Somehow, the capacitor is a kind of battery. Although they work in totally different ways, capacitors and batteries also store electricity. Inside the batteries, a series of chemical reactions produce electrons on one terminal and "absorb" them from the other. A capacitor is simpler than a battery, in the sense that it does not produce electrons, but only stores them.
So the capacitor is a passive electrical device that stores energy in the form of an electric field between two fittings charged with an equal electrical charge, but of opposite sign. It is also known as the capacitor. The unit of measurement, in the international system, for the electric capacity is the farad (noted F). The capacitors can be of several types (electrolytic, tantalum, etc.), being made both in surface mounted device (SMD) and THD (trough hole device) technology.
Inside the capacitor, the terminals are connected to two metal plates separated by a dielectric (non-conductive) material. You can easily make a condenser with two pieces of aluminum foil separated by a piece of paper.
It will not be a very good capacitor in terms of its capacity to accumulate electricity, but it will work.
In theory, any non-conductive material can be dielectric. However, for practical applications, specific materials are used to obtain the best results. Mica, ceramics, cellulose, porcelain, Mylar, Teflon and even air are some of the dielectric materials used in capacitors. The dielectric used dictates the type of capacitor and what it is used for. Depending on the size and type of the dielectric, some capacitors are better for high frequency electric currents, while others for high voltages. Capacitors can be used for almost any purpose, from small capacitors on your computer to huge capacitors that power a bus. NASA uses glass-dielectric capacitors to turn on the huge electrical systems of shuttles and space stations.
Here are some of the dielectrics used in capacitors and what capacities they give them:
- Air - often used in radio circuits;
- Mylar - often used for clock circuits, stopwatches and other time measuring devices;
- Glass - good for high voltage applications;
- Ceramic capacitors - used for high frequencies, in devices such as antennas, X-ray or MRI scanners;
- Super capacitors - used on electric and hybrid machines.
1. The capacitor circuit
In a schematic representation of an electrical circuit, a capacitor is thus presented, depending on its type.
When you connect a capacitor to a battery, here's what happens (see fig. Below):
- The plate of the capacitor that is attached to the negative terminal of the battery accepts the electrons produced by it;
- The plate of the capacitor that is attached to the positive terminal of the battery loses electrons, which go to the battery.
Once charged, the capacitor will have the same electrical voltage as the battery (if the battery has 1.5 volts, then the capacitor will also have 1.5 volts). For a small capacitor, the capacity is small. Large capacitors can withstand a little more electrical charge. You can find capacitors as much as a can that can support enough electrical charge to make it possible to light a bulb for a minute or more.
Even nature has a "capacitor" that works in the form of lightning. One "plate" is the clouds, and the other is represented by the earth, and the lightning appears between these two "plates". Obviously, with a capacitor of this size, enough load can be stored to produce lightning.
Pictured above is a circuit consisting of a bulb, a battery and a capacitor. If the capacitor is large enough, you will notice that when you connect the battery, the bulb will illuminate as the battery current flows to the capacitor and this accumulates electrical charge. The light of the bulb will increase in intensity until the capacitor reaches its maximum capacity. If you disconnect the battery from the circuit and replace it with a wire, the current will flow from one capacitor board to the other. The bulb will initially emit an intense light which then decreases in intensity as the capacitor discharges.
The capacity of electrical charge storage by the capacitor, or capacitance, is measured in the International System in units called pharyngeal units. A capacitor of a farad can store a charge coulomb at one volt. A coulomb has 625 X 1016 electrons. An ampere represents a rate of electrons of 1 coulomb per second, so a capacitor of a farad can sustain one ampere per second at a voltage of one volt.
A capacitor of a farad is quite large. For this reason, capacitors are usually measured in farult submultiples, in units such as microrodar (mF) and picofarad (pF).
