 channels, each with its own IP address, behind one PoE network port.² That leaves one channel free for a Pylontech battery stack, and another spare.

A small splitter divides the COM connection in two, so the inverter and the dongle each have their own RS485 pair, connected to separate channels on the Waveshare gateway. Each channel has its own job:

• RS485-1 (192.168.1.201) is wired to the inverter and acts as a Modbus TCP server on port 502. In multi-host mode it accepts connections from several TCP clients and passes their requests to the inverter one at a time.
• RS485-2 (192.168.1.202) is wired to the dongle. It converts the dongle’s RTU requests into Modbus TCP, forwards them to RS485-1 and passes the replies back.
• RS485-3 (192.168.1.203) is an optional, transparent link to the Pylontech battery’s RS485 port. The battery doesn’t use Modbus, so the gateway simply passes the data through unchanged.

As far as the dongle is concerned, it’s still talking directly to the inverter, so Solis Cloud, the app and remote control all carry on working. Home Assistant connects to 192.168.1.201 on port 502, just like any other Modbus TCP device.

How requests are kept apart

In multi-host mode, the gateway only ever has one request outstanding on the RS485 bus. If a second request arrives, from either the dongle or Home Assistant, it’s held until the first reply comes back. Two settings control the timing: the gateway waits up to 256 ms for a reply before giving up, and only transmits once the bus has been idle for 20 ms. Both values come from alienatedsec’s configuration.

There’s also a useful side effect. Because the two halves are only linked over TCP, they don’t need to run at the same speed. The dongle side has to match the dongle (9600 baud), but the inverter side can be increased later if your inverter supports a faster Modbus speed.

The gateway modes, timings and splitter idea all come from alienatedsec’s solis-ha-modbus-cloud project. This guide adapts them for the 4-channel unit and adds pinouts, channel assignments and test scripts.

Compatible dataloggers

alienatedsec lists the DLS-W, DLS-L, S2-WL-ST and S3-WIFI-ST as working with this setup, with the 4-pin S1-W4G-ST untested. Dataloggers with a USB connector, as used on the S6 range, won’t fit a 4-pin splitter.¹

The dongle-side channel has to match the dongle’s serial speed. The S2-WL-ST and S3-WIFI-ST default to 9600 baud, and on a DLS-W the speed can be changed from a hidden page at /config_hide.html.

Solis COM port

The COM port is the green 4-pin Exceedconn connector on the underside of the inverter. Solis’s own troubleshooting article lists the pin functions and includes photos of the connector.³

Waveshare 4-CH terminals

The gateway has a 6-way terminal block at the Ethernet end for channels 1 and 2, and an 8-way block at the other end for the power input and channels 3 and 4. Each channel has its own A+, B− and signal ground terminals. Using channels 1 and 2 for the splitter keeps both pairs at the same end of the unit.²

These addresses are examples for a 192.168.1.x network. Any free static addresses will do, but matching each address to its channel number makes the rest of the setup easier to follow. The Pylontech RJ45 pin definitions are in section 09, alongside the battery wiring.

It’s easiest to do this on the bench before going anywhere near the inverter, so the installation itself is just a case of plugging things in. Use VirCom for the configuration rather than the built-in web page, as alienatedsec recommends. The multi-host options are in its More Advanced Settings dialog.

RS485-1 settings (inverter gateway)

Double-click RS485-1, enter the settings below, then click More Advanced Settings… for the multi-host options. When you’re done, click Modify Setting, then Restart Dev.

RS485-2 settings (dongle bridge)

RS485-3 and RS485-4 settings

RS485-4 can be left on its factory settings.

Checking the configuration

From a PC on the same network, run the following in PowerShell. It should report TcpTestSucceeded : True.

Test-NetConnection 192.168.1.201 -Port 502

If you run the read test at this stage, it should connect and then time out, as nothing is wired up yet.

If you lose track of a channel’s address, holding the reset button for 5 seconds restores the factory settings, including the default address of 192.168.1.254. If the web page stops loading after trying Waveshare’s MQTT or JSON firmware, the web files can be reloaded from the wiki; VirCom continues to work either way.²

The splitter is the only part you need to wire yourself. A female plug fits the inverter’s COM port, and its 5 V supply is passed straight through to a panel-mounted male socket for the dongle. The two RS485 pairs are not linked through; each one goes to its own Waveshare channel.

