What is a supercapacitor?
Supercapacitors are energy storage and power delivery devices. They utilize high surface area carbon as the energy storage medium, resulting in an energy density much higher than conventional capacitors, and store their energy as a static charge, resulting in a power density far higher than that of batteries.
Supercapacitors have been in production for many years, but CAP-XX’s proprietary technologies ensure that its products have very low ESR (internal resistance), enabling their use in applications requiring very high pulse currents, such as PDAs & POS terminals, modems & wireless sensors, medical devices, digital cameras & mobile phones, location tracking devices and automated metering systems.
How do supercapacitors and capacitors differ?
A traditional capacitor has three essential parts: two electrical conductors, which are usually metal plates, separated and insulated by a “dielectric”. The plates are charged with equal amounts of positive and negative electrical charge. The greater the area for storing charge (i.e. the surface area of the elecrodes), and the thinner the dielectric (i.e. the distance separating the two charged plates), the greater the capacitance. Note that this is a “physical” storage of electricity, as distinct from the “chemical” storage systems found in batteries.
A supercapacitor differs from a capacitor in that it has a much greater charge storage area, because it utilizes highly porous carbon materials rather than flat plates to store the charge. The carbon used in CAP-XX supercapacitors offers as much as 2,000 square meters of surface area per gram of material. The separation distance between the charged areas is also much less in a supercapacitor, because it uses an electrolyte to conduct the charged ions into the carbon electrode layers, yielding a charge separation distance measured in angstroms.
When would you use a supercapacitor?
A supercapacitor has the advantage that it stores far more energy than a traditional capacitor, yet delivers far more power than a battery or energy harvester. There are 2 main categories of supercapacitor applications:
- Peak Power Support
If the energy source, such as a battery, energy harvester, or remote power supply with long wires adding high impedance can supply the average current or power the load requires, but cannot supply the peak power, then using a supercapacitor overcomes this limitation. The supercapacitor is charged at the average current or power, and supplies the peak power when the load requires it. The supercapacitor has sufficient energy storage to supply the load burst for its duration, and with its low Equivalent Series Resistance (ESR) can deliver the high power required by the load. It is important that the average input power available ≥ average output power, this ensures the supercapacitor will be re-charged between load bursts, otherwise it will eventually be discharged to 0V.
- Backup Power Support
The large energy storage and high power capability of a supercapacitor makes it ideal to provide power backup to maintain a unit’s operation in the event of a power interruption, or to enable a graceful shutdown in the event of power loss. Examples include a POS terminal – if a server drops it mid transaction, the battery contacts may break and make, but the supercapacitor will maintain the terminal’s voltage so the transaction is not corrupted; a smart meter where the supercapacitor provides the energy for a last gasp transmission when the battery fails; an SSD which stores data in cache will be corrupted if there is a power interruption – the supercapacitor provides backup power so the SSD can flush the cache to flash memory and maintain integrity.
What’s the difference between power and energy?
Energy is the amount of work that can be done.
Power is the amount of work that is done over a specific period of time. In other words, power measures how fast energy is transferred.
Power is measured in watts (W), and energy in Joules (J). 1J = 1W.sec.
Are CAP-XX supercapacitors able to be reflow or wave soldered?
CAP-XX supercapacitors are packaged in a soft aluminium laminate pouch with heat sealed edges. While the package is a surface mountable design, it cannot be assembled with wave solder or IR reflow processes. Assembly can be undertaken as a secondary operation, using a manual soldering iron, or automated methods such as hot bar jig, robotic soldering, and selective soldering, provded that the temperature to which the device is exposed does not exceed its rated maximum. More information on handling and asssembly can be found in the CAP-XX Product Guide.
Are CAP-XX supercapacitors environmentally friendly?
Yes. CAP-XX supercapacitors are lead-free and can be transported and recycled without restriction. CAP-XX supercapacitors have no heavy metals, no conflict metals and no halogens. They are UL-certified and RoHS, REACH and WEEE compliant. Refer to the Certifications & Compliances section for more information.