To get a sense of how big a farad is, think about it:
- A standard alkaline AA battery has about 2.8 amps / hour;
- This means that a standard alkaline AA battery can produce an electric current of 2.8 amps and a voltage of 1.5 volts for one hour (about 4.2 watts per hour such a battery can keep a light on 4 watts approximately one hour);
- Let's say the battery produces current with a voltage of one volt to simplify calculations. To store the energy of an AA battery with a current intensity of 2.8 amps and a voltage of one volt in a capacitor, you should have a capacitor of 3600 X 2.8 = 10080 headlights, because one ampere per hour equals 3600 amps. per second.
3. Energy stored
As opposite charges that accumulate on the plates of a capacitor due to a separation of the loads, a voltage develops in the capacitor due to the electric field of these loads. The increase of the energy is done against the electric field, being separated more electrical charge. The energy (measured in SI in joules) stored in the capacitor is equal to the action required to determine the voltage in the capacitor and, implicitly, the electric field. The stored energy is calculated by the formula:
where "V" is the voltage (electrical voltage) at the capacitor terminals.
The maximum energy that can be stored (safely) in a capacitor is limited by the maximum electric field that the dielectric material can withstand before breaking down. Therefore, all capacitors using the same dielectric material have the same energy density (joules per cubic meter).
The difference between a capacitor and a battery is that a capacitor can discharge all the electrical energy in a fraction of a second, while a battery needs minutes to fully discharge. This is why the electronic flash of a camera uses a capacitor - the battery charges the capacitor for a few seconds, and it releases all the charge it has accumulated in the flash lamp almost instantly. This makes large capacitors extremely dangerous - TVs and other devices containing large capacitors have warnings about opening them.
Capacitors are used in electrical circuits in several different ways:
- Sometimes they are used to store energy and use it at high speeds. This makes lightning. Large lasers use this technique to generate bright, instantaneous spark.
- Condensers can also remove pulses. If a DC power path "has pulses", a capacitor can absorb "peaks" and fill "valves", so smooth the (voltage) waveform.
- A capacitor can block DC voltage. If you connect a capacitor to a battery, when fully charged, the current will no longer flow between the poles of the battery. However, any alternate signal passes through an unsteady capacitor. This is because the capacitor is charged and discharged with the fluctuations of the current, making it appear that it passes through it.
5. History of the capacitor The
invention of the capacitor varies somewhat depending on who you ask. There are documents that indicate that German researcher Ewald Gorg von Kleist invented the condenser in November 1754. Several months later, Pieter van Musschenbroek, a Dutch professor at Leyden University came up with a similar device, called the Leyda bottle, which is considered the first capacitor. Because Kleist did not have very detailed journals and notes, he was often regarded as a contributor to condenser development, not his inventor. However, over the years, it was established that their research was independent and that it was just a coincidence between them.
Leyda bottle is a very simple device. It consists of a glass jar, half filled with water, and lined inside and outside with metal foil. The glass acts as a dielectric, although water has long been believed to be the key ingredient. There is usually a metal wire or chain that is passed through a cork stopper (or other insulating material). The chain is bent on something that will distribute the load. Once the current is transmitted into the cylinder, it should be able to withstand two opposing but equal charges until it is connected to a wire, producing a spark or shock.
Benjamin Franklin used the Leyda bottle in his experiments with electricity and found that a piece of flat glass works just like the Leyda bottle, thus developing the flat capacitor or Franklin square. Several years later, the English chemist Michael Faraday used capacitors in the first practical applications in trying to store unused electrons from his experiments. This was the first usable capacitor, made of large oil barrels. Faraday's progress on capacitors is what allowed us to "transport" electricity over long distances. As a result of Faraday's accomplishments in the field of electric fields, the unit of measure of capacitor capacity is the farad.
