ELECTRONICS REPAIR COURSE NOTES.

CAPACITORS.

BY
NYERO VINCENT.

Technician and director NERS GULU.

(NYERO ELECTRONIC REPAIR SHOP GULU)

TELL. +256 775442110

NB. This book only contains the basics electronic knowledge on capacitors required for
repairing electronic/electrical devices.
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Introduction.
Electronics. Can be defined as;
1. Branch of science that deals with the study of flow and control of electrons and the study of their behaviors and effect
in Vacuum, gases, semiconductor and devices that uses such electrons.
2. Branch of physics and technology concerned with the design of circuit using electrical components/parts with the
behaviors and movement of electrons in semiconductors, conductors, vacuum etc.
ELECTRONIC DEVICES
Electronic devices are sometimes called electronics. Therefore, electronics can also be defined as device that operates
using many small electrical parts.
Examples of electronic devices.

Television (TV), phones, radios, computers/laptops, home theatres/woofers, cameras, projectors etc.

SOME OF THE COMMON TERMS, ABBREVIATIONS AND CIRCUIT SYMBOLS USED IN ELECTRONICS
(GLOSSARY).

Terms used.

Technician. Is a person who helps designs, test, manufactured, install and repair electricals and electronic equipment
such as communication equipment, medical monitoring devices, computers etc.

Multimeter. Is a measuring instrument that can measure multiple electrical properties. A typical multimeter can
measure voltage, current and resistance etc.

Electricity. Is the flow of electric chargers (electrons) within conducting matter in a complete circuit.

Electric current. Is a flow of electric charge.

Current. Is the rate of flow of electric charge, Current is represented by I and measured in Ampere.

Voltage. Voltage also known as potential difference (pd), electromotive force (emf), electric pressure or electric tension
is defined as the electric potential difference per unit charge between two points in an electric-fields. Voltage is
measured in volt (V).

Ampere. Is a unit of measure of rate of flow of electron/electric current in an electrical conductor.

Ampere or amp is represented by letter ‘A’.

Electron (n). Is a negatively charge carrier.

Holes (p). hole is a positively charged carriers.

Anode. Positive charged electrode.

Cathode. Negative charged electrode.

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Circuit. Circuit refers to interconnection of components to provide an electrical path between two or more components.

Electrode. Is an electrical conductor used to make contact with a non-Metallic part of a circuit.

Conductor. Material that allow the passage of electricity through it.eg. Copper, iron, aluminum, gold etc.

Insulator. Material that do not allow the passage of electricity through it.

Semiconductor. Material that partially allow the passage of electricity and partially do not allow the passage of
electricity through it.ie. Its property of conductivity lies between that of a good conductor and an insulator.eg. Silicon,
germanium etc.

Voltage source. Any device that provide us with voltage.eg batteries, electric generator and wall socket. Etc. or it is a
device that convert some other form of energy.eg chemical energy, mechanical energy etc. into electrical energy.

Resistance. Is the opposition of a conducting materials to the flow of electric current. It is measured in ohm (Ω). Or it
is the ability of a resistor to limit current flow.

Capacitance. Is the ability of a capacitor to store electric charge. It is measured in FARAD (F).

Inductance. Property of a component like a coil or an inductor to oppose any change in flow of current. It is measured
in Henry (H).

Power. Product of voltage (V) and current (I). It can also be defined as the time rate of doing work. It is measured in
WATT (W).

Work. Is power used during a period of time. It is measured in joules (J).

Open circuit. A circuit connection in which there is no flow of electric current.

Short circuit. Is a connection between two points in a circuit in the potential difference is zero (0V).

Series circuit. In series connection same current flow through each and every component.

Parallel circuit. In parallel connection, same voltage is applied across each and every component.

Through – hole devices. Electronic devices with long terminals that we put in the holes of PCB.

Surface mount devices (SMD). Devices that pins/legs are soldered on the surface of the PCB without any terminal
going into the holes.

Amplifier. Is an electronic device /circuit that produces an enlarge version of a small signal fed into the circuit.

Amplitude. Magnitude or size of a signal voltage or current.

Solder. Metallic alloy used to join two or more metal surfaces.

Soldering. To put legs of components on appoint on PCB.

De-soldering. To remove legs of components from a point in PCB.

Dismantle/disassemble. To put apart parts of electrical devices.

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Assemble. To fix or put back parts of electrical devices.

