Source for ready-to-use modbus cable to connect 15k inverter RS485 to USR-TCP232-410S terminal block module

[tobiaskreidl]

I'm looking for a good, quick source for a for ready-to-use modbus cable to connect a Solark15k-2P-N inverter RS485 to the USR-TCP232-410S terminal block that just takes the two power wires and a ground. I can only seem to find ones with a USB end. Would this DMX cable work or please let me know what you've been able to get that works: https://www.ecolocityled.com/product/rj45-to-bare-wire
I don't have access to any crimping tools, so something plug-and-play is highly desirable. Many thanks in advance!

[tobiaskreidl]

Looks like I'll have to construct my own.

[tobiaskreidl]

OK, got it working. Took a standard passthrough RS485 cable and cut off one end. Pin 7 (brown/white stripe) goes to terminal A on modbus device, pin 8 (brown) to terminal B , and pin 6 (green) to Ground. Restarted HA and it all came alive. There are some drop outs which might be from insufficient shielding or lack of 120 ohm termination or who knows what, but it's mostly sending data and HA is picking it up properly. Attached is the RS485 configuration on the modbus unit.
I did not have to do anything on the Solark end other than plug in the RJ45 cable to the modbus port. The Solark in question is the model 15k-2P-N, so there may be variations for other inverters. Check the Solark manual for details. Purportedly, the Battery CANbus port can also be used, as the battery uses different pins.

[pbix]

Glad you got it working. I would advise you to continue with your testing until you get a 100% reliable connection without dropouts. The integration has trouble recovering from connection loss so that's a tip for you.

[tobiaskreidl]

Thank you, @pbix -- the dropouts could happen for a multitude of reasons, which I will have to explore over time. I'm not the only one experiencing dropouts from a few other postings I've seen elsewhere, and unfortunately, none of the folks involved has come up with a fix in their particular cases. I;m not sure a firmware upgrade on the modbus unit would help, plus it's a pretty involved process.
My RS485 cable is of good quality, about 12 feet long, but it is in a machine room which is obviously an electronically "noisy" environment. In any case, If I find a true fix or even make some good headway, I'll post my findings. I'd be interested in what settings anyone else has used with their modbus interface.
P.S. No dropouts for over 10 hours currently, for no obvious reason. Occasionally, the location experiences power glitches which can affect everything electronic and electrical, so I'm not concerned about losing one data point a couple of times a day due to that.
P.P.S. Have not seen any logged errors since Dec. 29. This update is from around 8 AM on Dec. 31. Occasionally, the display shows "unavailable" but it seems to correct itself presently. Hard to tell from the graphs if there are actual small gaps or it's just their limited resolution. The huge gaps from earlier no longer seem to be showing up, which is encouraging.
Now, more gaps showing up primarily at night. Sigh. More research needed ...

[tobiaskreidl]

I've now wrapped the modbus module in foil to try to cut out EMF noise.
When back to this at some point, I may try a better-shielded cable as the only other option I can think of at present other than maybe tweaking the modbus settings some.

Note added 01/01/2026 at 13:30h local time: Foil shielding seems to produce little to no help. Will probably have to try a different cable at a future date and/or experimenting with modbus settings.

FWIW, the error log most recently just before I wrapped it shows the following, which is frankly not terribly helpful other than confirming there was a timeout:

pymodbus.exceptions.ModbusIOException: Modbus Error: [Input/Output] ERROR: No response received of the last requests (default: retries+3), CLOSING CONNECTION.
2026-01-01 10:59:26.508 ERROR (MainThread) [custom_components.solark_modbus.hub] Unexpected error fetching SolArk data
Traceback (most recent call last):
File "/usr/src/homeassistant/homeassistant/helpers/update_coordinator.py", line 419, in _async_refresh
self.data = await self._async_update_data()
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/config/custom_components/solark_modbus/hub.py", line 301, in _async_update_data
realtime_data = await self.hass.async_add_executor_job(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
self.read_modbus_realtime_data
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
)
^
File "/usr/local/lib/python3.13/concurrent/futures/thread.py", line 59, in run
result = self.fn(*self.args, **self.kwargs)
File "/config/custom_components/solark_modbus/hub.py", line 331, in read_modbus_realtime_data
realtime_data = self._read_holding_registers(unit=self.slaveno, address=60, count=21)
File "/config/custom_components/solark_modbus/hub.py", line 285, in _read_holding_registers
return self._client.read_holding_registers(address, count=count, device_id=unit)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/local/lib/python3.13/site-packages/pymodbus/client/mixin.py", line 113, in read_holding_registers
return self.execute(no_response_expected, pdu_reg.ReadHoldingRegistersRequest(address=address, count=count, dev_id=device_id))
~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/local/lib/python3.13/site-packages/pymodbus/client/base.py", line 202, in execute
return self.transaction.sync_execute(no_response_expected, request)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/local/lib/python3.13/site-packages/pymodbus/transaction/transaction.py", line 147, in sync_execute
raise ModbusIOException(
"ERROR: No response received of the last requests (default: retries+3), CLOSING CONNECTION."
)
pymodbus.exceptions.ModbusIOException: Modbus Error: [Input/Output] ERROR: No response received of the last requests (default: retries+3), CLOSING CONNECTION.

[pbix]

You should not progress to using this integration until you have a reliable connection tested with modpoll as described in my instructions. Let it run for several hours and when you have no timeouts you can proceed to using the integration with HA.

If you cannot get the RS-485 device to function reliably with modpoll you should consult with your converters technical support.

When using the converter I recommended I have no timeout errors when I use the default 10 second update rate with my 10k and it is not common to hear of such errors from other users.

[tobiaskreidl]

@pbix, I was not able to get modpoll to work, even though i can ping the device from my PC. So, not sore why, hence stuck with using HA to test. Nothing is in production, so not an issue at this point if it's not working flawlessly yet. My updates are only every 300 seconds, so it's not an overload issue.
AM still supicious that it's the cable. In any case, I will not to be able to get back to this for several months as will be away from the site for that long and will not have remote access.
All other integrations are running flawlessly, so it's something about the physical connection that seems to be the issue. As to the company, I can try but others have not had much success with feedback from them. That's probably the best recourse at this point though, to your point. Thanks again for the feedback and encouragement to pursue this further.

What cable do you use and where did you obtain it?

C:\modpoll-3.16\win>modpoll -m tcp -a 10 -r 1 -c 1 192.168.1.150
modpoll 3.16 - FieldTalk(tm) Modbus(R) Master Simulator
Copyright (c) 2002-2025 proconX Pty Ltd
Visit https://www.modbusdriver.com for Modbus libraries and tools.

Protocol configuration: MODBUS/TCP, FC3
Slave configuration...: address = 10, start reference = 1, count = 1
Communication.........: 192.168.1.150, port 502, t/o 1.00 s, poll rate 1000 ms
Data type.............: 16-bit register, holding register table

-- Polling slave... (Ctrl-C to stop)
Reply time-out!
-- Polling slave... (Ctrl-C to stop)
Reply time-out!
-- Polling slave... (Ctrl-C to stop)
Reply time-out!
-- Polling slave... (Ctrl-C to stop)
^C

[tobiaskreidl]

Should I be connecting to port 26 instead with modpoll for accessing the usr-tcp232-410s device? And should the mode be set to server or client (slave)?