Basic electricity / The Capacitor

Greetings once again dear readers, continuing with the learning about electricity and electronics, today I want to share with you knowledge about capacitors. Before we start I want to say that at first the explanations and studies on electronic components seem to make little sense because these elements by themselves have very few functions, but when we analyze circuits of electronic applications we will find these elements, then we will know that these previous studies will have been worthwhile. When we analyze circuits we will find passive and active components. I already described the passive component of greater use that is the resistance, now it is the turn of another passive component, the capacitor. For this article I intend to define its technology, operation and some applications in which they are used, if you have any questions after reading please do not stay with it, use the comments section and I will gladly answer your questions.

The physical shape of the different capacitor. Pixabay

A capacitor is a component that has the ability to store electrical charges and supply them at the right time for a very short period of time. What it does is that it accumulates energy in the form of an electric field while it is charged, this energy can be retained in the element even when the main power source of the circuit is disconnected, its charge and discharge times depend on the capacitor capacity and the resistance through which it receives the charge, remember in previous publications that the resistance limits the passage of current so that I=V/R (Ohm's Law).

The capacity of the element is the property of storing electrical charges when subjected to a voltage and is given by the formula C=Q/V Where
C: Capacity in Faradian (F)
Q: Load stored in Columbus
V: Electrical voltage
The capacitors have small capacities with respect to their basic magnitude, being the largest of them in millifarads (mF)=0.001F or 10E-3F, up to picofarads (pF)=0.0000000000000001F or 10E-12F.

To determine the energy stored in a capacitor, it is sufficient to take into account its capacity and the voltage at which it is supplied. For which we can use the formula E=C x V²/2

Internally they are formed by two metallic plates (reinforcements) facing each other and separated by a polarizable insulator (dielectric), such as air, paper, ceramic, mica, plastics, among others, the dielectric is a fundamental component in the creation of these components since it influences the capacity and the temperature coefficient.

Capacitor structure commons.wikimedia

A dielectric is a non-conductive material (already described in previous articles) which means that it does not allow the charges that reach the capacitor to pass through it; but when the capacitor is charged, an electric field is generated by the storage of charges in its plates, this causes the dielectric, since its molecules are polarized, to be oriented in the form of dipoles so that the negative pole is attracted by the positively charged plate and vice versa. In ideal conditions we can say that the plate plates are filled with positive and negative charges respectively, until reaching the same potential of the source. If the voltage of the source drops, the capacitor gives up its loads until the voltage is equalised, thus making the field external and internal electrical power are matched.

These components as well as others are affected by the temperature which makes their capacities decrease, the effect of the temperature will depend on the composition of the dielectric as I mentioned above, I have taken the dedication to make a table for you, (I want my items to be well presentable)

Dielectric material	Temperature coefficient (both per thousand ºC)
Mica	+0.1
Paper	+0.5
Plastic	-0.15
Polyester film	+0.3
Metallised polyester	+0.3
Polycarbonatemetalized	+0.3
Electrolytic of foil	+1 or +5
Tantalum electrolytic	+1

Capacitors cannot be subjected to any voltage level, the maximum values must be known to avoid destroying the component, capacitors can generally be subjected to three types of voltages:

• Test voltage, usually double or triple the voltage at which the capacitor will normally work (without exceeding the maximum voltage indicated by the manufacturer), is used to check the characteristics of the insulators.

• Working voltage, is the maximum voltage at which the capacitor can be permanently operated without deteriorating.

• Peak voltage, is the maximum voltage that can be operated for short intervals of time, usually in minutes per hour of operation.

I have decided to create a table to share with you the voltages of the capacitors based on the type of capacitor, even so, I recommend always to verify with the manufacturer's instructions.