Loop/jumper. To connect one point to another in a circuit board.eg broken path, open circuit etc.
Direct current (DC). Unidirectional current.ie type of current that do not changes direction (flow in only one direction.eg.
batteries.
Alternating current (AC). Current which reverses direction/changes direction at regular intervals.eg. AC voltage
sources or alternators.
Impedance. Total opposition to the flow of current offered by a circuit.
Bias. A DC voltage applied to a device to control its operation.
Rectifier. Devices that converts AC into pulsating DC.
Cable. A group of two or more wires.
Polarity. Property of having a negative and positive charge/electrode.
Schematic diagram. Illustration of an electrical or electronic circuit with the components represented by their circuit
symbols and name prefixes/reference.
Troubleshooting. Procedures use for finding faults.
Terminals and connectors. Components to make electrical connection.
Network components. Components that use more than one type of passive component.
Transient voltage. A sudden high voltage spike in an alternating current system, caused by arcing or lightening.
Voltage breakdown. The voltage at which current suddenly passes in destructive amounts of dielectric.
Ripple. A small alternating current component in the output of a direct current power supply with inadequate filtering.
PWM. Pulse width modulation is a technique employed to regulate the output power by changing the pulse width. PWM
is employed in SMPS, UPS and many other power control applications.
Power surge. A momentary increase in the voltage on a utility line.
Impedance. Combination of resistance, inductance and capacitance which restricts the current through any device.
Attenuates. To reduce in amplitude.
wave form. Shape followed by any alternating current or voltage.
Bleeder resistor. A resistor or group of resistors used permanently to drain current from charged capacitors.
ESR. Equivalent series resistance.
Current limiting resistor. A series resistor inserted into circuit to limit the current to a desired value.

Abbreviations
Abbr. meaning
DC Direct current
AC Alternating current
TV Television
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F Fuses
S Switch
T Transformer
PCB Printed circuit board
B/Bat Battery
SP/SPK Speaker
CPU Central processing unit
CRT Cathode ray tube
MIC Microphone/mouth piece
GSM Global system for mobile
BSI Battery status indicator
LED Light emitting diode
IMEI International mobile equipment identity
UEM Universal power management
P.A Power amplifier
P.F.O Power frequency oscillator
VCO Voltage control oscillator
SMD Surface mount devices
VR Voltage regulator
RF Radio frequency
VBat Positive terminal of battery/connector
Gnd/GND Ground (negative terminal)
RT Thermistor
RAM Random access memory
ROM Read only memory
Rx Receiving section
Tx Transmitting section
PWR/P.Key Power key
REC Ear piece
A Ampere
AF Audio amplifier
BGA Ball grid array
DM/d- Data minus
DP/d+ Data positive
L Inductor
D Diode
C Capacitor
R Resistor
Q Transistor
Vbus/Vchg Bus voltage/Charging voltage
MOT Motor

Circuit Symbols
Below are some of the common circuit symbols used by manufacturers when designing circuit.
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Symbol meaning

Continuity/wire

Capacitor

Power diode/rectifier diode

Zener diode

Battery (DC voltage source)

Fuse

Switch

AC voltage source

Transformer

Coil/inductor

Resistor

variable resistor

Potentiometer
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LED

Transistor

DC voltage

AC voltage

AC current

DC current

ELECTRONIC COMPONENTS.

An electronic component is any basic discrete electronic device or physical part of an electronic system used to affect
electrons or their associated field.
Electronic components are categorized into two types;
1. passive components
2. Active components
PASSIVE COMPONENTS
Passive components are electronic components which can only receive energy which it can dissipate, absorb or store
it in an electric field or magnetic field.
Passive elements do not need any form of electrical power to operate.

Examples of passive electronic components.

Resistor, capacitor, inductor, transformer, thermistor, varistor (VDR), transducer etc.
ACTIVE COMPONENTS.
Active electronic components are components that supplies energy to a circuit.
Examples of active electronic components.
Transistor, generator, diodes (LED, photodiode, Zener diode, rectifier diodes), ICs, triacs, thyristor etc.
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NB. All semi-conductor devices falls under passive components.

OTHER ELECTRONIC/ELECTRICAL ELEMENTS

Fuse, switch, relays, crystal and resonator, cable/wire/conductor etc.
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CAPACITOR.

Basically, a capacitor is a device consisting of two metallic plates/conducting materials separated by an insulator
called dielectric or a capacitor is a device that opposes any change in voltage in a circuit.
A capacitor can also be defined as a device that stores electric charge (electrical energy) in an electric field.
The property by which a capacitor is able to store electric charge is called capacitance C or capacity.
The longer the plate area the more charge can be stored hence the larger the capacitance.

𝑸
The formula for capacitance C is. C = . where C is the capacitance, Q is charge in coulomb and V is the voltage in
𝑽
volt.
The SI unit of a capacitance is FARAD denoted by F.
Capacitor is usually represented by the capital letter C on circuit board.
Circuit symbols for capacitors.

Polarized capacitor Non-polarized capacitor.

USES OF CAPACITORS IN CIRCUITS.

Capacitors are used for hundreds of different purposes such as filtering, voltage regulating, by passing, power phase
correction, source of power, frequency controlling etc.
In order to understand uses of capacitors in the circuit, consider the characteristics of capacitors.
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A capacitor is simply a device and capacitance is an electrical property of a circuit which opposes changes in voltage.
The advantage of this property of capacitance makes it to be used in filter circuit (power supply circuit). This is why a
capacitor is placed every time we have a rectifier diode to smooth out the supply.

C1 is connected across the line voltage and the ground (GND).

A capacitor tends to store electrical charge and then release it as current in the circuit where it is connected, this is
also the reason why capacitor is connected after rectifier diodes to provide smooth DC (smooth out the supply).
Another x-tics of capacitors is that they allow AC to pass and blocks DC. Because of this x-tic, we can also use
capacitors in isolating or blocking DC voltage. To accomplish this, capacitor is usually placed in series with the signal.
A good example is found in audio circuits.
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In the diagram above, capacitor C1 is used in this circuit to allow the AC signal (audio) and blocking any DC from getting
to the speaker (SPK1). C2 is connected in line/series with the input signal (IN) from signal source usually MP3 or AUX.
If either C1 or C2 dries up then the device will have audio problems.