6. Electrical circuits
6.1 DC sources
The dielectric material between the plates is an insulator that stops the flow of electrons. A constant electrical current flowing through a capacitor "stores" electrons on one plate and takes the same amount of electrons from the other plate. This process is called "loading". The current passing through the capacitor results in the charge separation from within it, which develops an electric field between the plates of a capacitor, developing a voltage difference between plates equivalent to the electric current passing through it. This voltage (V) is directly proportional to the amount of separate load (Q). Since current (I) in the capacitor is the rate at which the charge (Q) is "forced" through the capacitor (dQ / dt), it can be mathematically expressed:
where "I" is the current flow in the conventional direction, measured in amperes, "dV / dt" is the voltage derived time, measured in volts per second, and "C" is the capacitance measured in farars.
For circuits with a constant (continuous) voltage source and consisting only of resistors and capacitors, the voltage passing through the capacitor may not exceed the voltage at the source. Thus, a balance is reached where the voltage passing through the capacitor is constant and the current from the capacitor is zero. For this reason, capacitors are said to block DC.
6.2 Alternative power sources
The right current for a capacitor is the alternating current, which changes its direction periodically. This type of electrical current is best suited for a capacitor because it charges the plates alternately: in one direction it charges one plate and when it switches it charges it on the other. Except when the electric current changes direction, the capacitor current is different from zero throughout a cycle. For this reason we can say that the capacitors let the alternating current "pass". However, electrons never pass directly from one plate to another unless the dielectric material is broken. Such a situation leads to physical damage to the capacitor and sometimes to the electrical circuit in which it is located.
Because the voltage passing through the capacitor is proportional to the integral of the electric current, with the sine of the waves in the alternating current or the signal of the circuits, in this phase an angle of 90 degrees results, the current driving the voltage of the transit angle. It can be shown that the voltage of the alternating current passing through a capacitor is in the quadrant with the alternation of the current through the capacitor. This means that the voltage and the electric current are offset by a quarter of a cycle. The amplitude of the voltage depends on the amplitude of the current divided by the product of the frequency of the current with the capacitance.
The phase voltage rate ("phase" is a complex number, which represents the amplitude of a sinusoidal function of time) that traverses an element of the circuit towards the phase current. That element is called the impedance (Z). Impedance describes a measure of the opposition of an AC current. For a capacitor, this is calculated by the formula:
is the capacitive reactance,
ω = 2πf is the angular frequency ("f" is the frequency, "C" is the capacitance measured in farars, and "j" is the "imaginary unit").
From here, the capacitive reactance is the imagined negative component of the impedance. The negative sign indicates that the electric current brings the voltage to 90 for the sine signal, as opposed to the inductor,
The impedance is similar to the resistance resisted by a resistor. The impedance of a capacitor is inversely proportional to the frequency, so for alternating currents with very high frequencies, the reactance is close to zero - so a capacitor is close to a short-circuit to alternating currents with high frequency.
In contrast, for low-frequency alternating current, the reactance grows outside the capacitor, so this is an open circuit for a low-frequency alternating current. This behaviorally dependent frequency describes most capacitor functions.
The reactor is so called because the capacitor does not waste energy, but stores it. In electrical circuits, as in mechanics, there are two types of loads: resistive and reactive. The resistive loads (they resemble by analogy with an object that moves on a rough surface) dissipate the energy from the circuit in the form of heat, and the reactive loads (they resemble by analogy with an object that moves on a surface where the friction is very small ) stores the energy, introducing it back into the circuit.
Also significant is the impedance which is inversely proportional to the capacitance, as opposed to inductors and resistors, where the impedance is proportional to the resistance and the inductance, respectively. So the impedance formula for serial and parallel bonding is the inverse of the resistive case; in series, the sum of the impedances, and in parallel the sum of the conductance (conductivity).
6.4 Serial or parallel connection
Capacitors in a parallel configuration have the same potential difference (voltage). Their total capacitance (Ceq) is given by the formula:
The reason for connecting capacitors in parallel is to increase the total stored energy. In other words, increasing the capacity increases and the energy that can be stored. The formula by which this can be calculated is
The electrical current passing through the capacitors connected in series remains the same, but the voltage passing through each capacitor may be different. The sum of the potential differences (voltages) is equal to the total voltage. Their total capacitance is given by the formula:
In parallel, the effective surface of the combined capacitor has increased, increasing the total capacitance, while, in series, the distance between the plates is effectively reduced, thus reducing the total capacitance.
