Solar-power-battery-monitoring

Tessel project to monitor battery load status using Hall-effect sensor.

We have samll off-the-grid solar power system at our summer cottage which
provides electricity for LED-lights and devices. I have explored ways
to monitor this system as a hobby.

This repository might in future contain software for this monitoring system.
Readme contains description of the solar power and monitoring systems and
work log my progress of monitoring project.

Hardware

Solar power system

• 200W of PV panels
• Morningstar SunSaver MPPT 15A Charge controller
• Victron 220Ah battery
• 600W inverter

Monitoring electronics

• Tessel
  • Climate module if I want to monitor temperature or humidity
  • GPRS module which can be used to send data to server
• Panucatt Devices 50A hall-effect Bi-directional current sensor
  • Non-invasive version would be easier to install, but this accepts wider supply voltage
• Texas Instruments ADS1115 Analog to Digital converter, 16bit preciesion
  • Precision of integrated ADC on Tessel is only 10bit and I think more is required for precise measurement
  • Pre-soldered board available from Adafruit
  • I ported a library for Tessel from Adafruit’s Python code

Software

• Tessel program, tessel/
• Server software
  • Store measurement data
  • Display graphs

Work log

23-25.7.

• I managed to solder ADC ics to MSOP adapter boards, 2 of 3 chips survived
• Ported basic functionality of Adafruits ADS1115 library to Node
• Connected ADC to Tessel using solderless breadboard
  • Added pull-up resistors to SCL and SCLK lines
  • 100nF capacitor on Vdd
  • AIN0 connected to Hall-sensor Vout
  • AIN1 connected to 0.5 Vdd, to provide comparison for Hall-sensor (resistive voltage divider, R1,R2 = 12kOhm)
• Tested current sensor by measuring current of 3W led
• Problem: ADC seems accurate but Hall-sensor output doesn’t seem to be exactly 0.5 Vdd when there is no load
  • Read that e.g. earths magnetic field might affect sensor
  • Some kind of calibration is required. Automatic calibration should be possible if I can identify when there is no load…