Supercapacitor Symbol
Definition: The Supercapacitor symbol represents an electric double-layer capacitor (EDLC) — a polarised energy-storage device that stores charge electrostatically at the electrode–electrolyte interface rather than in a dielectric, offering capacitances from farads to thousands of farads at low voltages (typically 2.5–2.7 V per cell), as standardised in IEC 62391 and depicted using the polarised capacitor symbol convention of IEC 60617.
Also known as: ultracapacitor, EDLC, electric double-layer capacitor, Goldcap, supercap, electrochemical capacitor.
What the Supercapacitor symbol means
The supercapacitor symbol denotes a high-capacitance, low-voltage energy-storage component that bridges the gap between conventional capacitors and rechargeable batteries. Unlike a standard electrolytic capacitor that stores charge in a dielectric layer, a supercapacitor stores energy at the interface between a high-surface-area electrode (typically activated carbon) and a liquid electrolyte, achieving capacitances millions of times larger than ceramic or film capacitors.
In circuit diagrams, the supercapacitor symbol signals an energy-buffering role: the device charges rapidly from a power source and then delivers bursts of current to a load without the slow charge-cycle limitations of batteries. It is polarised — the positive terminal (+) must connect to the more-positive circuit potential — and is rated for a specific maximum voltage per cell, requiring series-cell balancing when stacked to higher voltages.
How to identify the Supercapacitor symbol
The supercapacitor symbol is drawn as two parallel vertical lines (resembling a standard non-polarised capacitor), but one plate is typically drawn with a curved line (like a polarised electrolytic capacitor) and a plus sign (+) marks the positive terminal at the top. Some schematic conventions add a second curved plate or a distinctive wave line on one plate to differentiate it from a simple electrolytic capacitor. The positive pin (+) appears at the top and the negative pin (−) at the bottom.
Function and usage boundary
A supercapacitor stores and releases electrical energy through rapid surface-charge accumulation at high-surface-area electrodes, delivering high peak currents for short durations. It excels at energy buffering — smoothing voltage dips during load transients, providing backup power during brief power interruptions, capturing regenerative braking energy, and supplying starting pulses for motors or transmitters. It complements batteries by handling high-power, short-duration events that would otherwise degrade battery cycle life.
Standards: IEC vs ANSI
| IEC 60617 | IEC 62391 (Fixed electric double-layer capacitors for use in electronic equipment) defines supercapacitor performance, test methods, and marking; IEC 60617 depicts the symbol as a polarised capacitor variant — two parallel plates with a curved negative plate and a + polarity marking. |
|---|---|
| ANSI/IEEE 315 | IEEE / ANSI Y32.2 does not define a dedicated supercapacitor glyph; North American practice uses the same polarised capacitor symbol with a 'SC' or 'C' designator and a capacitance value in farads (F) to indicate a supercapacitor. |
| Key difference | IEC and ANSI both use the polarised capacitor symbol shape for supercapacitors; the distinction from a standard electrolytic capacitor is conveyed by the component label (EDLC, SC, or a value in farads) and component designation letter rather than a unique glyph. Some CAD libraries add a distinctive curved second plate to signal EDLC type. |
The displayed SVG is the live editor implementation, not a licensed reproduction or certification of an IEC or IEEE database glyph. Verify the exact official entry and project edition before issuing work.
Logical terminals
| Logical ID | Editor terminal name |
|---|---|
| pos | + |
| neg | - |
Where the Supercapacitor symbol is used
- Backup power for real-time clock (RTC) ICs and SRAM in embedded systems during battery replacement
- Regenerative braking energy capture in hybrid and electric vehicles and trams
- Peak-power buffering for GPS and cellular radio transmitters (burst-current demands)
- Engine start-assist systems where cold batteries cannot supply sufficient cranking current
- Smart meters providing hold-up power during power interruptions to complete data logging
- Industrial UPS systems bridging the gap between power failure detection and generator start-up
- Wearable electronics smoothing energy harvesting from piezoelectric or solar cells
Key facts
- A supercapacitor (EDLC, ultracapacitor) stores charge at the electrode-electrolyte interface, achieving capacitances of 0.1 F to 3000 F — millions of times larger than ceramic capacitors — per IEC 62391.