Another x-tic of capacitors is that they allow high frequencies to pass but makes it very hard for low frequencies to
pass. This is exactly the opposite of inductors. Using this x-tics of capacitors, a capacitor can be connected across the
power line. When the power line picks up unwanted radio frequencies, these frequencies which are very high will find
very little resistance when they get to a capacitor. Therefore, these unwanted radio frequencies will be shorted out to
the ground leaving the low supply frequency to proceed (50Hz or 60Hz). See an example here below of EMI FILTER
(Electromagnetic interference also called Radio frequency interference) found in all SMPS.

C1 and C2 are filter capacitors (polypropylene), L1 and L2 are inductors (choke coil)
NB: a filter element is a device used to pass desired signal and block undesired signal. To achieve this, we use some
known behavior of capacitors toward frequencies.
Capacitor allow high frequencies to pass but very hard for low frequencies to pass, since power supply has low
frequency of around 50Hz to 100Hz and radio frequencies are pretty high.
Looking at the circuit of the EMI above, the inductor here is in series with the supply line and therefore, will pass the
low supply frequency (50Hz) but make it hard for the high radio frequency to pass.
On the hand, the capacitor (C1) which is connected in parallel with the power supply (AC input line) effectively shorting
the high radio frequency to the ground hence allowing only the low supply frequency to pass.
NB: frequency. Is the number of occurrences of a repeating even per unit of time.
Radio frequency (RF). Is the rate of oscillation of an AC current, voltage or electromagnetic waves in an electronic
device or medium? These frequencies ranges from around 20KHz to around 300GHz.
EMI/RFI. Is unwanted electromagnetic energy polluting the environment. Its propagation via radiation and power
conduction over system signal and power lines can affect the operation of electrical equipment around the source. This
circuit consists of one or two coils (choke coil) and usually one or two non-polarity capacitors.eg polypropylene etc.
depending on the design. The function of this circuit is to attenuate leaking magnetic field to avoid RFI.
Attenuates. To reduce in amplitude.
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CAPACITOR BEHAVIORS.
Capacitor behavior in DC circuits.
When connected to a DC source, the capacitor charges and holds the charge as long as the DC voltage is applied.
The capacitor essentially blocks DC current from passing through.
NB: when the capacitor voltage equals the applied voltage, there is no more charging. The charge remains in the
capacitor with or without the applied voltage connected.

Capacitor behavior in AC circuits.

When AC voltage is applied, during the one half of the cycle, the capacitor accepts a charge in one direction.
During the next half of the cycle, the capacitor is discharged then recharged in the reverse direction. During the next
half cycle, the pattern reverses. It acts as if AC passes through the capacitor.
Although capacitors serve various functions on the circuit board, they are categorized into two mains groups.ie
1. Polarized capacitors.
2. Non- polarized capacitors.
Polarized capacitors.

Polarized capacitors are polarity sensitive capacitors.ie capacitors that has positive and negative terminals. Therefore,
should be inserted into the circuit board with positive terminal/legs to positive rail and negative leg to the negative
rail.eg electrolytic capacitors etc.
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Non-polarized capacitors.

These are not polarity sensitive and therefore, one can insert them on the circuit board either way. They are usually
rated less than 1µF.eg film capacitors, ceramic capacitors, variable capacitors etc.
NB: there are also another type of capacitor called bipolar which is marked NP on their body. These also are not polar.
They usually find their application on cross over circuit.

TYPES OF CAPACITORS.
Capacitors types vary in regards to the dielectric material used in their construction.
Below are some of the types of capacitors.
i) Film capacitor examples polyester, polystyrene, polypropylene, polycarbonate, metalized paper etc.
ii) Ceramic capacitor example ceramic disc capacitors
iii) Electrolytic capacitor example aluminum and tantalum.
iv) Variable capacitor example tuning caps, trimmers etc.
v) SMD capacitors (chip capacitors)

FILM CAPACITOR.
Film capacitors (plastic film capacitors) are non-polarized. Here an insulating plastic film acts as the dielectric.
Consist of relatively large family of capacitors with the difference being in their dielectric properties, this includes
polyester, Mylar, polystyrene, polypropylene, polycarbonate, metallized paper etc.
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Polyester (Mylar) polypropylene. Film polyester.

Film caps are available in capacitance range from as small as 5µF to as large as 100µF depending upon the actual
type of the capacitor and its voltage rating.

CERAMIC CAPACITORS.
Ceramic capacitors also known as disc capacitors are non-polarized capacitors made by coating two sides of a small
porcelain or ceramic disc with silver and then stacked together to made a capacitor.
Ceramic capacitors are mostly available in three different types.ie disc, tabular and button type but disc capacitors are
more economical to use than other types.

