This dashboard project is for the following purposes:
1. Improving performance of the heaters on the batteries.
2. Reducing RFI from the solar panels.
3. Displaying status such as the Flexradio final transistors temperature.
Hardware is a Raspberry Pi 4 located at the remote site, connected over the LAN to Web relays.
Modbus
The flow first polls Modbus data from the solar controllers and in turn performs actions like closing relays. A Node Red flow polls the modbus, then converts the modbus floating point data to readable decimal, and finally, turns relays on and off. One feature improves the battery heater operation by bypassing the thermostats as needed. Another feature reduces RFI by disconnecting the solar panels from the solar controllers when batteries are fully charged. The most difficult task so far has been converting the floating point data to decimal. That flow is what is discussed first.
Data from the modbus is in the format of IEEE 754 half precision 16 bit floating point Little Endian which is unreadable by humans. Many JavaScript functions are available to perform a conversion operation but they have all proved impossible to implement during this project. Thanks to chatGPT a solution was finally implemented that works. It took 7 iterations of chatGPT to develop a Node Red function node which produced the correct output and no errors. The successful node is shown below to get it down on paper for preservation.
It was a huge milestone to get the floating point conversion node working. Below is what the output of the big achievement looks like. The number is the actual voltage of the 24 volt battery as measured by the solar controller and processed by the Node Red flow.
It’s easy to confuse the use of the word “function”. To offer some clarity, the node above is a Node Red “function” node. Inside this function node is a JavaScript “function”. The JavaScript function is the first thing in the node. The JavaScript function is declared and defined, making it ready to be used. Next element is at the bottom and that is where the JavaScript function is called, data is passed to it, and the output is moved into the msg.payload object.
The Flow
The object is passed to the next Node Red node which is a debug node (debug 22).
On the left above is the Modbus Read node, named Stras 88. It’s settings are shown below.
In the Server field above, the name is Stras 88 which indicates the location of the solar controller and the port number. It’s I.P. address is entered by clicking on the pencil icon on the right. The Address in the Address field is obtained from the Morningstar documentation. The FC field is always FC 3 when reading a holding register per the Modbus specifications.
A big project has begun. Onward to the next part, the outputs.
OUTPUTS
Microbit RemoteRig 1216H Webswitch relays will be used because they are already in place from an earlier project. See https://w0qlremotebase.wordpress.com/2021/05/01/noise-chase/.
These relays are currently wired up to remotely turn on and off the solar panels from the solar controllers manually. Despite mechanically working perfectly, turning on and off the relays manually did not happen. Too much work? Along came Node Red and this function can now be down automatically. First, the command set for the 1216H is available on the Webswitch website and also posted elsewhere in this journal: https://w0qlremotebase.wordpress.com/2023/02/12/microbit-remoterig-1216h-webswitch-command-set/
TESTING
In Node Red a node called EXEC can be used to execute a command. The command can use curl to send a web request over the internet to the 1216H, and the response will be the status of that request. In the flow below, an http request is encapsulated in a curl command in an exec node:
The configuration in the exec node is shown below, with a fake I.P. address. Enter your own here.
In the next chapter some nodes will be wired together in such a way as to turn off the solar panels when the battery is fully charged and RFI is occurring.
Step 1 is to do a modbus read of a solar controller looking for the High Voltage Disconnect (HVD) bit. Morningstar controllers have this feature when using Lithium batteries. When the HVD bit is positive, tell the 1216H to close a relay corresponding to that controller. The closure in turn opens a higher current relay and disconnects the panels. Boom. RFI stops.
W0QL - My Remote Base Journal 