What’s the difference between an ultracapacitor, supercapacitor, and an electrochemical double-layer capacitor (EDLC)?
These are just different names for the same thing. These terms describe a device which uses carbon and an electrolyte as its charge storage medium, with no dielectric. EDLC is the generic name, but most manufacturers use either supercapacitor or ultracapacitor to describe their products.
What is operating life of a supercapacitor versus a battery?
That depends. In applications which experience charge/discharge cycling, a supercapacitor will last 10 – 100 times as long as a secondary (rechargeable) battery.
What is the failure mode of a supercapacitor?
If a supercapacitor is exposed to excessive voltage or temperature for extended periods of time it will gradually degrade to essentially an open circuit condition. The time taken for this to occur depends on how much over-voltage or over-temperature is applied. Other than physically puncturing the supercapacitor, there are no short circuit failure modes. There are no catastrophic failure modes.
Why do supercapacitors have to be voltage balanced?
The balancing requirements for a supercapacitor vary with application and product type so CAP-XX elected not to add internal balancing but to instead work with customers to determine the optimum solution for each system. These solutions range from a simple resistor that is suitable for most systems to an active balance circuit for more demanding applications.
What temperature ranges does CAP-XX offer?
CAP-XX offers a general purpose DMF and G series with an operating temperature range of -40°C to +70°C,and high temperature H series with an extended operating temperature range of -40°C to +85°C and higher voltage rating of 2.75V/cell, and an ultra-long life DMT series with a temperature range of -40°C to +85°C and voltage rating of 4.2V, which is the maximum required for Li-Ion battery applications. CAP-XX does not recommend operating its supercapacitors at or near maximum rated temperature for an extended period of time as it will reduce life and impact on performance.
Can CAP-XX supercapacitors be connected in series to achieve higher voltage?
Yes. The GW2 and GS2 devices are essentially two of the respective devices connected in series to achieve a higher voltage. Please contact our sales team with your requirements.
What is the difference between cylindrical and prismatic supercapacitors?
A prismatic supercapacitor such as CAP-XX produces, consists of a number of layers that are connected in parallel. This results in a flat, very low-ESR device. A cylindrical supercapacitor is “wound” into a roll and while cost effective for larger devices a cylindrical device typically is larger and has higher ESR and inductance.
What is the self-discharge rate and leakage current of CAP-XX supercapacitors?
A fully charged CAP-XX supercapacitor will typically have leakage current of under 1 micro amp. For a multi-cell devices such as the GS2/GW1 series the balance resistors will determine the total leakage rate as the resistors are typically sized such that they have a about 10 times the leakage of the supercapacitor itself. For applications requiring very low leakage CAP-XX’s application team has several active balancing circuits that can cut the total leakage current from the supercapacitor and balance circuit to less than 2 micro amps.
What is the frequency response of CAP-XX supercapacitors?
Typically supercapacitors are used for low-frequency, less than 100Hz, applications but this is not true of all supercapacitors. CAP-XX supercapacitors can be used in pulsed applications such as GPRS and GSM with pulses of 500 µS. In fact, our supercapacitors are still very effective at pulse widths down to 100 µS. CAP-XX has found that a term we call effective capacitance or Ceff is a much better indication than a traditional frequency response plot of supercapacitor behavior in pulse power applications. Ceff reflects the percentage of DC capacitance available at a given pulse width and can be thought of the time domain representation of the frequency response curve. For a 1 millisecond pulse a typical CAP-XX supercapacitor will have approximately 50% of the DC capacitance. Ceff varies with device type and temperature so contact CAP-XX for more information.
What are the key parameters for measuring supercapacitors?
Effective capacitance for a given pulse width
ESR (Equivalent Series Resistance)
Do I need to de-rate a supercapacitor?
No. Supercapacitors are inherently safe. A minor over-voltage event that lasts a few milliseconds will not affect the supercapacitor performance. For example, if a CAP-XX supercapacitor rated at 4.5V was subjected to 5V for a few seconds, there would be no effect on the supercapacitor. You can operate a supercapacitor continuously at its rated voltage.
