I did this overview to show all the property electrical systems and wanted to include the Offgrid solar/battery I have for the workshop Garage.
I’ve no mains supply to the workshop/garage and it’s outside the range of the home wifi. I still wanted to have an idea of what the state of the battery is and get some alarms if the voltage dips too low.
The charge controller for the battery has an RS485 port which provides some access to some data via Modus. I’ve built a node that makes Modbus calls to the Charge controller over the RS885 from a few registers and then passes it back to the EmonPI via 868mhz the same way as the other EmonPI nodes do it, like an emonTH.
So the code has sections similar to an emonTH V2 and the remainder of the code is for the Modbus calls. It was a hassle getting the Modbus to work. I was used to throwing Modbus calls to PLCs at work for hundreds of registers with quick update times. I really had to place long delays between the calls to each register in the charge controller, but then it works and I get voltages and currents from the charge controller and feed these back to the EmonPI roughly every 20 Seconds. I also have counters for Modbus Exceptions and comms failures that I pass back to the EmonPI.
Hardware .
Arduino Pro Mini mounted on a bit of Veroboard.
Jeelabs Shop : RFM69CW Radio kit.
Waveshare rs232/rs485 converter (2wire)
It’s a bit of a lashup in that case and you always intend to come back to it and tidy it up. But it works right and it’s been reliable ever since. It draws a 7.5v supply from the charge controller for the Arduino.