Super Capacitor

SuperCapacitors are electrical energy storage devices capable of storing large amounts of electrical charge.

Unlike resistance, which emits energy in the form of heat, the ideal capacitor does not lose its energy.We found that the simplest form of a capacitor is two parallel conductive metal plates, separated by an insulating material such as air, mica, paper, ceramics, etc., and called dielectric, which pass through the "d" distance.

Depending on the voltage, as a result of the amount of charge collected for a capacitor and their ability to charge the tank, capacitors are applied throughout the energy tank, V, plates, and a larger voltage is recorded by the capacitor as a greater load: Q, ∞ V.

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Super Capacitor

In addition, a capacitor has a proportional constant called capacitance, which represents the capacity or capacity to store an electrical charge with the amount of load depending on the capacitor capacitance value: Q ∞ C.

Then we can see that there is a relationship between load, Q , voltage V and capacitance C, and the larger the capacitance, the higher the amount of load stored in a capacitor for the same voltage, and we can define this relationship:

Charging in capacitor

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Where: Q (Charge, in Coulomb) = C (capacitance, in Persian) times V (Voltage, volts)

The capacitance unit is Coulomb/volt and is also called Farad ( F ) [M. After Faraday] and a farce is defined as the capacitance of a capacitor, which requires a load of 1 coulomb to make a potential difference.

But a conventional farad capacitor will be too large for most practical electronic applications, so much smaller units such as microfarad ( μF ), nanofarad ( nF ) and picofarad ( pF ) are widely used in the following cases:

  • Micropharmaceutical (μF) 1μF = 1/1,000,000 = 0.00001 = 10 -6 F
  • Nanofarad (nF) 1nF = 1/1,000,000,000 = 0.000000001 = 10 -9 F
  • picofarad (pf) 1pf = 1/1,000,000,000,000 = 0.00000000001 = 10 -12 F

However, there is another type of capacitor called Ultracapacitator or Super capacitor, which can provide capacitance values from several shafts-farads (mF) to ten headlights and allow much more electrical energy to be stored between them.

In our tutorial on Capacitance and Charging, we found that the energy stored in a capacitor is given by equation:

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Where: E is the energy stored in joule in the electric field, V is the potential difference between the plates, and C is the capacitor's capacitance in farce and is defined as follows:

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Where: ε is the permeability of the material between the plates, A is the area of the plates, and d is the separation of plates.

A supercapacitor is another type of capacitor made to have a large conductive plate called an electrode, surface area (A) and a very small distance (d) between them.Unlike traditional capacitors that use a solid and dry dielectric material such as Teflon, Polyethylene, Paper, etc., the supercapacitor uses liquid or wet electrolytes between its electrodes, making it an electrochemical device similar to an electrolytic capacitor.

AAlthough the supercapacitor is a type of electrochemical device, there is no chemical reaction in the storage of electrical energy.This is ultra-means that the supercapacitor remains actively as an electrostatic device that stores electrical energy in the form of an electric field between two conductive electrodes, as shown.

Super Capacitor Structure

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Double-sided coated electrodes are made of graphite carbon in the form of active conductive carbon, carbon nanotubes or carbon gels.A porous paper membrane called a separator keeps electrodes separate, but allows positive ion to pass through while blocking larger electrons.Both paper separator and carbon electrodes are impregnated with liquid electrolytes with an aluminum foil used between the two to act as current collectors that electrically connect ultracapacetors to soldering nails.

The double-layer structure of carbon electrodes and separators can be very thin, but their effective surface area reaches thousands of square meters when wrapped together.Then, in order to increase the capacitance of a supercapacitor, it is clear that we need to increase the contact surface area, A (in m 2) or use a special electrolyte to increase the available capacity, without increasing the physical size of the capacitors.

However, the problem with this small size is that the voltage on the capacitor can be very low, since the rated voltage of the ultra-capacitor cell is mainly determined by the degradation voltage of the electrolytin.A typical capacitor cell then has a working voltage of 1 to 3 volts, depending on the electrolyte used, which can limit the amount of electrical energy it can store.

Ultracapacetors need to be serially connected to store the charge at a reasonable voltage.Unlike electrolytic and electrostatic capacitors, ultracapacitors are characterized by low terminal voltage.There, ultracapacitor cells must be connected serially or in parallel to achieve higher capacitance values, as shown, in order to increase the rated terminal voltage to dozens of volts.

