Supercapacitor modules frequently asked questions

Supercapacitors offer higher power densities, longer lifetimes and cycle lifes, require virtually no maintenance, inherently safe operation and have wide operating temperatures. All of these features combine for lower total cost of ownership in applications requiring high power and/or short runtimes.

While both technologies are better suited toward high power and/or short runtime applications, supercapacitors provide much higher reliability, higher energy efficiency, require no serviceable parts to lower maintenance costs. These lower operations costs, combined with lower up front acquisition costs, provide much lower total cost of ownership. 

Supercapacitor construction leverages highly porous carbon materials to form electrodes that store electric charge electrostatically on its surface area. The electrode material offers a surface area of up to 3000 m²/g, which gives supercapacitors their ultra-high capacitance.  

Supercapacitors can be wired in series to form a higher voltage string, wired in parallel for additional capacitance or both, depending on the application. Eaton’s supercapacitors can be wired in series for integration into equipment and systems up to 1500 Vdc. There is virtually no limit to how many can be wired in parallel. 

First, you will need to know the following specifications for your application:

• Constant current or constant power required
• Duration of current or power required
• Acceptable voltage window (max, operating/float and min voltage)

From there, the number of supercapacitors in series needed to accommodate the voltage window would be established. Then the number of strings in parallel is determined based on the amount of energy required to support the load required.

Life of supercapacitors is most often measured in calendar years and is dependent on two primary factors: voltage and temperature. As with any electrical energy storage, higher charge voltages and higher temperatures shorten the life. In a backup power application, a 10-15% derating for the float voltage and a 25 °C ambient temperature can result in lifetimes up to 20 years. Cycle life is another life measurement and can provide millions of charge/discharge cycles.

Supercapacitors are made from light weight, commercially available materials that are RoHS compliant. They do not contain any conflict minerals or pose any recycling issues. Refer to the application guidelines note for more information.  

Any maintenance requirements would the same as basic electrical connections. This would include ensuring cleanliness and checking to ensure proper torque connections annually.  

Use the formula below for calculations:

• Energy stored in Watt-seconds = ½ * C * V²
• Peak power = V² / (4 * ESR)

The possible operating voltage extends from the maximum rated voltage down to 0 volts. The application operating voltage range does impact life expectancy. See the "What is the life of supercapacitors?" section for more information on voltage and lifetime.

There is no practical limit to the recharge capability for supercapacitors. They can be recharged just as fast as they can be discharged. Thus, the power rating of the recharging equipment, rectifier or DC-DC converter, is typically the limiting factor. The pulse current or maximum current listed on respective datasheet can highlight the high-power density.

SOC refers to the amount of stored energy compared to the maximum that can be stored. This parameter is quite easy to determine for supercapacitors in contrast to batteries. Stored energy is proportional to the square of the voltage (Stored energy = ½ capacitance x Voltage²). The state of charge is calculated as the square of the measured voltage divided by the square of the design voltage. For example, a system designed with a float voltage of 480 V is currently at 400 V. This would be a state of charge of 69 percent.  

The operating temperature range of Eaton’s modules are between -40 °C to +65 °C. Depending on the individual module, further voltage derating can be done up to +85 °C.

Efficiency can be evaluated as two different figures. The first would be leakage current/self discharge when float charged. This varies by product and depends on the balancing scheme, specifically for modules. Please consult the individual data sheets for this information. The other would be through cycling and defined as round trip efficiency. The typical round-trip efficiency is greater than 98%.    

Yes. Pairing supercapacitors with batteries to create a hybrid energy storage system (HESS) can provide an optimal energy storage solution in terms of energy density, power density and overall system lifetime that helps improve total cost of ownership. Existing applications have integrated in a passive configuration by placing the two technologies directly in parallel or in an active system which uses a multiple input Power Conditioning System (PCS). 

In UPS applications where there is a generator tied into the power distribution system, ensuring reliable generator startup will be imperative in those mission critical applications. Many modern generators are capable of startup within 10 seconds. This startup reliability is maintained through regular maintenance and testing of the generator. It is a common misconception that over 10 minutes of battery runtime will provide enough time to diagnose and fix a generator that has startup issues. Many mechanics will confirm that if a generator doesn’t start in the first one to two cranks, those 15 minutes of runtime will not be sufficient.  

Through various application testing and evaluation, Eaton has not experienced ripple currents that contribute to a substantial heating effect as can be seen with electrolytic capacitors. Higher ripple currents at lower frequency would be more likely to contribute to any heating effect.   

While both store charge electrostatically, the materials used to do so are different. Traditional capacitors generally use flat plates to store charge. The greater the surface area, the higher the capacitance, which tends to lead to larger sizes. With supercapacitors, the materials used to store charge offer a much higher surface area. This high surface area can store more electric charge, leading to very high capacitances in a much smaller package.

There are no differences between these names. Different manufacturers have used the names to describe their products while EDLC is the generic name.

The failure mode of supercapacitors is a premature end of life condition where the product will degrade to a virtual open circuit. There are no short circuit or other catastrophic failure modes. 

Supercapacitors are transported fully discharged. At initial installation or commissioning, they will be at 0 V. Therefore, a precharge circuit may be needed to reduce inrush currents as supercapacitors can appear to be a short circuit due to their inherently low ESR. Also, the rectifier, PCS or power electronics may accommodate firmware changes to slow ramp up voltage during initial charging to help reduce the inrush currents.