Issue reading modbus registers from Epever uPower charger / inverter using pymodbus

Question

I am having a issue reading modbus registers from a Epever uPower solar charger / inverter. I am using the pymodbus library running on a Raspberry Pi talking over a USB to RS485 cable. I know the hardware and the cable are working because I can get the data on a Windows laptop. It also appears to work on the PI as when I select a different unit ID in the code below I get a connection error.

There are many well documented examples of reading registers from Epever equipment and the following code seems to work with most devices however I can not get it working with the newer uPower device:

import logging
logging.basicConfig()
log = logging.getLogger()
log.setLevel(logging.DEBUG)

client = ModbusClient(method = 'rtu', port = '/dev/ttyUSB0', baudrate = 115200, stopbits=1, timeout=1, parity='N' )
client.connect()
 
result = client.read_input_registers(0x3100,6,unit=10)
print(result.registers)
solarVoltage = float(result.registers[0] / 100.0)
solarCurrent = float(result.registers[1] / 100.0)
batteryVoltage = float(result.registers[4] / 100.0)
chargeCurrent = float(result.registers[5] / 100.0)
 
# Do something with the data
 
client.close()

The debug logs show the following:

DEBUG:pymodbus.transaction:Running transaction 1
DEBUG:pymodbus.transaction:SEND: 0xa 0x4 0x31 0x0 0x0 0x6 0x7f 0x8f
DEBUG:pymodbus.client.sync:New Transaction state 'SENDING'
DEBUG:pymodbus.transaction:Changing transaction state from 'SENDING' to 'WAITING FOR REPLY'
DEBUG:pymodbus.transaction:Changing transaction state from 'WAITING FOR REPLY' to 'PROCESSING REPLY'
DEBUG:pymodbus.transaction:RECV: 0xa 0x84 0x2 0xb3 0x3
DEBUG:pymodbus.framer.rtu_framer:Getting Frame - 0x84 0x2
DEBUG:pymodbus.factory:Factory Response[132]
DEBUG:pymodbus.framer.rtu_framer:Frame advanced, resetting header!!
DEBUG:pymodbus.transaction:Adding transaction 10
DEBUG:pymodbus.transaction:Getting transaction 10
DEBUG:pymodbus.transaction:Changing transaction state from 'PROCESSING REPLY' to 'TRANSACTION_COMPLETE'
Traceback (most recent call last):
  File "main.py", line 11, in <module>
    print(result.registers)
AttributeError: 'ExceptionResponse' object has no attribute 'registers'

Any help or pointers gratefully received. Would maybe help if I could understand the response that the code is getting RECV: 0xa 0x84 0x2 0xb3 0x3

Either way it does not seem to have any registers....

Answer 1

You need to change your Address from 0x3100 to 0x3500.

I decompiled the SolarStationSoftware and found out that they changed the Realtime Address to 13568.

Answer 2

From looking at the Modbus specification, it appears the exception function code listed in your response (0x0A) is GATEWAY PATH UNAVAILABLE. This means the problem is likely with your RS485 bus. You may get more information from adding an isError() check:

result = client.read_input_registers(0x3100,6,unit=10)
assert(not result.isError())
print(result.registers)