Increasing the Value of an Ultracapacitor

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Where: VCELL is the voltage of a cell, and CCELL is the capacitor of a cell.

Since the voltage of each capacitor cell is about 3.0 volts, serially connecting more capacitor cells will increase the voltage.It will increase capacitance when connecting more capacitor cells in parallel.Then we can define the total voltage and total capacitance of an ultracapacitator bank as follows:

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Where: M is the number of columns and N is the number of rows.Note that, like batteries, ultracapacitors and supercapacitors have a polarity defined by a positive terminal marked on the capacitor body.

Super Capacitor Question Example 1

An electronic circuit requires a 5.5 volt, 1.5 farad supercapacitor as an energy storage backup device.If the supercapacitor will be made individually from 2.75v, 0.5F cells, calculate the required number of cells and the layout of the array.

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Therefore, the array will have two capacitor cells of 2.75v, each serially connected, to provide the required 5.5v.

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The array will then have a total of six separate columns consisting of two rows of six, thereby creating an ultracapacitor with a sequence of 6 x 2, as shown.

6×2 Ultracapacitor Array

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Ultracapacitor Energy

Like all capacitors, an ultracapacitator is an energy storage device.Electrical energy is stored as a load in the electric field between the plates, and as a result of this stored energy, a potential difference between the two plates, i.e. voltage, is formed.During charging (current passing through the ultracapacitor from the connected supply), electrical energy is stored between the plates.

When the ultracapacitor is charged, the current flow from the source stops, and the terminal voltage of the ultracapasitors is equal to the voltage of the source.As a result, a rechargeable ultracapacitator will store this electrical energy until it functions as an energy storage device, even when removed from the voltage source.

When ejaculating (the current flows out), the ultracapacitor converts this stored energy into electrical energy to feed the connected load.Then an ultracapacitator itself does not consume any energy, instead the amount of energy stored in the ultracapacitator stores and releases electrical energy in proportion to the capacitance value of the capacitor.

As already mentioned, the amount of energy stored is proportional to the square of the V voltage along the C capacitance and terminals.

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Where: E is the energy stored in joule.Then for our example of the above ultracapacitor, the amount of energy stored by the array is given as follows:

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Then the maximum amount of energy that can be stored by our ultracapacitor is 22.7 jul, which was initially provided by the 5.5 volt charging source.This stored energy remains available as a charge in electrolyte dielectric, and when connected to a charge, all 22.69 jul of ultracapacitor energy is supplied as an electric current.Obviously, when the ultracapacitor is completely discharged, the stored energy is zero.

Then an ideal ultracapacitor does not consume or distribute energy, instead it takes power from an external charging circuit to store energy in the electrolyte field, and then gives back this stored energy while powering a load.

In our simple example above, the energy stored by the ultracapacitor was about 23 joules, but with large capacitance values and higher voltage ratios, the energy density of ultracapacitors can be very large, making them ideal as energy storage devices.

In fact, ultracapacetors with thousands of farads and ratings of up to hundreds of volts are now used as solid-state energy storage devices for regenerative braking systems in hybrid electric vehicles (including Formula 1), since they can quickly energize and receive during braking.Ultra and supercapacitors are also used in renewable energy systems to replace lead acid batteries.

Summarize

A supercapacitor is an electrochemical device consisting of two porous electrodes consisting of activated carbon, usually immersed in an electrolyte solution that stores the load electrostatically.This arrangement effectively creates two capacitors, one in each serially connected carbon electrode.

The ultracapacitor is available with hundreds of farce capacitances, all of which are of a very small physical size, and can achieve much higher power density than batteries.However, the voltage rating of an ultracapacitor is usually less than about 3 volts, so several capacitors need to be connected in series and parallel combinations to provide any useful voltage.

Ultracapacetors can be used as battery-like energy storage devices and are actually classified as an ultracapacitor battery.But unlike a battery, ultracapasitors can reach much higher power densities in less time.In addition, ultracapacitors are now used in many hybrid gasoline vehicles and fuel cell electric vehicles, due to their ability to discharge high voltages quickly and then recharge once again for the next cycle.Using ultracapasitors along with conventional fuel cells and automotive batteries, the highest power demands and temporary changes in load conditions can be controlled much more effectively.