- The supercapacitor symbol uses the polarised capacitor glyph (two parallel plates, one curved, with a + polarity marker) per IEC 60617 convention; designator letter is C.
- The positive terminal (+) is marked at pin 'pos' and must connect to the more-positive circuit potential; reversing polarity can permanently damage or rupture the cell.
- Supercapacitors have energy density of 1–15 Wh/kg but power density of 1–10 kW/kg, making them complementary to batteries rather than replacements — ideal for high-power short-duration applications.
- Individual cell voltage is limited to 2.5–2.85 V (aqueous electrolyte) or up to 3.8 V (organic); series stacking with cell-balancing circuits is required to reach higher system voltages.
- Equivalent Series Resistance (ESR) of a supercapacitor is very low (0.1 mΩ to 100 mΩ), enabling very high peak discharge currents compared to batteries of similar energy capacity.
- Cycle life exceeds 500,000 to 1,000,000 charge-discharge cycles — orders of magnitude greater than lithium-ion batteries — making supercapacitors ideal for applications with frequent energy cycling.
Frequently asked questions
What does the supercapacitor symbol mean in a circuit diagram?
The supercapacitor symbol represents an electric double-layer capacitor (EDLC) — a high-capacitance polarised energy-storage device that rapidly stores and releases energy. It indicates an energy-buffering component that handles peak current demands or backup power needs. The symbol is a polarised capacitor variant with a + marker at the positive terminal (top pin) and a curved negative plate.
What does the supercapacitor symbol look like?
The supercapacitor symbol looks like a polarised electrolytic capacitor symbol: two parallel plates, with the negative plate drawn as a curved line and a + polarity marker at the positive terminal. In some CAD libraries, both plates are curved or a distinctive wavy line is used on one plate to distinguish the supercapacitor from a standard electrolytic. The designator is C with a value in farads (F).
What is the difference between a supercapacitor and an electrolytic capacitor?
An electrolytic capacitor stores charge in a thin oxide dielectric layer and has capacitances typically up to 10,000 µF (0.01 F) with voltage ratings to hundreds of volts. A supercapacitor stores charge electrostatically at the electrode-electrolyte surface interface, achieving capacitances from 0.1 F to 3000 F but at much lower voltages (2.5–2.85 V per cell). Supercapacitors also have far longer cycle lives (>500,000 cycles) compared to electrolytic capacitors in power-cycling applications.
What standard defines the supercapacitor?
IEC 62391 (Fixed electric double-layer capacitors for use in electronic equipment) defines supercapacitor characteristics, ratings, and test methods. The symbol in schematic diagrams follows the IEC 60617 polarised capacitor convention. ANSI Y32.2 / IEEE 315 does not have a dedicated supercapacitor glyph; North American schematics use the same polarised capacitor symbol with a label indicating EDLC or supercapacitor.
Are supercapacitors polarised?
Yes, most supercapacitors are polarised and must have their positive terminal (+) connected to the more-positive voltage in the circuit. Reversing polarity degrades or destroys the cell. Some symmetric EDLC cells allow limited bipolar operation, but standard commercial supercapacitors should be treated as polarised devices with a marked + terminal.
What is the designator letter for a supercapacitor in schematics?
The designator letter for a supercapacitor is C (the same as all capacitors), per IEC 60617 and IEEE 315 conventions. To distinguish a supercapacitor from a regular capacitor, the designator is written as C with a value in farads (e.g. C1 = 1 F) and the component label may include 'EDLC', 'SC', or 'Supercap'.
What voltage rating do supercapacitors have?
Individual supercapacitor cells are typically rated at 2.5 V to 2.85 V (aqueous electrolyte) or up to 3.8 V (organic electrolyte). To reach higher operating voltages, multiple cells are connected in series with cell-balancing circuits to ensure equal voltage distribution. Common commercial modules combine 2–6 cells to provide 5 V, 8 V, or 16 V rated assemblies.
Related symbols
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