SUPERCAPACITOR

CONTENTS What is capacitor Capacitance How charge stored in capacitor Factors affecting capacitance of capacitor Why super capacitor What is super capacitor Comparison between super capacitor and capacitor Types of super capacitor Working of super capacitor Advantages and Disadvantages Applications Conclusion

Capacitor Capacitor is an electronic component that stores electric charge. The capacitor is made of 2 close conductors (usually plates) that are

separated by a dielectric material (waxed paper, mica, ceramic, plastic).

• The plates accumulate electric charge when connected to

power source.

• One plate accumulates positive charge and the other plate

accumulates negative charge.

Capacitance

• The capacitance is the amount of electric charge that is stored in the capacitor at voltage of 1 Volt.

• The capacitance is measured in units of Farad (F)• The capacitance (C) of the capacitor is equal to the electric charge (Q)

divided by the voltage (V)

C=Q/V

C is the capacitance in farad (F)

Q is the electric charge  in coulombs (C), that is stored on the capacitor

V is the voltage between the capacitor's plates in volts (V)

Capacitance of parallel plate capacitor

• The capacitance (C) of the plates capacitor is equal to the permittivity (ε) times the plate area (A) divided by the gap or distance between the plates (d)

C is the capacitance of the capacitor, in farad (F). ε is the permittivity of the capacitor's dialectic

material, in farad per meter (F/m) A is the area of the capacitor's plate in square

meters (m). d is the distance between the capacitor's plates, in

meters (m).

How charge stored in capacitor

• When a voltage is applied to these plates an electrical current flows charging up one plate with a positive charge with respect to the supply voltage and the other plate with an equal and opposite negative charge.

• When a capacitor is fully charged there is a potential difference, p.d. between its plates, and the larger the area of the plates and/or the smaller the distance between them (known as separation) the greater will be the charge that the capacitor can hold and the greater will be its Capacitance.

Factors Affecting Capacitance

• Capacitance can also be determined from the dimensions or area, A of the plates and the properties of the dielectric material between the plates. A measure of the dielectric material is given by the permittivity,(ε),or the dielectric constant. So another way of expressing the capacitance of a capacitor is:

• with Air as its dielectric

• with a Solid as its dielectric

Factors Affecting CapacitancePLATE AREA: greater plate area gives greater capacitance; less plate area gives less capacitance.Explanation: Larger plate area results in more field flux (charge collected on the plates) for a given field force (voltage across the plates)

PLATE SPACING: All other factors being equal, further plate spacing gives less capacitance; closer plate spacing gives greater capacitance.Explanation: Closer spacing results in a greater field force (voltage across the capacitor divided by the distance between the plates), which results in a greater field flux (charge collected on the plates) for any given voltage applied across the plates.

Factors Affecting Capacitance

DIELECTRIC MATERIAL: greater permittivity of the dielectric gives greater capacitance; less permittivity of the dielectric gives less capacitance.

Explanation: Materials with a greater permittivity allow for more field flux (offer less opposition), and thus a greater collected charge, for any given amount of field force (applied voltage).

“Relative” permittivity means the permittivity of a material, relative to that of a pure vacuum. The greater the number, the greater the permittivity of the material. Glass, for instance, with a relative permittivity of 7, has seven times the permittivity of a pure vacuum, and consequently will allow for the establishment of an electric field flux seven times stronger than that of a vacuum, all other factors being equal.

Relative permittivities of various common substances

Why super capacitor Electricity is relatively difficult to store in a hurry.

Batteries can hold large amounts of power.

They take hours to charge up.

Capacitors, on the other hand… charge almost instantly but store only tiny

amounts of energy Then we need to store and release large amounts of electricity very

quickly, it's quite likely we'll turn to supercapacitors (also known as ultra capacitors) that combine the best of both worlds.

Super capacitor Supercapacitors are electrochemical devices with following

features:

High energy density. High power density. High capacitance. Longer life.

A supercapacitor or ultra capacitor is an electrochemical capacitor that has an unusually high energy density when compared to common capacitors. They are of particular interest in automotive applications for hybrid vehicles and as supplementary storage for battery electric vehicles.

• They typically store 10 to 100 times more energy per unit volume or mass than electrolytic capacitors, can accept and deliver charge much faster than batteries, and tolerate many more charge and discharge cycles than rechargeable batteries.

• Supercapacitors are used in applications requiring many rapid charge/discharge cycles rather than long term compact energy storage: within cars, buses, trains, cranes and elevators, where they are used for regenerative braking.

• Supercapacitors do not use the conventional solid dielectric of ordinary capacitors. They use electrostatic double-layer capacitance or electrochemical pseudo capacitance or a combination of both instead

history

• In 1950s General Electric Engineers started experimenting components using porous carbon electrodes for fuel cells and rechargeable batteries.

• In 1957 H. Becker developed a "Low voltage electrolytic capacitor with porous carbon electrodes.(He believed that the energy was stored as a charge in the carbon pores )

• In 1966 researchers at Standard Oil of Ohio (SOHIO) developed another version of the component as "electrical energy storage apparatus", while working on experimental fuel cell designs. The nature of electrochemical energy storage was not described in this patent.