Disc ceramic capacitor. High voltage ceramic capacitors. SMD ceramic capacitor.
They normally vary in capacitance from 1pF up to about 1µF and have very high dielectric constant (k).
A code of three digits is generally printed on their body to tell their capacitance in Pico farad (pF). Where the first two
digits represent the value of the capacitor and the third digit represent the number of zeros to be added to the first two
values.eg 103pF=1000pF.
NB: sometimes letters are used for their tolerance.eg J=5%, K=10% and M=20% etc.

ELECTROLYTIC CAPACITORS.
Electrolytic capacitors are polarized capacitors. This means that correct polarity must be used when supplying DC
voltage to it.ie anode must be connected to the positive terminal and cathode to the negative terminal of the DC supply.
Not doing so (otherwise) will damage the capacitor.
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Radial aluminum electrolytic caps. SMD Tantalum electrolytic caps. Tantalum.

These types of capacitors are generally used where large capacitance is needed.

Electrolytic capacitors are grouped into the following three types.

i) Aluminum electrolytic capacitors.

Radial aluminum cap. Axial aluminum cap. SMD aluminum cap.

ii) Tantalum electrolytic capacitors.

Through-hole tantalum cap. SMD tantalum cap.

iii) Niobium electrolytic capacitors.
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NB: polarized and electrolytic capacitor won’t be connected to the AC supply as they are specially designed to be
operated only and only in DC circuits in the right way.
Electrolytic capacitors are widely used due to their low cost and small size but there are three easiest ways to destroy
them.
i) Over voltage.
ii) Reverse polarity.
iii) Over temperature.
(i). Over voltage.
When the capacitor maximum working voltage is exceeded, this over voltage will cause current to leak through the
dielectric resulting in a short circuit condition.
When designing circuit, the rule of the thumb is that the working voltage of filter capacitors should be double the
expected voltage in that line.eg when you find a capacitor on a source rated 25V then you can assume the voltage on
that line is around 12V (12 x 2 =24V).
NB; never use a capacitor into a circuit with higher voltage than the capacitor rated voltage. Otherwise it will become
hot and may explode/blast. Therefore, replace a capacitor with the same rating and size or voltage rating higher than
that of the capacitor to be replaced.
(ii). Reverse polarity.

Connecting capacitor such as electrolytic capacitors wrongly in circuit board will cause self-destruction of oxide layer
due to short circuit between the terminals via dielectric material. Hence, failure this can cause the capacitor to
explode/blast.
NB: tantalum capacitors may cause hazardous fire when wrongly connected or over voltage application.

(iii). Over temperature.

Excessive heat dries out the electrolytes and shortens the life of the capacitor. This will cause voltage fluctuation in the
circuit.ie capacitor won’t store enough energy hence producing a low output voltage (energy) to the circuit. In this case
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the device will have low power problem which may cause the device not to power ON (dead), blinking stand-by, auto
shut down (OFF), take long to turn ON etc.
NB: a dried-up capacitor causes failure in the line it is connected in (supplying energy to).eg when a capacitor is
connected across supply voltage line fails.eg dried up, swollen etc. there will be power fluctuation (low voltage).

VARIABLE CAPACITORS.
Variable capacitors are so designed that the capacitance value can be varied continuously within fixed limits. Variable
capacitors are often used in LC circuit to set the resonance frequency.eg to tune a radio. Therefore, it is sometimes
called tuning capacitor.
Symbol for variable capacitors.

The variable capacitors may use air as the dielectric as in the case of gang capacitors. Variable capacitors that uses
solid material as dielectric are known as trimmers and padders.

In the case of gang capacitors, capacitance is varied by varying the over lapping area between two sets of plates, one
set remains stationary and is called the stator, the set of plate can be rotated by means of a shaft and is called the
rotor. Whereas the stator is insulated from the frame, the rotor is generally connected directly to the shaft. Common
application is the tuning capacitors in radio receivers.
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The variable capacitor above (tuning capacitor) typically consists of four individually ganged capacitors, where two
gangs of variable capacitors are for the AM side and the other two gangs are for the FM side. Three pins on lower side
are usually for FM. Three pins on the upper side are usually for AM. Center pin is common to both sides.

In the diagram above C1 and C2 marks pins for FM circuitry, C3 and C4 marks pins for the AM circuitry.
The manufacturers usually provide two trimmers screws for each band. On FM side, there is a trimmer for the FM
antennae and the other for FM oscillator. Similarly, to the AM side.
The trimmers are useful if your radio had a dial and you are needed to calibrate the dial.
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NB: it is advisable to replace this tuning capacitor when they failed rather than tuning the trimmer screws. You can only
try to calibrate if in case someone tampered to turn the trimmer screws.
NB: adjustable capacitors that normally have slotted screw type adjustments are used for very fine adjustments in a
circuit are called trimmers.

SURFACE MOUNT CAPACITORS (SMD CAPACITORS).

SMD capacitors are capacitors that uses surface mount technology in their construction (design) and installation in
circuit boards.

SMD are preferred over through hole because of their small sizes. They are available both in polar and non-polar types.

