RPi4 - Modbus performance question

Hey Guys,

I am about to get some new solar inverters and one of things that they want is to have their own 3 phase energy meters (each of them so i will end up with 3 x 3 phase meters)

Someone has hacked the modbus protocol between the inverters and the energy meter and worked out that the inverters ask for 8 registers from the energy monitor every 200ms.

Would NR sitting on a PI that was dedicated to this task be able to keep up with this speed of data. ? or would i be better off dedicating an older laptop to the role ?

The Setup would be 1 x RS485 Modbus RTU at 9600 inbound from the energy meter and 3 x RS485 Modbus RTU at 9600 outbound (same information sent 3 times)



Just wanted to revive this one to see if anyone has any thoughts on this?

My idea would be to get a USB 3 hub and hang 3 of the USB to RS485 connectors off it

On the other end i need to emulate the same thing where i have the output from this first RPI go to a 2nd unit that will then talk to the 3 inverters that control the batteries - this is not quite as time critical as the responses can be given at a little further apart.


There really isn't any simple way to be certain without testing it. However I would expect that fetching the data is unlikely to be the critical path, more likely it will depend on what you want to do with the data once you have fetched it.

thanks Colin,

All i will be doing is pushing it out onto the network (cabled to a gigabit switch) - i will either broadcast it as UDP which seems to be the "lightest" way to get it and then listen to the UDP at the other end on another PI

Essentially i have to take the total power draw for the house (from the 3 phases) - add it together - send it out - catch it at the other end, and divide it by 3 so each battery services 1/3 of the load.


In that case don't worry about the loading. I suggest using MQTT. That will be a trivial load. Mosquitto on a pi4 will handle many hundreds, if not thousands, of MQTT messages a second. Probably a Pi zero would handle your requirement.

OK sounds good - will start with a Pi4 and scale back if it does look like it is idling - can always redeploy a PI !!

thanks Colin


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