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Test 1: Battery Life

Objective:

The goal of this test was to determine how long the data logger could operate on a fully charged battery under normal operating conditions, as well as to assess its overall power consumption profile.

Method:

  1. Fully Charged the Battery:

    • Verified that the battery was completely charged to 100% using the "LED charge status" indicator on the Waveshare power manager unit.
    • Measured the battery's voltage using a multimeter for an initial baseline.

  2. Ran the Data Logger Under Normal Load:

    • Configured the data logger to record data at the standard sampling rate of 30-minute intervals.
    • Ensured that all sensors were running simultaneously to simulate real-world conditions:
      • 3 x DS18B20 temperature sensors
      • 3 x SHT30 humidity/temperature sensors
    • Used Wi-Fi to transmit data to the cloud during the test.

  3. Monitored Battery Status:

    • Continuously monitored the battery level throughout the test using the system's battery tracking feature.
    • Logged the battery percentage at regular intervals and tracked its decrease over time.
    • Periodically validated the battery readings by using a multimeter to measure the system's voltage, ensuring accurate voltage measurements.

  4. Test Duration:

    • Let the system run until the battery voltage reached 3.2V (the lowest safe voltage before potentially damaging the battery).
    • Test Conditions: Conducted tests in two different environments:
      • Indoor conditions with relatively stable temperature (~15°C)
      • Outdoor conditions under typical operating conditions in Germany (March 8th, 2025)

  5. Recorded Findings:

    • Documented Conditions: Recorded temperature and humidity data from the sensors.
      • Indoor or Outdoor: Noted the treatment type (Indoor/Outdoor).
      • Time: Used datetime stamps of data logs to calculate battery runtime.
      • Unit Voltage: Recorded the voltage from the voltage divider on the unit.
      • Actual Voltage: Measured voltage periodically with a multimeter at the same time as it was being read by the unit.

  6. Post-Test Analysis:

    • Evaluated Performance: Compared the battery life across both test conditions and noted any temperature variances.
    • Identified Efficiency Improvements: Analyzed components that may have consumed more power than anticipated (e.g., sensors, Wi-Fi module, or data storage).

Results

1. Overview of Test Setup

  • Data Logger Configuration: The data logger was set to record data at 30-minute intervals, using 3 x DS18B20 temperature sensors and 3 x SHT30 humidity/temperature sensors. Data was transmitted to the cloud via Wi-Fi.
  • Test Conditions: Two testing environments were used:
    • Indoor: Stable temperature (~15°C)
    • Outdoor: Normal operating conditions in Germany (March 8th, 2025)
  • Battery Monitoring: Battery voltage read from the voltage divider was monitored , with periodic validation using a multimeter.

2. Battery Runtime

Indoor Test Duration

  • Start Voltage: 3.92 V (actual: 3.96 V)
  • End Voltage: 3.00 V (actual: 3.00 V)
  • Total Runtime: 71.2 hours

Key Observations

  • The internal voltage reading is approximately 0.02 V lower than the multimeter reading at its maximum value.
  • Significant noise is present, likely due to the ADC on the Raspberry Pi Pico, causing fluctuations of around ±0.2 V.
  • While the general trend of the internal voltage reading is accurate, it is not reliable for low-power shutoff decisions.
  • The Waveshare power manager automatically cuts power at 3.0 V.
  • Outdoor Test Duration:

    • Start Voltage: 4.0 V

    • End Voltage: 3.0V

    • Total Runtime: 63.2 H

    • Key Observations

    • The colder average temperatrure reduced run time by approx. 10 hours.

Voltage vs Time Temperature Plot

3. Recharging Process

Starting volatge: 3.0V

Day 1 - 100% cloud Recharging Time: 0.4 V in 7.5 hours = 0.053 V / H

Day 2 - 10% cloud Recharging Time: 0.84 V in 9.5 hours = 0.088 V / H

  • Comments: Happy with recharge effectivness, particularly on day 1 with 100% cloud.

Recharge_time

7. Conclusion

The battery life tests provided valuable insight into the data logger's real-world power performance and highlighted both strengths and areas for optimization.

  • Runtime Observations:

    • Indoors, the logger maintained full functionality for over 71 hours, indicating strong performance under thermally stable conditions.
    • Outdoors, runtime dropped to 63.2 hours, confirming that colder ambient temperatures reduce battery efficiency by approximately 10 hours, consistent with expectations for Li-ion cells.

  • Voltage Monitoring:

    • The internal ADC-based voltage readings from the Pico were generally useful for trend analysis but not sufficiently accurate for determining low-voltage cutoffs due to ±0.2 V fluctuation.
    • External multimeter readings confirmed that the Waveshare power manager reliably cut off at 3.0 V, protecting the battery from over-discharge.

  • Recharging Insights:

    • The system recharged effectively even under 100% cloud cover, gaining 0.4 V over 7.5 hours.
    • On a mostly clear day (10% cloud), recharge rate improved to 0.088 V/hour, reaffirming the suitability of the solar panel and power management system for off-grid use.

  • General Performance:

    • The combination of low-frequency sampling (30 min intervals) and hardware-level power control allowed the unit to perform as intended, with multi-day operation feasible between charges.
    • These results confirm the logger is well-suited for short-term deployments (2.5–3 days) on battery alone, and indefinite operation is possible with moderate solar exposure.

Overall, the test confirms the data logger is capable of sustained autonomous operation under real-world conditions and is suitable for deployment in field-based microclimate studies.