Cliff

Hi sorry for the delay.
I am running the the inject every 30s but in my testing is can go much faster, actually just put a message limiter inline as the messages all fire out of the timestamp in parallel, at 4 msg/s I have never had any corruption issues.  
Inverter settings are below. 
If you still having issues it could be the rs885 converter remember 485 is async so the adaptor needs to transmit and then shift to listening mode. 
 

I have a Deye, OEM Sunsynk. All the Sunsynk guides I followed worked 100% without needing to convert. The Modpus protocol sheet also 100% compatible.
The only difference I know of is the physical enclosure and the menus / icons on the little lcd touchscreen...
Innes

This has been a great thread and big learning curve. Big thanks for all the input from everyone, I have also been able to extract the data via rs485 and build first draft dashboard for my Sunsynk 5.5kw. (The data will still smooth out 😀)
Doing this via below path with 1 min update:
1) Synsync-> Rs485 -> RPi4 -> Node Red(on RPi) -> InfluxDB (On Rpi) -> Grafana(on Rpi)
2) AGM Battery -> BMV -> RPi4 -> Node Red -> InfluxDB -> Grafana

 
I have also tried to map the Modbus registers to the  values on the Sunsync display that could assist. (might be room for improvement or corrections)