CAPACITANCE UNIT.
The basic SI unit of capacitance is the FARAD which is used in all equation but this value is very large to be used in
electric circuit.
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In electronic circuit, smaller values are used such as Pico-farad, Nano-farad, microfarad etc.
Microfarad can be written as MFD, MF or µF or simply M. Nano-farad as nF, Pico-farad as pF.
The easiest way to understand capacitance value is to start with a value of 1µF and is one-millionth of a farad.

1µF=1/1000000 farad = 10-6.

1nF=1/1000000000 farad = 10-9.

1pF= 1/1000000000000 farad = 10-12.

Recapping.
1µF = 1000nF.
1nF = 1000pF.
NB: ceramic is marked in ‘’p’’ (puff). e.g. a ceramic marked with 22 is 22pF, 103 is 10000pF=10nF, 102 is
1000pF=1nF.

CAPACITANCE CONVERSION TABLE.

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UNDERSTANDING THE MARKING ON THE BODY OF CAPACITORS.

(i). understanding markings on the body of electrolytic capacitors.

Aluminum electrolytic capacitor.

Tantalum electrolytic capacitor.

SMD Tantalum electrolytic capacitor.

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(ii). understanding markings on the body of ceramic capacitors.

High voltage ceramic capacitor. Disc ceramic capacitor.

(iii). Understanding markings on the body of film capacitors.
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ENCODING MARKINGS ON NON-POLARIZED CAPCITORS BODY.

Non-polarized capacitors.eg ceramic and film capacitors normally have three digits used to indicate their capacitance
values. Here you can apply the same procedures for reading value of SMD resistors that uses three digits.ie the first
two digits indicates the significant digits and the last digit indicate the multiplier or number of zeros to be added to the
first two significant digits.
A letter may be used to indicate their tolerance.eg K, J, M etc. (check tolerance table).
The voltage rating for non-polarized capacitors are always indicated on their body either as that of electrolytic capacitors
or by using a mixed up of a number and a letter.eg 2A, 2G etc.
a). Metalized film.

Polyester.

Disc ceramic.
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For some capacitors, the voltage rating is shown directly on their body as in (a) above. For capacitors with voltage
rating shown by a mixed up of a number and a letter, consider the table below.

VOLTAGE RATING OF CAPACITORS (ceramic, film. etc.).

When a letter is used to indicate the tolerance/precision value, used the table below to find the tolerance value.
TOLERANCE.
LETTER TOLERANCE LETTER TOLERANCE
A ±0.05pF K ±10%
B ±0.10pF L ±15%
C ±0.25pF M ±20%
D ±0.5pF N ±30%
E ±0.5% P +100%, -0%
F ±1%
G ±2% Z +80%,-20%
H ±3%
J ±5%
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Examples on how to encode markings on body of non-polarized capacitors.

Example 1.
Here, the capacitor has capacitance value shown by 103, tolerance indicated by letter J and max-voltage of 1000V.
Therefore, the capacitance value can be calculated as shown below.
103. The first two digits (1 and 0) will be the significant digits and the third/last digit (3)
will be the multiplier/number of zeros to be added to the first two digits/value.

103=10 x𝟏𝟎𝟑 = 10 x 1000 = 10000pF.

But 10000pF = 10nF = 0.01µF.
Maximum voltage rating is 1000V = 1KV.
Example 2.
in this case, the capacitance value is given.ie 104 but the voltage rating is not indicated.
Here, the first two digits (1 and 0) will be the significant digits and the third digit (4) the number
of zeros to be added to the first two digits/value.ie 104 = 10 x𝟏𝟎𝟒 = 10 x 10000 = 100000pF =
100nF = 0.1µF

Example 3.
Here, the capacitance is given by 102, tolerance by letter J and max-voltage rating by 2A.

Capacitance value. 102 = 10 x𝟏𝟎𝟐 (two zeros to be added to 10).

Therefore, 102 = 1000pF = 1nF = 1µF.

Letter J from the tolerance table is ±5%

Voltage rating for 2A from the volt rating table =100V.

Example 4.
Here, the first two digits is 10 (significant digits) and the third digit is 2 which is the
multiplier/number of zeros to be added to 10.

Therefore, 102 = 10 x𝟏𝟎𝟐 = 1000pF = 1nF = 0.001µF.

1KV is the max-voltage rating and is 1000V.since K = 1000. From 1KV =1 X 1000 = 1000V.

Example 5.
Here, 224 is the value, K is the tolerance and 310 is the max-voltage rating in AC V.
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Therefore, 224 = 22 x𝟏𝟎𝟒 + 220000Pf = 220nF = 0.22µF.

Voltage rating = 310VAC.

Example 6.

105J450V. here, 105 = 10 x𝟏𝟎𝟓 = 1000000pF =1000nF = 1µF.

Voltage rating = 450V

Tolerance J = 5%.

CAPACITANCE ENCODING TABLE.

The table below will help you to know/encode the capacitance value of non-polarized capacitors.eg ceramic capacitors,
film capacitors etc.
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CAPACITOR INSTALLATION IN CIRCUIT BOARDS.

Capacitor type must be considered when installing in circuit board. The two types are non-polarized and polarized
capacitors. Non-polarized capacitors such as ceramic and film capacitors can be installed in circuit in either way or any
direction but in the case of polarized capacitors such as electrolytic (aluminum and tantalum), positive leg (anode) must
be connected to the positive rail and negative leg (cathode) must be connected to the negative rail (ground/GND). On
circuit board letter C is used to indicate the position of a capacitor.
The figures below show how polarized capacitors can be connected in circuit boards.

