Last month I did buy a 2kW photovoltaic system for my house. To connect the pv panels to the grid I bought the Sunny Boy 2100TL inverter from SMA. Unfortunately, it comes without any communication interface in standard configuration. The price for the so called RS485 piggyback interface card is around 90 Euros. On sales pictures it seems to contain only a DC/DC converter and some optocouplers for galvanic isolation and the RS485 driver itself.
I did some research and was able to find out the pinout of the 14 pin and 10 pin header. The 14 pin header is on the “hot” side of the inverter and provides an UART interface with RXD, TXD and RTS signals. For first tests I decided to build a simple galvanic isolated UART adapter using Analog Devices iCouplers. Together with a FTDI USB to TTL adapter I will be able to test everything very fast.
Later I like to use mbed or Arduino to log data on sd-card.
At this point I need to warn you: There is risky high voltage inside of the inverter! Only open it after 15min after it has been disconnected from the pv panels and the grid!
The first PCB was designed for two 2 channel iCouplers of the type ADUM1201. One for the RXD and TXD and one for RTS and CTS signals. Later I found out, that only RXD and TXD is used for communication. Below you can see the PCB of the first version.
Complete assembled PCB and connector for the FTDI TTL-232R-3V3 USB adapter.
I have updated the PCB design and attach the Eagle design:
Eagle project files: SMA piggyback UART schematic and PCB