Selecting the right outdoor data logger battery chemistry is crucial to ensure reliable operation and longevity. Engineers must weigh factors such as energy density, operating temperature range, cycle life, and cost. Among the array of choices, lead-acid batteries often emerge as a preferred solution due to their robustness and cost-effectiveness, but they necessitate careful management to mitigate potential issues. Additionally, alternative chemistries like nickel-cadmium (Ni-Cd), nickel-metal hydride (Ni-MH), and lithium-ion (Li-ion) offer their own advantages and considerations.
Lead-Acid Batteries: The Classic Choice
Lead-acid batteries have long been a staple in applications requiring dependable power sources. Their chemistry offers several advantages ideal for outdoor data loggers such as the FusionDAQ MI-8. These batteries excel in providing consistent power output over extended periods, making them suitable for continuous monitoring applications. Furthermore, lead-acid batteries are relatively inexpensive compared to alternatives, which is advantageous for projects with budget constraints.
However, despite their reliability, lead-acid batteries still require care in freezing or extreme temperature environments. As the battery is discharged the electrolyte freezing temperature increases. In practice this means a lead-acid battery should not be discharged below 50% below 0°C. A battery management or protection circuit is often employed to protect the battery in these conditions.
Alternative Chemistries: Ni-Cd, Ni-MH, and Li-ion
Ni-Cd and Ni-MH batteries offer alternatives to lead-acid with distinct characteristics. Ni-Cd batteries provide good cycle life and tolerance to overcharge. Ni-MH batteries, on the other hand, offer higher energy density and reduced environmental impact compared to Ni-Cd.
While Ni-Cd and Ni-MH batteries exhibit favorable attributes, they also have limitations. Ni-Cd batteries suffer from the memory effect, where capacity decreases if not fully discharged before recharging. Ni-MH batteries, while offering higher energy density than Ni-Cd, are susceptible to self-discharge over time.
Li-ion batteries stand out for their superior energy density, making them ideal for applications where weight and space are critical considerations. However, they have a limited working temperature range and are not suitable for freezing conditions or extreme heat. Additionally, Li-ion batteries require sophisticated battery management systems to protect against overcharge and over-discharge, adding complexity to system design.
In recent years, inexpensive self-contained Li-ion battery packs have become increasing popular, especially for charging cell phones and consumer electronics. These packs are compact and work great at room temperature, but they are rarely designed to withstand outdoor temperature ranges.
In any installation, always consider the operating temperatures of whichever battery technology is selected. Also note that the temperate range where a battery may be charged is generally smaller than the full operating envelope. For example, specially designed Li-Ion batteries exist to allow charging below freezing, but their charging rate is so limited that it may take more the 50 hours to completely charge. BatteryUniversity.com is an excellent resource for more information
| Battery Chemistry | Operating Temperature Range |
| Lead-Acid (Pb-Acid) | -20°C to 50°C |
| Nickel-Metal Hydride (Ni-MH) | -20°C to 50°C |
| Nickel-Cadmium (Ni-Cd) | -20°C to 45°C |
| Lithium-Ion (Li-ion) | 15°C to 35°C |
Conclusion
By understanding the unique characteristics of each battery chemistry and considering factors such as operating temperature range and cost, engineers can make informed decisions when selecting power sources for outdoor data loggers. While lead-acid batteries remain a popular choice due to their reliability and cost-effectiveness, alternative chemistries like Ni-Cd, Ni-MH, and Li-ion offer viable options with their own set of advantages and considerations.
Whether looking for design advice or a complete technical solution FusionDAQ’s team is here to help build your next outdoor data logging solution.