Do your supercapacitors change size when they are charged or discharged?
No, unlike a battery there are no chemical reactions that can cause our part to change size.
What happens if I reverse bias a supercapacitor?
Even though CAP-XX marks a polarity on our supercapacitors they are inherently a non-polarized device. However, once they have been charged the ions in the electrolyte migrate to the positive and negative electrodes. Reversing polarity causes these ions to migrate across the device and will result in an increase in ESR. There are no safety issues if a supercapacitor is reverse biased, there will be no explosion, fire, smoke, or swelling. All of our supercapacitors go though extensive testing and burn-in at voltage and as part of this process they are polarized in the manner indicated on the part.
What happens if I apply excessive voltage to a supercapacitor?
Supercapacitors are inherently safe. They do not contain any chemicals (such as Li) that may explode. If excessive voltage is applied to a supercapacitor all that will happen is the ESR will increase and the device may swell as a result of the electrolyte breaking down and forming gasses. There will be no explosion, fire or smoke.
Are your parts shipped uncharged?
Yes, the parts are discharged prior to shipment.
Will static electricity damage CAP-XX supercapacitors?
No. The reason for this is that even though static electricity discharges are at thousands of volts there is very little current and thus the charge in coulombs is very low so will not cause a voltage increase that could damage the device. CAP-XX does ship our supercapacitors in anti-static packaging. However, this is not to protect our parts but to eliminate the possibility of our packaging materials generating static electricity when handled at the customer.
How are your parts shipped to customers?
CAP-XX supercapacitors are shipped in stackable anti-static trays, each tray holding 10 devices nested within cavities molded in the tray. These trays are designed so that the devices can be removed from the tray by hand or by vacuum pens.
What should I consider when using a supercapacitor in a circuit?
The main issue when using a supercapacitor is inrush current when charging a discharged supercapacitor. Assume you are using a CAP-XX GW201 supercapacitor (typical ESR = 80mΩ, typical C = 0.3F), and a battery pack at 3.8V with an output impedance = 150m W (typical for a Lithium-ion battery pack with protection circuit). At the instant you connect the supercapacitor across the battery pack the inrush current = 3.8V/(150mΩ + 80mΩ) = 16.5A! The battery protection circuit will shut the battery pack down. After 100msecs the current would have decayed to 3.9A. CAP-XX Application Note 1002 has some current limiting solutions.
Can CAP-XX supercapacitors be damaged by charging too fast?
No. We rate out parts at 30 amps of pulse current so they can be charged at that rate. We do have charge current limit circuits available, but those are to protect the system or battery from excessive current in charging a supercapacitor. For more information, please refer to the previous question (using a supercapacitor in a circuit).
How long does it take to charge a supercapacitor? Are they too big to charge between load pulses?
Supercapacitors average the load as seen by the source, and average the source voltage as seen by the load. The bigger the supercapacitor, the better the averaging. It is a misconception that a supercapacitor is “too big” to charge between pulses. The bigger the supercapacitor, the less it is discharged during the pulse and the less it needs to be charged between pulses. In this case, the supercapacitor acts as a low pass filter. In the case of a pulse train with an ideal supercapacitor with infinite capacitance and zero mΩ ESR, the source will see a DC current = average load current, and the Load will see a DC voltage = Source voltage at no load – source impedance x average load current.
Can CAP-XX supercapacitors be bent or compressed?
The supercapacitor device is hermetically sealed and bending or applying too much pressure on the device may damage the seals leading to device failure. CAP-XX supercapacitors should not be exposed to 400kPa pressure across flat surface of device (10 kg or 22lb max). CAP-XX has worked with customers developing “wearable” devices where some flexing of the device was needed. If you have such a requirement, please contact our sales team.
Does CAP-XX offer engineering services?
Yes, CAP-XX has a seasoned applications team that can assist customers in selection and application of our supercapacitors. There are also many application notes in the resources section of this Web site. Contact our sales team about our engineering services.