What are Electric Double Layer Capacitors (EDLC)

 

Usage of capacitors is a must in every Embedded application. The capacitor helps to improve the noise performance of a power rail and also acts as a energy bank in applications where the sudden burst of energy is handled. While the normal capacitor with two plates separated by dielectric has low energy density. The energy density is energy per unit mass. While the normal capacitors can be used in many applications, there are several applications like the Electric Vehicles, Solar applications, UPS, devices using flash like the camera which require fast charging and discharging with a good energy density. Electric Double layer capacitors (EDLC) fall under this category where they are used just before the battery such that any instantaneous load or bursts of energy delivery requirements on the battery shall be supported by these capacitors.

Electric Double layer capacitors are also known as Super capacitors or ultra capacitors. EDLC capacitors use special electrodes and electrolyte unlike the dielectric used in normal capacitors. These perform fast charging and discharging and has good life cycles up to 1,000,000. The capacitor values to store such high energies must be high and are in the range of thousands of Farads. EDLC used along with batteries help to acts as standby power sources. However, EDLC capacitors are a costly option. Also, considering the energy density, there are available at lower temperature options unlike the normal capacitors whose operating temperatures can range up to 150 degC. EDLC capacitors have a lower ESR than the batteries are an ideal components to supply bursts and to act as backup option to batteries in many cases. Leakage current is another important specification of this capacitors. The leakage current increases with increase in temperature.

For example, if we consider the EDLC capacitor SCCY1AB857S3PBLE from AVX corporation, it has below characteristics:

• Capacitance of 850F
• Operating Temperature of -40 to +85 degC
• Life Time of 2000 Hrs @ 65°C
• ESR of 1mohm at 1 kHz

Below is the image of another EDLC capacitor from Nichicon.