CAPACITORS COMMON FAILURE MODES.

Capacitor both polarized and non-polarized can fail in circuit due to various factors such as;
i. Over voltage.
ii. Over temperature.
iii. Reverse polarity (short circuit) etc.
These failure modes vary with the type of construction.
i. Output voltage drops.
When capacitors with filter function (electrolytic) has a problem say dried up, this usually causes voltage drop on that
line it is connected. The drying out of the electrolytes are normally caused by excessive heat (over temperature). This
drop-in voltage will cause low voltage problem (voltage fluctuation).
ii. Bulging.
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The bulging of electrolytic capacitors can be observed by looking at the top silvery part. If the top is swollen (bulged),
it is a sign that the maximum voltage rating of the capacitor was exceeded (over voltage).
NB: a capacitor with a swollen (bulged), raptured top is a sign of a bad capacitor. Therefore, it must be replaced.
Sometimes, the capacitor top may not look swollen. Therefore, it is advisable to also inspect the bottom part of the
capacitor.

If the bottom is swollen the capacitor must be replaced.

NB: Remember to replace any capacitor even if it has a slightly bulged top or bottom.

iii. Leakage.
This is common with electrolytic capacitors. They are relatively high leakage current capacitors when compared with
other types of capacitors since the oxide film layer is not a perfect insulator and allows current to leak through it when
voltage is applied. The value of this current mainly depends on applied voltage, capacitor temperature and duration of
operation. The amount of leakage current depends on the x-tics of the dielectric material and construction.
The current leakage through the dielectric can also cause short circuit between the terminals of the capacitor.
NB: also, when you see liquid (electrolytes) coming out of the capacitor’s top or bottom, just replace the capacitor
directly.
Capacitors rates high on the list of the major causes of problems in electronic devices. One reason being that all
electronic devices use clean DC supply to power different circuits. Capacitors plays a role in making sure the rectified
DC is free from ripples. So if a capacitor gets faulty (dry/swollen) it will not be able to do it work well and hence the
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circuit in which this capacitor is used will continue to get dirty DC. This will cause that circuit to get affected by this
unclean DC and eventually the components there will begin to fail.eg ICs, transistors etc.

CAPACITOR TESTING.

Testing capacitor is a big boost for technician since capacitors are usually the most caused of circuit failure. A capacitor
can be tested using an ERS meter (capacitance meter) or DMM set in resistance range. Besides, there are also other
ways of knowing (detecting) a faulty capacitor without using a meter. The following are ways of identifying a faulty
capacitor without testing.
(i). Visual inspection.
First scan around the circuit the circuit board looking for capacitor (electrolytic) which has its top silvery part swollen.
Even a slight bulged top is good enough evidence that the capacitor is faulty. In case, you see a swollen/slightly bulged
capacitor, don’t bother testing them but just replace them directly.
NB: also, when doing visual inspection, it is advisable to look/check the bottom part of the capacitor for bulging bottom
or fluid leakage. For ceramic capacitors, broken terminals, discoloration or burnt sign is an evidence that the capacitor
is faulty (bad) and you will have to replace it.

(ii). Capacitor getting hot.

This method may also work if the device is not functioning well but first make sure you put OFF the device and unplug
it from the power out let. Then depending on the circuit which you suspect to be causing the problem. You can quickly
touch the tops of the capacitors in that area and for any capacitor which is heating too fast (too hot) must be replaced.
NB: sometimes a capacitor gets too hot (blow) when there is a fault in the voltage supply line the capacitor is
connected.eg high voltage than capacitors rated voltage, shorted rectifier diodes (bridge rectifier), shorted Zener diode
etc. or a faulty (defective) component.eg IC, transistor etc. being supplied by the capacitor (connected after the
capacitor). Therefore, it is advisable to also check voltage supply line the capacitor is connected and the component
the capacitor is supplying before replacing the capacitor or incase the new capacitor installed also still gets hot after
replacement. This also works for swollen and blown capacitors.
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NB; don’t forget to check all components connected in line with the capacitor.

(iii). Output voltage drop.

This is another method of detecting/finding a faulty capacitor (dried up capacitors) but with the device connected to
power (turn ON).
If capacitor with filter functions develop a problem (dry) it usually causes voltage drop on that line.eg with DMM set in
DC voltage testing range if you measure a voltage to a circuit which has filter capacitor rated say 25V connected to
12V DC supply and you get less than 12Volt, this could point to a problem on the filter capacitor connected on that line.
This drops in output voltage may cause components in that line to fail since they are not receiving enough voltage
(energy) for their normal operation (working voltage).

TESTING CAPACITORS USING METERS.

Resistance test using Digital Multi-meters.
Testing electrolytic capacitors.
You can also use a digital multi meters set in resistance testing range to test or check a capacitor (electrolytic) if it is
faulty or not. The basic principle used is the capability of a capacitor to charge when current flows through its
lead. This test will only show if the capacitors is completely dead or not. It will not determine if the capacitor
is in good or poor condition. To check a cap in the resistance mode the following steps must be taken.
i). Remove the capacitor to be tested from the circuit board.

ii) Discharge the capacitor completely.

