US How a supercapacitor works
A supercapacitor is a capacitor with a capacitance thousands of times higher than a conventional one, measured in farads rather than microfarads. It sits between an ordinary capacitor and a battery: it stores much more energy than the first and delivers it much faster than the second.
The common type is the electric double-layer capacitor (EDLC). Each cell has two electrodes coated with activated carbon, an electrolyte and a thin porous separator between them. Activated carbon is riddled with tiny pores, so a few grams can have a surface area of well over a thousand square meters. When a voltage is applied, ions in the electrolyte gather at the surface of each electrode, forming a charged layer only a few molecules thick. That enormous area and tiny separation are what give the high capacitance.
Because the charge is stored physically rather than by a chemical reaction, nothing in the electrode wears out as it would in a battery. That is why a supercapacitor can be charged and discharged so quickly and so many times.
Types of supercapacitor
Supercapacitors are grouped by how they store charge, which sets the balance between energy, power and life.
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Double-layer capacitors (EDLC). Carbon electrodes storing charge purely in the double layer. The longest life and the widest temperature range, and the type used in most industrial power backup.
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Pseudocapacitors. Electrodes of metal oxides or conducting polymers add fast surface chemical reactions, raising energy density at some cost in cycle life.
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Hybrid and lithium-ion capacitors. One battery-like electrode and one capacitor electrode. They store several times more energy than an EDLC and charge quickly, but need more careful handling of voltage and temperature.
Supercapacitors compared with batteries and capacitors
The real choice is usually between a supercapacitor and a lithium-ion battery, and they suit different jobs. A battery holds much more energy for its size and weight. A supercapacitor delivers power faster, takes a charge in seconds, tolerates cold and needs no replacement over the life of most systems.
| Property | Supercapacitor (EDLC) | Lithium-ion battery | Electrolytic capacitor |
|---|---|---|---|
| Storage method | Ions in an electric double layer | Chemical reaction | Dielectric film |
| Energy density | Low, typically 5–10 Wh/kg | High, typically 150–250 Wh/kg | Very low |
| Charge time | Seconds | Typically 1–3 hours | Milliseconds |
| Cycle life | Typically 500,000 or more | Typically 500–3,000 | Effectively unlimited |
| Low temperature | Works to about −40 °C | Charging limited below about 0 °C | Works to about −40 °C |
| Self-discharge | Days to weeks | Months | Fast |
| Main risk | Overvoltage per cell | Thermal runaway if damaged | Dries out over years |
The figures are typical ranges and vary by chemistry and manufacturer. The pattern is consistent: supercapacitors trade energy for power, life and temperature range.
For sizing a ride-through supply for a vehicle or rail computer, see our supercapacitor vs battery UPS guide.
Where supercapacitors are used
Supercapacitors fit wherever energy is needed in short bursts, or where a battery would wear out or struggle with heat and cold.
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Power backup and safe shutdown. Keeping a computer running through brief supply dips, and giving it time to save data and shut down cleanly when power is lost.
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Transport and regenerative braking. Capturing braking energy in trams, buses and cranes and releasing it on the next acceleration.
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Dashcams and data loggers. Holding enough charge to close the last file when the ignition goes off, without a battery swelling in a hot windscreen.
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Memory and clock backup. Small coin-style cells keep real-time clocks and configuration memory alive between power cycles.
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Grid and renewables. Smoothing short fluctuations from wind and solar generation and supporting frequency response.
Supercapacitor UPS for industrial computers
A sudden power loss is a risk for any computer writing to storage: files can be left half written and, in the worst case, an operating system image can be corrupted. Vehicle and rail supplies make it worse, dropping out for a moment at cranking, at points and at level crossings. A supercapacitor uninterruptible power supply (UPS) sits between the supply and the computer, rides through those short interruptions and, if power does not return, signals the computer to shut down before its stored energy runs out.
Supercapacitor UPS modules are rated in watt-seconds (joules), the energy they hold. Dividing that by the load gives a rough hold-up time: around 9,000 W·s supports a 100 W computer for about a minute and a half, before conversion losses and the cut-off voltage are taken into account. That is plenty for a clean shutdown, not for running through a long outage. Industrial SSDs apply the same idea on a smaller scale, with onboard capacitors that provide power-loss protection for the data in flight.
Our industrial UPS range includes supercapacitor modules from 2,580 to 9,250 W·s, with DIN-rail, ignition-controlled and 110 V DC railway versions. Some of our EN 50155 railway computers build the supercapacitor UPS into the chassis. Our end-of-train telemetry project with supercapacitor backup shows the approach on freight rolling stock.
Quick answers on supercapacitors
Supercapacitors: common questions
Is a supercapacitor the same as an ultracapacitor?
Yes. Supercapacitor, ultracapacitor and electric double-layer capacitor (EDLC) are used for the same family of devices. Some manufacturers use their own trade names.
Can a supercapacitor replace a battery?
Only where the energy needed is small. A supercapacitor suits bursts of power and short backup times. For hours of runtime, a battery still stores far more energy for its size.
How long can a supercapacitor hold a charge?
Days to weeks, depending on type and temperature. Self-discharge is much faster than in a battery, so a supercapacitor UPS is kept topped up by the supply while the system runs.
How long do supercapacitors last?
Typically 10 years or more in service. Life is set mainly by temperature and voltage. Running a cell below its rated voltage and away from heat extends it.
Why do dashcams use supercapacitors?
Because they tolerate heat better than lithium-ion batteries. A car parked in the sun can get very hot inside, and a supercapacitor holds just enough charge to save the last recording safely.
We specify supercapacitor UPS modules alongside the computer as standard where the supply is unreliable, wire the shutdown signal and set the hold-up and shutdown timings to suit the vehicle or site.