How to observe System Voltage when using LiFePO4 3.2V batteries
When monitoring system voltages, it is recommended, to do so at night when no charging voltage is
applied. The system can record maximum, average, and minimum voltages, which provide insights into the battery’s state of charge and overall health.
Key Points on Voltage Readings
1. Maximum Voltage
Maximum voltage (Value recorded when the system is not under charge and draws the least power from the batteries) may indicate the state of charge (SoC) of the batteries.
This value can be used to set alarm limits (chosen from the table below) to warn about a depleted battery.
State of Charge Guidelines:
Voltage reading Battery rest capacity
3.1V <5%
3.2V <20%
3.25V <50%
3.3V <90%
3.4V 100%
In normal operation, the maximum voltage should be 3.25V or higher.
Note: In battery-only systems (without charging facility like a solar panel) the internal parameter “rest capacity” can be used to monitor battery state.
A daily decreasing trend in maximum voltage may indicate insufficient solar panel output due to:
– Dark weather conditions.
– Damaged, obstructed, or poorly positioned solar panels.
– Excessive power consumption by the application, exceeding the solar panel’s capacity.
Note: Time-out’s (WDT) during sensor readings, are causing excessive power consumption.
2. Minimum Voltage
This value is recorded when the system draws the most current from the batteries, e.g., when the modem is switched on.
Together with the Average voltage, it reflects the system’s battery health.
3. Average Voltage
The Average voltage is calculated and recorded during the system uptime.
– If the Average voltage is closer to the Minimum voltage than the Maximum voltage, it may
Indicate deteriorated Batteries.
– Batteries cannot supply sufficient current, causing voltage dips.
Resolution: Replace the batteries.
Faulty Power Cable:
– Corroded contacts or damaged cables result in high transition resistance and voltage drops
during high loads.
Resolution: Replace the power cable.
Poor Network coverage:
– In areas with poor network coverage (especially during fallback to 2G), excessive current draw
can cause voltage dips.
Resolution: Use a better external antenna.
Risks of Voltage Dips:
– When voltage dips occur suddenly and frequently during modem activity, they will pose a risk of permanent modem malfunction.
Resolution: The firmware has a modem protection routine.
– The modem will not switch on if the Maximum voltage is below 3.15V.
– If voltage dips are detected while the maximum voltage remains above 3.15V, the modem will adjust its operational thresholds. After resolving the issues causing voltage dips (like insufficient solar power) and performing a system power cycle, the thresholds will be reset to the original level of 3.15V.