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(iii). Set the multi-meter to ohm (Ω) position and select the desired range for testing or checking the capacitors for
example select 20k for 100uF-470uF capacitors.

iv). Touch the multi-meter leads to the corresponding leads or the terminals of the capacitor.ie red test lead to anode
(+ terminal) and black test lead to the cathode (- terminal).

Current flow through the capacitor and capacitor starts charging. Multi-meter should show reading starting at 0Ω or
low resistance values then increases slowly (steady) and then go to infinity (over limit).ie “1” or “0L”.
If you reverse the test leads, it should do the same again. This means the capacitors is in working condition otherwise
it is not working. For instance, if the multi-meter stays at zero (000) the capacitor is not charging (short) meaning it is
faulty.
NB: you can also check for short between/across the capacitor’s terminals/leads with the multi meter set in either
resistance test mode or continuity test mode.eg ceramic chips and film capacitors.
If it reads continuity (short), low ohm and so on it is an evidence of a faulty capacitors.
A working ceramic chip capacitor usually reads infinity (open).ie”1” or” 0L”.

You can use the guide below when selecting the ohmic range for testing electrolytic capacitors.

Capacitance 0.1uF – 10uF 22uF – 68uF 100uF – 470uF 680uF – 10000uF

range 2000K 200K 20K 2K
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NB. The best way to test a capacitor is to use a capacitance meter or ESR meter as resistance test will not show if the
capacitor is within its working capacitance value.

CAPACITOR VOLTAGE TESTING (CHARGING).

Voltage test is done on capacitors (electrolytic) to see if a capacitor is working as normal by charging it up with a DC
voltage supply and then the voltage across the capacitor’s terminal is measured.
STEPS
i). Remove the capacitor from circuit
ii). Set the multi-meter to DC voltage test range.eg 20v, 200v and so on.
iii). Apply a voltage which is less than voltage rating of the capacitor to the capacitor for a few second.eg 25V rated
capacitor with 12V (the positive supply to anode and negative supply to cathode)

iv). Disconnect the capacitor from the voltage source and immediately measure the voltage across the terminals of the
capacitor with position test lead connected to anode and negative test lead to cathode.
The voltage at first should read the source voltage (12V) or whatever voltage you feed it and start to discharge its
voltage through the multi-meter in this case, the capacitors is working. If the capacitor does not store voltage (charge)
it is defective and should be replaced.
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CAPACITOR DISCHARGING. (How to discharge capacitors).

A capacitor such as high voltage rated electrolytic filter capacitors can hold charge for quite a long time after power is
OFF.
It is very important to make sure that there is no charge in the capacitor before testing otherwise it may destroy your
multi-meter (meter) or even harm you. Therefore, the following measures should be taken to discharge capacitors.
Low voltage rated capacitors.eg 25V, 16V, 10V, and so on can be discharged through connecting a low ohm resistor
of high watts.eg 10W across the capacitor’s terminals.

Using film resistor.

Using wire-wound resistor.

High voltage rated capacitors example 400V, 160V, 450V, 60V and so on you can discharge them by connecting a
dummy load bulb.eg 60W, 100W AC bulb and so on across the capacitors terminals.

NB. Do not use a screw driver, a wire or a low ohm resistor to discharge high voltage rated capacitors
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COMBINATION OF CAPACITORS
Capacitors arranged in series, parallel, parallel do not behave in the same way as resistors or indicator do when
arranged in similar combinations.
There are two important things to consider when connecting (combining) capacitors in circuits
i). Voltage rating of the capacitors
ii). Capacitance values of the capacitors
Remember capacitors stores charge temporary just like batteries. Therefore, capacitors behave just like batteries when
connected in series, parallel and series-parallel. Capacitors can be connected or combined in circuits in three ways; -
i). Series combination.
ii). Parallel combination.
iii). Series-parallel combination.

PARALLLEL COMBINATION OF CAPACITORS

Take the case of the three capacitors C1, C2 and C3 arranged in parallel as shown below.

If the voltage (V) is applied to the combination, each capacitor will get the same amount of voltage (V) (V=V1=V2=V3)
but the charge (Q) flowing into each capacitor will be proportional to its capacity (capacitance).
Total charge (Q) will be SUM of charges Q1, Q2 and Q3 taken by individual capacitor C1, C2 and C3 respectively that is
to say
𝑸
Q=Q1+Q2+Q3 …………………………. Equation (1). But from C= 𝑽 (capacitance formula)

Q=CV on cross multiply.

Now Q1=C1V, Q2=C2V and Q3=C3V
Replacing for Q1, Q2 and Q3 in Equation (1).
Q=Q1+Q2+Q3.
CV=C1V+C2V+C3V Taking common factor out
CV = V (C1+C2+C3)
Dividing both side by V
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C=C1+C2+C3
C=C1+C2+C3. Equation for Capacitance connected in parallel.
NB: when capacitors are connected in parallel, capacitance rating increases whereas voltage drops across each of
the capacitors remains the same example if 4µF capacitors is combined in parallel with 8µF capacitance of the
combination will be 12µF.
CIRCUIT CONNECTION OF CAPACITORS IN PARALLEL.
The diagram below shows how you can connect capacitors (PARALLEL) in circuit (power supply).
The capacitor here is connected with a filter function to remove ripples and provide a smooth DC output voltage.
To understand this well, let’s start by connecting a single electrolytic capacitor as shown below.
Schematic diagram.