• SOHIO did not commercialize their invention, licensing the technology to NEC, who finally marketed the results as "supercapacitors" in 1971, to provide backup power for computer memory

Principle, construction and workingPrinciple:

Energy is stored in ultra capacitor by polarizing the electrolytic solution. The charges are separated via electrode –electrolyte interface.

Current Collector Electrolyte

Separator

Porous electrode

• Every electrochemical capacitor has two electrodes, mechanically separated by a separator.

• which are ionically connected to each other via the electrolyte• The electrolyte is a mixture of positive and negative ions dissolved

in a solvent such as water.

• At each of the two electrodes surfaces originates an area in which the liquid electrolyte contacts the conductive metallic surface of the electrode.

• This interface forms a common boundary among two different phases of matter.

• In this interface occurs a very special phenomenon of the double layer effect.

Working

• Applying a voltage to an electrochemical capacitor causes both electrodes in the capacitor to generate electrical double-layers.

• The two layers are separated by a monolayer of solvent molecules.

• There for there is a formation of a layer of ions the both side of the plate. This is called ‘double layer’ formation

• For this reason ultracapacitor also known as double layer capacitor

• The distance between the plates is in the order of angstroms

• According to the formula of capacitance,

Dielectric constant of medium X area of the plate capacitance: -------------------------------------------------------------- Distance between the plates

• capacitance C is greatest in capacitors made from materials with a high permittivity, large electrode plate surface areas and small distance between plates d. As a result, double-layer capacitors have much higher capacitance values than conventional capacitors, arising from the extremely large surface area of activated carbon electrodes and the extremely thin double-layer distance on the order of a few angstroms (0.3-0.8 nm).

CHARGING & DISCHARGING

RECAP…..

Types of supercapacitors Supercapacitors are mainly classified into three types:

•Double layer capacitors•Pseudo -capacitors•Hybrid capacitors

Supercapacitor vs CapacitorCAPACITOR SUPER CAPACITOR

DefinitionIn capacitors, energy is stored in their electric field.

A supercapacitor is also known as ultra capacitor or double-layer capacitor. A supercapacitor tends to differ from an ordinary capacitor due to its very high capacitance.

Energy Density Comparatively low Comparatively very high

Cost Comparatively cheap Comparatively expensive

Dielectric materials

Dielectric material like ceramic, polymer films or aluminium oxide are used for the separation of the electrodes.

Activated carbon is used as a physical barrier between the electrodes so that when an electrical charge is applied to the material a double electric field is generated. This electric field acts like a dielectric.

Advantages

• Less Battery Drain – A car’s battery does not deplete due to a capacitor.

• Powerful stereos- Amplifiers and subwoofers working mechanism is based on the capacitors

• Less Damaged equipment – It helps to avoid the excessive drawing of power.

• High energy storage - Compared to conventional capacitor technologies, it possesses orders of magnitude higher energy density.

• Low Equivalent Series Resistance (ESR) - Compared to batteries, they have a low internal resistance. Thus, providing high power density capability.

• Fast charge/discharge – they can be charged and discharged without damaging to the parts.

Applications • High Voltage Electrolytic used in power supplies.

• High Voltage disk ceramic; small size and capacitance value, excellent tolerance characteristics.

• CMOS RAM, IC for clocks• High current supply for a

short• Micro computer, RAM• Power source of toys, LED,

buzzer• Driving motor

Advantages

• Long life: It works for large number of cycle without wear and aging.

• Rapid charging: it takes a second to charge completely(due to their low internal resistance)

• Low cost: it is less expensive as compared to electrochemical battery.

• High power storage: It stores huge amount of energy in a small volume(The supercapacitor consists of large surface area electrodes and very thin dielectric)• Faster release:Release the energy much faster than battery

Disadvantages

Has the highest dielectric absorption of any type of capacitor.

High self-discharge - the rate is considerably higher than that of an

electrochemical battery.

Cells hold low voltages - serial connections are needed to obtain

higher voltages. Voltage balancing is required if more than three

capacitors are connected in series.

Due to rapid and large release of energy (albeit over short times),

EDLC's have the potential to be deadly to humans.

Applications Some of the earliest uses were motor start-up capacitors for large

engines in tanks and submarines China is experimenting with a new form of electric bus (capabus)

that runs without powerlines using large on-board EDLCs Germany has operated a light-rail vehicle (LRV) that uses EDLCs to

store braking energy. EDLCs can be used in PC Cards, flash photography devices in

digital cameras, flashlights, portable media players, and in automated meter reading, particularly where extremely fast charging is desirable.

Used as backup energy source for GPS guided missiles

CONCLUSION

Supercapacitors may be used where high power or energy storage is required.

Supercapacitors can be used widely because of their long life & short charging time.

On the other hand it has limitations due to its high cost, self discharge, packaging problems etc.