A balancing system is essential in supercapacitors to prevent individual cells in a series connection from being overloaded. In a technical article, René Kalbitz from Würth Elektronik explains the theoretical background of different balancing methods and demonstrates their effectiveness through measurements and practical comparisons. The content is published with permission from Würth Elektronik.
Supercapacitors (SC) typically operate at relatively low voltages of around 2.7 V. To reach higher operating voltages, multiple cells must be connected in series. However, due to manufacturing tolerances or aging effects, differences in capacitance and insulation resistance can cause individual cells to exceed their rated voltage limit. Without proper balancing, this can accelerate aging and lead to premature failures.
This series of notes introduces the principle of unequal voltage distribution in cascaded cells. For simplicity, we use a two-capacitor series stack as an example (any system can be reduced to this equivalent circuit). From there, we review the theoretical background, present real measurements, and analyze practical examples. The aim is to give developers a clear overview of balancing strategies, so they can choose and adapt the most suitable approach for their specific requirements.
Supercapacitor Balancing Guide – Contents
1. Theoretical background of supercapacitor balancing
You can learn more about the theoretical background of supercapacitor balancing. This part delves into the principles of balancing currents and times in capacitors, particularly when considering their tolerance ranges. It provides equations to estimate the necessary current to equalize voltage differences between capacitors in series. For instance, with a nominal capacitance (Cr) of 10F and a tolerance range of -10% to +30%, the actual capacitances could be 9F and 13F. The article emphasizes the importance of calculating the appropriate balancing current and time to ensure efficient capacitor performance.
2. Supercapacitors balancing strategies
For a detailed comparison of methods, visit our post on supercapacitor balancing strategies. Supercapacitors connected in series require balancing strategies to address voltage imbalances caused by variations in capacitance and insulation resistance. These strategies are categorized into passive methods, such as resistors and Zener diodes, which are simple and cost-effective but may result in slower balancing and higher power dissipation, and active methods, like op-amps and MOSFETs, which provide faster and more efficient balancing but are more complex and expensive. The choice of balancing method depends on the specific application’s requirements for speed, power efficiency, and cost.
3. Practical Measurements of Balancing Methods
In our dedicated article on practical measurements of supercapacitor balancing methods, we examine various methods for measuring and balancing voltages in supercapacitors, particularly when connected in series. It discusses passive balancing techniques, such as using resistors and Zener diodes, highlighting their simplicity and cost-effectiveness, though noting potential drawbacks like increased power dissipation and slower balancing times. The article also explores active balancing methods, including the use of operational amplifiers and DC-DC converters, which offer improved balancing efficiency and reduced energy losses but come with added complexity and cost. Through practical measurements and evaluations, the article provides insights into the effectiveness of these balancing strategies, aiding in the selection of appropriate methods for specific applications.
4. Best Supercapacitor Balancing Method – Final Comparison
Finally, our post on the best supercapacitor balancing method evaluates various supercapacitor balancing methods, analyzing their balancing speed, power dissipation, and cost-effectiveness. Passive methods, such as resistor balancing, are noted for their simplicity and low cost but offer slower balancing speeds. Active methods, including those utilizing operational amplifiers (OP-AMPs) and DC-DC converters, provide faster balancing but may involve higher power dissipation and increased complexity. The article emphasizes that selecting the optimal balancing strategy depends on specific application requirements, considering factors like availability, lifetime, and design-in time.
