Modbus intermittent failures

LargeBlackcurrant · Wed Nov 12, 2025 11:34 pm

Hi all,

I have a Fox KH10 and since it was installed have had an Elfin EP11 connected to it and have been reading data from the inverter with no issues at all since then. The inverter was restarted two days ago due to a fault and since then I've been getting the following errors in Home Assistant:

Code: Select all

Error connecting to inverter (friendly name: ""). Error reading registers. Type: RegisterType.HOLDING; start: 31000; count: 43; slave: 247 from tcp://192.168.30.130:502: Modbus Error: [Input/Output] Modbus Error: [Connection] CustomModbusTcpClient 192.168.30.130:502: Connection unexpectedly closed 0.001 seconds into read of unbounded read bytes without response from slave before it closed connection

The strange thing is that if I wait a bit (maybe 10 minutes or so) it will successfully get a reading from the inverter, but then after trying again for about a minute will error out in the same way.

Things I have tried to remedy this:

Restarting the inverter again

Restarting the Elfin EW11

Confirmed all serial settings on the EW11 are correct

Confirmed slave ID in the inverter is correct (247)

Removing and recreating the device in Home Assistant

Updating the HA integration from the latest (1.13.6) to the latest pre-release (1.14.0b3)

Modifying the Max Read and Poll Rate in Home Assistant to lower/higher values

Still, I have the same symptoms. If anyone is able to assist I would be so appreciative!

Thu Nov 13, 2025 8:17 am

The intermittency suggests a comms fault or faulty EW11, i’ve heard from previous users that they are very susceptible to power supply and they’ve fitted a 12V 1A power supply which sorted the problems - also worth checking you have latest firmware.

What length is your RS485 cabling and what cable have you used ? - if it’s running less than a few metres it doesn’t matter what cable you use but any longer than that it should be twisted pair to the A & B and you should not connect any ground connection (they are a differential pair).

These are real time comms, polling every few seconds and so any weakness in the wifi signal or a busy network can be an issue - you might be able to reduce the load by going into Devices & Services, select the Foxess Modbus one and click Configure and choose advanced options - change your Max Read setting to 25 and submit.

LargeBlackcurrant · Thu Nov 13, 2025 8:40 am

Thanks for your response.

For data cabling I'm using one pair in a cat5e cable (the other three pairs are just not terminated to anything). Power supply is currently from the USB port on the inverter using a USB cable that only has + and - power, so it should be 5v 1A. As mentioned it was very stable for about a month.

I've tried reducing the max read all the way down to 10 with no luck unfortunately.

I would like to try introducing a better power supply but not sure how I'd get a 12v supply to the location of the inverter. What solutions have you seen for this?

Thanks again for your assistance