Type of capacitorl	Values	Maximum working voltage	Tolerances
Mica	2 pF to 22 nF	250 to 4000 V	0,5 to 20 %
Paper	1 nF to 10 uF	250 to 1000 V	5 - 10 - 20 %
Polystyrene	10 pF to 4,7 nF 4,7 pF to 22 nF	25 to 63 V 160 to 630 V	+/- 1pH (<50pF) 2,5 - 5 - 10 %
Polyester	4,7 nF to 1,5 uF 1 nF to 470 nF	100 to 160 V 400 to 1000 V	5 - 10 - 20 %
Metallised polyester	47 nF to 10 uF, 10 nF to 2,2 uF, 10 nF to 470 nF	63 to 100 V, 250 to 400 V, 630 to 1000 V	5 - 10 - 20 %
Polycarbonate metalized	47 nF to 10 uF, 10 nF to 2,2 uF, 10 nF to 470 nF	63 to 100 V, 250 to 400 V, 630 to 1000 V	5 - 10 - 20 %
Ceramic (I)	0,56 pF to 560pF, 0,47 pF to 330 pF	63 to 100 V, 250 to 500V	2 - 5 - 10 %
Ceramic (II)	4,7 nF to 470 nF, 220 pF to 22 nF, 100 pF to 10 nF, 470 pF to 10 nF	15 to 50 V, 63 to 100 V, 250 to 500 V, 1.000 V	(-20 + 50 %), (-20 + 80 %), +/- 20 %, (-20 + 50 %)
Aluminium electrolytic	100 to 10.000 uF, 2,2 to 4.700 uF, 0,47 to 2.200 uF, 2,2 to 220 uF	4 to 10 V, 16 to 40 V, 63 to 160 V, 200 to 450 V	(-10 +50 %), (-10 +100 %), (-20 + 30 %), (-10 + 50 %)
Tantalum electrolytic	2,2 to 100 uF, 220 nF to 22uF	3 to 10 V, 16 to 40 V	+/- 20 %, (-20 + 50 %)

As I said before, the charge and discharge of a capacitor will depend on the capacitor capacity, the resistance used for this purpose and the voltage applied. In ideal conditions the capacitor will always try to charge at the same value of the voltage source, for a practical demonstration I will use the livewire simulator, in it I will simulate the charge and discharge so we can see it graphically.

Circuit to illustrate the charging and discharging of a capacitor, with the support of the virtual oscilloscope to visualize the corresponding graph. Image created by the author using the livewire simulator

We can see in the circuit that the circuit breaker is positioned to energize the capacitor, I have chosen a high value for the resistance in order to increase the charging time, this way we will have a better appreciation. With the support of the virtual oscilloscope provided by the simulator, we can visualize the load graph.

Voltage/time graph to illustrate the charging of a capacitor. Image created by the author using the livewire simulator

When the voltage in the capacitor reaches the value of the battery voltage, they remain at the same potential, and current stops flowing. One thing we can notice immediately is that the load curve is exponential. If we want to calculate the value of the load stored by the capacitor in an instant we can apply the formula Q = CV(1-e^-t/RC). In real conditions, the capacitor is never fully charged due to the existing pressure drop. Theoretically, we can consider that it has been charged when a time (t) has elapsed, which is determined by the following formula t = 5RC, note that the R and C variables are the ones that can manipulate this time, in the future we will use this to create timers.

We can consider the charging time equal to the discharge time, if we change the positioner switch we can notice the discharge graph of the capacitor.

Voltage/time graph to illustrate the discharging of a capacitor. Image created by the author using the livewire simulator

Its use in electrical and electronic circuits is very varied, for example: current filtering, oscillator circuits, timers, transmitter tuners, electronic ignitions, avoiding the passage of direct current from one circuit to another, phase emulator for single-phase motors among many others.

An important thing to note is that the capacitor behaves like an open circuit when direct current is applied to it, and if it is alternating it acts as a closed circuit creating an impedance related to the frequency of that current, which allows the passage of current in one direction only, this property is used for filtering alternating current.

Other recommended readings

1. Basic electricity / introduction

2. Basic electricity / DEFINITION OF ELECTRICITY

3. Basic electricity / Electicity Generators

4. Basic electricity / ELECTRICAL CONDUCTOR AND RESISTANCE

5. Basic electricity / Resistances, load and Ohm Law

6. Basic electricity / Resistive circuits

7. Mulukutla S. Sarma. Introduction to Electrical Engineering
   New York Oxford
   OXFORD UNIVERSITY PRESS
   2001

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I hope you found this publication useful. My intention is that we can know the essential components and then create circuits that can be useful to us. Thank you once again for reading, I bid you farewell wishing God to give you wisdom and bless all your projects according to his will for your well-being.