energy storage

5 Valuable Insights About ESR and ESL in Supercapacitors You Need to Know

Supercapacitors prioritize efficiency, and that’s where ESR plays a critical role. Think of ESR as the key factor that ensures smooth operation by reducing heat and energy loss during high-demand charge and discharge cycles. Lower ESR enhances the reliability and efficiency of your supercapacitor, helping to prevent issues like overheating and accelerated degradation. On the flip side, high ESR can lead to wasted energy and overheating—definitely something to avoid. Understanding and minimizing ESR and ESL are key to optimizing the balance between energy storage, power delivery, and longevity in supercapacitor-based systems.

1. What is ESR, and Why Does Low ESR Matter in Supercapacitors?


ESR measures a supercapacitor’s efficiency in charging and discharging. The lower the ESR, the fewer thermal losses occur. Since supercapacitors can handle extremely high currents (up to tens of kiloamps), a high ESR would cause rapid heating, leading to faster degradation and even safety risks. To avoid these issues, keeping ESR as low as possible is crucial for maintaining product performance and safety.

Psst!  Don't miss our earlier blog article on this topic: What is ESR and Why It Matters


2. What’s the Difference Between ESR and ESL?


Supercapacitors experience thermal losses in both ESR and ESL. These two components are what make up the ultimate description for a supercapacitor’s behavior under current: impedance. 

In simple designs utilizing relatively low currents and Direct Current (DC), the ESL value is small enough to be neglected in calculations. However, whereas ESR describes the resistance to current flow, ESL describes the resistance to current value. In applications where the value of applied current changes very fast (imagine going from 0 A to 1000 A in milliseconds) or where the direction of the current changes rapidly (Alternating Current, AC) ESL value must be considered as well.



3. How Does Low ESR Improve Supercapacitor Performance?

 

  • Higher Power Density: A lower ESR increases power density, enabling the supercapacitor to deliver more power in short bursts, crucial for applications like regenerative braking where energy needs to be delivered quickly.

 

  • Reduced Power Loss:  Lower ESR minimizes power lost as heat, boosting overall efficiency, particularly in rapid charge-discharge cycles.

 

  • Better Thermal Management: High ESR generates more heat during operation, potentially damaging the device and shortening its lifespan. A lower ESR allows for better thermal performance, reducing the need for multiple supercapacitors to achieve high currents.


4. How Do You Choose the Right ESR for a Supercapacitor?


The optimal ESR depends on the application. Ideally, ESR would be zero—resulting in no thermal losses or self-heating.

However, the rest of the infrastructure besides the supercapacitors themselves in systems must be considered. As the ESR of supercapacitors gets closer and closer to zero, the potential currents reached in the system also go higher and higher. This brings considerations like the thermal capabilities of connections and the effects of magnetic forces at fast changes in current into play. 

In practice, ESR should be as low as possible without compromising the system’s overall integrity. This decision needs to be made on a case-by-case basis.



5. What Happens When ESR is Too High?


If a supercapacitor has a high ESR, it directly translates to significant energy losses within the circuit. All the electric potential energy needs to go somewhere, and the main component by far is thermal energy.  

A supercapacitor with a high ESR will heat up significantly more in applications that a supercapacitor with a low ESR, and the issue will get more pronounced as the currents go higher. First and foremost it is a problem for the longevity of the product, as the supercapacitors age faster at higher temperatures. In more acute situations, the supercapacitors would heat up beyond the allowed temperature range, which would result in either forced shutdown of the system or risking the safety of operation.

 


Key Abbreviations

ESR (Equivalent Series Resistance) and ESL (Equivalent Series Inductance) are crucial electrical parameters that impact supercapacitor performance. Considering these factors is essential for designing high-performance supercapacitors that meet the demands of modern energy storage and power delivery systems.

 

  • ESR (Equivalent Series Resistance) 

    ESR refers to the internal resistance within a supercapacitor that causes energy loss in the form of heat during charge and discharge cycles. In simple terms, it’s the "hidden" resistance that impairs the efficiency of energy storage devices.

    Why It Matters: A low ESR is essential for minimizing power losses, improving energy efficiency, and preventing excess heat generation. If ESR is too high, energy is wasted as heat, and the device can overheat or degrade more quickly, reducing its lifespan and performance.


  • ESL (Equivalent Series Inductance) 

    ESL is the parasitic inductance within a supercapacitor, which becomes significant when dealing with rapidly changing currents. It’s the component's resistance to changes in current, especially in high-frequency applications.

    Why It Matters: Low ESL is important for maintaining performance in applications where the current changes quickly (such as in high-frequency circuits or switching power supplies). High ESL can lead to inefficient energy transfer and limit the response time of the device.

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