Basically, connecting the capacitors in series means economically obtaining high-voltage capacitors, which can be used, for example, to stabilize the electrical current coming from a high-voltage source. Three 600-volt capacitors connected in series will "create" an 1800-volt capacitor. This is of course the capacitance obtained from the connection of capacitors in series, each having a third of the total capacitance. Opposite these results, it is possible to obtain, by connecting the same capacitors in parallel, we obtain a 3X3 capacitor array, with the same total capacitance with a single capacitor, but operable at three times lower voltages. In this application, a resistor will be connected "in front"
Another application of this arrangement is the use of polarized capacitors in alternating circuits; the capacitors are connected in series, with reverse polarity, so at any time, a capacitor will be non-encoder.
7. Types of capacitors
[Ordered by dielectric material:]
a). Vacuum: two electrodes, usually of copper, are separated by a vacuum. The insulating coating is usually made of glass or ceramic material. They typically have small capacities between 10 and 1000 peaks and voltages over 10 kilowatts (kV) are often used on radio transmitters and other devices that use high-voltage electrical currents. This type of capacitors can be fixed or variable. Variable vacuum capacitors can have a minimum to maximum capacitance ratio of over 100, allowing any starting circuit to cover a full decade of frequencies. The vacuum closest to perfection between the dielectrics with the tangential loss equal to zero. This allows the transmission of electricity without significant loss and heat release.
b). The air: a capacitor which has air dielectric material, consists of two metal plates, usually made of aluminum or silver plated brass. Almost all air capacitors are variable and are used in radio wave circuits.
c). Metallic plastic foil: these capacitors are made from a high quality polymer foil (usually polycarbonate, polystyrene, polypropylene, polyester, and for high quality capacitors, polysulfone), and a metal foil or layer that covers this plastic foil. They have good quality and stability and are suitable for timer circuits. Suitable for high frequencies.
d). Small: Similar to those of metal foil. Often for high voltage. Suitable for high frequencies. Expensive.
e). Paper: Use for relatively high voltages. Now outdated.
f). Glass: Use for high voltage. Expensive. Stable temperature coefficient over a wide range.
g). Ceramics: Thin, alternative, metal and ceramic layers. The temperature and capacitance depend on the ceramic material used as a dielectric, and whether they are in class I or II. They have (especially those in the second class) a high dissipation factor, a high frequency dissipation coefficient, their capacity depends on the voltage crossing them, their capacity changes with age. However, they are used in many low-precision coupling and filtering applications. Suitable for high frequencies.
h). Electrolytic aluminum: Polarized. Similar in structure to those with metal foil, but the electrodes (plates) are made of pickled aluminum plates to gain a larger surface. The dielectric is made of a material soaked in a substance called electrolyte. They may have large capacities, but suffer from low tolerances, high instability, gradual loss of capacity especially when subjected to heat and electrolyte leakage. They tend to lose their capacity at low temperatures. Not suitable for high frequency currents.
i). Electrolytic tantalum: similar to aluminum-electrolytic capacitors but with better temperature and frequency characteristics. High dielectric absorption. High leakage. They have higher performances at low temperatures.
j). OS-CON: Capacitors made from a solid-electrolyte polymerized organic semiconductor that offer a longer lifetime and a higher cost.
k). Supercapacitors: Manufacture from carbon aerogels, carbon nanotubes or high porosity electrodes. Extremely high capacity.
it). Epic capacitors ": They are made of two insulated conductors that have been twisted. Each conductor behaves like an electrode of the capacitor. Epic capacitors" are a form of variable capacitors. Small changes in capacitance (20% or less) are obtained by twisting and loosening the two conductors.
m). Varactor or varicap: There are special capacitors with reverse diode thresholds whose capacitance decayed with the voltage. Use inter alia in loops locked in phase.