Before connecting anything to the inverter, check the following with a meter, with everything unpowered:

• There is continuity between plug pin 1 and socket pin 1, and between plug pin 2 and socket pin 2.
• There is no continuity between plug pins 3/4 and socket pins 3/4. If they’re connected, you’ve put two masters back on the same bus.
• There are no shorts between any two pins on the plug, and pin 1 connects to nothing other than socket pin 1.
• Plug pin 3 connects to RS485-1 A+, and socket pin 3 connects to RS485-2 A+.

Termination resistors aren’t needed. alienatedsec notes that both the inverter and the Waveshare already terminate the bus, so don’t add 120 Ω resistors. Connecting only A and B normally works because the Waveshare channels are isolated, but if you see errors on a longer cable run, connect each channel’s signal ground to pin 2 (0 V) on the same side.¹

Work through the three checks below in order. If one fails, it points to a specific half of the system, which keeps fault-finding quick.

Reading the inverter directly

solis_read_test.py reads a handful of input registers through the gateway, using only Python’s standard library. It doesn’t write anything to the inverter. Run it from any PC on the network and compare the results with the inverter’s display. The output should look something like this, although your figures will be different:

> python solis_read_test.py 192.168.1.201 502 1
Connected to 192.168.1.201:502, unit 1
Inverter clock   : 2026-10-06 13:45:30
PV power         : 2350 W
Inverter AC power: 1195 W
Inverter temp    : 41.2 C
Battery voltage  : 52.3 V
Battery current  : 22.0 A (charging)
Battery SOC      : 77 %
House load       : 640 W
Battery power    : 1150 W

Running it for a day

Leave it polling every 5 to 15 seconds for a day, and check that Solis Cloud keeps updating throughout. alienatedsec found the setup more reliable with frequent polling, around every 5 seconds, than with long gaps between reads.¹

If the read test times out but Solis Cloud is working, try swapping A and B on RS485-1. If Solis Cloud has stopped updating but the read test works, the problem is on the RS485-2 side. Swapping A and B on an RS485 connection won’t cause any damage.

The 4-CH unit only has RS485 channels, so it can’t use the Console port that most Pylontech monitoring projects connect to, because that port is RS232. Use the B/RS485 port on the master battery instead. It uses Pylontech’s own ASCII protocol rather than Modbus, so RS485-3 is set to pass data straight through, and the protocol is handled by software on your network.

python pylontech_test.py 192.168.1.203 4196 2 9

For ongoing monitoring, python-pylontech can connect to the channel through a socat virtual serial port on Linux. On Windows, VirCom can map RS485-3 to a virtual COM port for Pylontech’s own PC software, which is how alienatedsec monitors their batteries.^1,7 If the RS485 port won’t work alongside CAN, the alternative is to use the Console port with an RS232 interface, such as a Waveshare RS232/485/422 TO POE ETH, or an ESP32 with a MAX3232 as used by the ESPHome Pylontech component.⁹

• Always connect to 192.168.1.201:502. The 192.168.1.202 channel is reserved for the dongle.
• Only run one local Modbus integration at a time, as two would double the traffic on the bus.
• Set the polling interval to between 5 and 15 seconds.
• Both Solis Cloud and your automations can change settings such as charge times. Decide which one is in charge of each setting, so they don’t keep overriding each other.
• Holding registers (43xxx) contain settings. Reading them is fine, but only write to them when you mean to, and never in a tight loop.

Solis input registers used by the test script

Modbus function 04, unit 1. Register addresses are as used by the homeassistant-solax-modbus Solis plugin, and 32-bit values are sent high word first.¹⁰

Related projects

• alienatedsec / solis-ha-modbus-cloud: the two-Waveshare design this guide is based on.
• homeassistant-solax-modbus, and its notes on setting up Modbus adapters.
• solis_modbus: a Home Assistant integration specifically for Solis inverters.
• Predbat: battery charge planning that runs on top of a local integration.
• python-pylontech: a Python implementation of the Pylontech RS485 protocol.
• ESPHome Pylontech: monitoring through the Console port using an ESP32.