Monitor Photovoltaic (PV) System with LiFePO4 Batteries

Measure:

1. LiFePo4 cell and block voltage
2. Current and voltage from solar panel strings
3. 230 V output current
4. 230 V fallback current

Send data via WiFi to local "IoT Server" and make data accessible in InfluxDB.

STATUS: WIP, partially tested

LiFePO4 (aka LFP) batteries are known as safe and the voltages may not be dangerous for humans.

BUT ... WARNING: LFP batteries contain a lot of Energy! Shorts can cause enormous sparks, melt metal and cause fire.

Check your circuits twice for shorts (soldering problems)! Be careful touching the circuit with metal tools (e.g. multimeter tips). Put the circuit in a safe enclosure!

Sensor Device

The device measures up to 16 voltages and sends them to the IoT Server.

Hardware is cheap and simple, based on:

• an ESP8266 "D1 Mini" controller with WIFI
• a CD74HC4067 as 16 channel (or 74HC4051 as 8 channel) multiplexer board
• Pololu D36V6F3 Step-Down Voltage Regulator for 3.3 V supply

The sensor is designed to connect via a "8s JST XH " y-splitter cable between the battery and the BMS. Alternatively connect Pin1 to "minus", Pin2 to the plus of 1st cell, Pin3 to the plus of 2nd cell and so on.

Sensor Firmware

To upload the firmware to the "D1 Mini" via the Arduino IDE, you must add http://arduino.esp8266.com/stable/package_esp8266com_index.json as "Additiona Boards Manager URLs" in the "File" > "Settings" menu. Then install the newest version in "Tools" > "Board" > "Board Manager" the "esp8266". For me the "NodeMCU v0.9" board works fine.

Then just

• connect the D1 Mini via USB
• double click the bat-mon-firmware.ino to oben it in the Arduino IDE and
• click the "Upload" button to compile the code and program the module

The sensor will read out the voltages once per minute and send them to the "IoT API Server".

WARNING: If you use the Arduino IDE for NodeMCU, you will overwrite the LUA SDK. If you want back the Lua SDK, use the “flasher” to re-install the firmware. You can download the flasher from their Github page https://github.com/nodemcu/nodemcu-flasher.

Server Set Up

The "server" (a PC is ok) need to run an "IoT API Server", where the sensors post readings data and an InfluxDB to store and analyze the data.

To make things as easy, I recommend to run the server and the DB as Docker containers.

InfluxDB

The Influx DB stores the sensor data as timelines. You can query data and show data as graphs on dashboards using your browser.

Prepare a folders for DB, e.g.

mkdir ~/influxdb2
cd ~/influxdb2
mkdir db
mkdir config
export DB_DIR=$PWD

Start InfluxDB docker server:

docker run -p 8086:8086 -d --restart=always --name influxdb \
  -v $DB_DIR/db:/var/lib/influxdb2 \
  -v $DB_DIR/config:/etc/influxdb2 \
  -e DOCKER_INFLUXDB_INIT_USERNAME=mysuerpadmin \
  -e DOCKER_INFLUXDB_INIT_PASSWORD=mysuerpadminpassord \
  -e DOCKER_INFLUXDB_INIT_ORG=my-org \
  -e DOCKER_INFLUXDB_INIT_BUCKET=pv \
  influxdb:2.1-alpine

Open http://localhost:8086 in your browser and finalize the set up.

Finally create or copy an API token for the API server, via "Data" manu and "API Tokens" tab.

IoT API Server

The "API Server" is a tiny JS app and listens on 8899.

Devices can post JSON data to the endpoint http:/server-ip:8899/<bucket>/<data-type>?key=<api-key>

JSON data is e.g.:

{ src: 'Bat1_7', fld: 'U', val: 0.06 }

Start on Console

Put the InfluxDB API key into the two YAML files in the iot-api-server/config/ dir.

If you modify the API_KEY, don't forget to chage that also in the bat-mon-firmware.ino.

To start the server on the console for testing, execute:

cd iot-api-server
npm install
export NODE_ENV=DEV
node app.js

To send some test data execute: mocha test/testPostApiSvr.js

Run as Docker Server

Build and install the IoT API Server:

cd iot-api-server
docker build -t mh/iot-api-server .
docker rm iot-api-server
docker run -d -e NODE_ENV=MAIN --link influxdb:influxdb  -p 8899:8899  --name iot-api-server  mh/iot-api-server

To send some test data execute (require npm install -g mocha once):

export NODE_ENV=DEV
mocha test/testPostApiSvr.js