Pictorial Diagram.

In the diagram above, the transformer (T) which is a step-down transformer will step down the AC voltage from 220VAC
to 12VAC.
The bridge rectifier work here is to rectify the 12VAC into pulsating 12VDC. The filter capacitor C1 connected in parallel
to the rectifier will then filter the pulsating DC into a smooth 12VDC.
NB: the capacitor must be connected in the correct polarity.ie positive supply to anode and negative supply (0V) to
cathode.
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Two capacitors in parallel.

Schematic diagram.

Pictorial Diagram.

As describe earlier, that the total capacitance for capacitors connected in parallel will be the SUM of the capacitance
value of the capacitors in the combination.ie C = C1+C2.
C = 2200µF + 2200µF = 4400µF.
Voltage drops across the combination will be the same.
NB; when connecting capacitors in parallel in circuit board, anode of all the capacitors are connected/soldered to the
positive supply rail and cathode of the capacitors are connected to the negative supply rail (0V). Otherwise, you will
destroy the capacitors.
Also take into consideration the voltage of the supply (voltage source) and make sure the voltage rating of the capacitor
is higher than that of the supply voltage.
It is advisable to use a capacitor that has its max-voltage rating twice the supply voltage. For instance, when you have
a 12VDC supply. Therefore, you will have to connect a 25V rated capacitor since 24V rated capacitor may not be
available. (12V x 2).
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SERIES COMBINATION OF CAPACITORS.

Consider three capacitors C1, C2 and C3 are arranged in series as shown below.

If voltage V is applied to the combination, the total voltage V is the SUM of voltages V1, V2 and V3 across individual
capacitor C1, C2 and C3 respectively.
When capacitors are connected in series, the same current will flow through each capacitor and each capacitor will get
the same charge Q.ie Q = Q1 = Q2 = Q3.
Calculating for voltage V.
It is said that, SUM of voltage drops across individual capacitor equals the voltage V applied (source voltage).
V = V1+V2+V3 ………………………………………………………. eqn.1.
𝑸
But from C= (capacitance formula)
𝑽
𝑸
V=
𝑪

𝑸 𝑸 𝑸 𝑸
Now, V = , V1= , V2= and V3= .
𝑪 𝑪𝟏 𝑪𝟐 𝑪𝟑
Replacing for V, V1, V2 and V3 in equation 1.
𝑸 𝑸 𝑸 𝑸
= + + .
𝑪 𝑪𝟏 𝑪𝟐 𝑪𝟑
Taking the common factor out.
𝟏 𝟏 𝟏 𝟏
Q( )=Q( + + )
𝑪 𝑪𝟏 𝑪𝟐 𝑪𝟑
Dividing both side by Q.
𝟏 𝟏 𝟏 𝟏
= + + .
𝑪 𝑪𝟏 𝑪𝟐 𝑪𝟑
. Equation for capacitance in series combination.
For two capacitors arrange in series, the total capacitance is calculated using the formulas below.

𝟏 𝟏 𝟏 𝑪𝟏𝑪𝟐
= + OR C =
𝑪 𝑪𝟏 𝑪𝟐 𝑪𝟏+𝑪𝟐
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NB: when capacitors are arranged in series, voltage rating increases while capacitance remains as that of a single
capacitor.ie voltage across the capacitors add up.

Circuit connection of capacitors in series.

A center tapped linear transformer will become useful when you want to connect capacitors in series in circuit especially
when building power supply. The capacitors function here is filtering the pulsating DC into a smooth DC.

Using two electrolytic capacitors of same rating and size.

Schematic diagram.
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Actual Diagram.

NB: in practice, capacitors are usually connected in series when there is need to get +V, -V and GND/0V needed to
run a device that requires both –V and +V and GND for its operation. The –V and +V is tested with respect to GND/0V.
In the diagram above (schematic diagram), if C1 and C2 are rated 25V 2200µF each and the voltage of the supply is
15VDC.
BC will give -15VDC with respect to GND/0V (point B).
AB will give +15VDC with respect to GND/0V (point B).
AC will give 30VDC with respect to point A (-V) acting as the ground point (GND/0V) and this is the reason why it is
said that, voltage increases when capacitors are connected in series.
The capacitance in the circuit will remain 2200µF.

SERIES-PARALLEL COMBINATION OF CAPACITORS.

When capacitors are connected in series-parallel, both voltage and capacitance increase.
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NB: to calculate total capacitance for capacitors arranged in series-parallel, start by calculating the capacitance for
capacitors connected in series and then parallel.

Series-parallel connection of capacitors in circuit.

Using four electrolytic capacitors.
This will require a center tapped transformer to provide ground/GND (0V) or common point.

When capacitors are connected in series-parallel combination, both voltage and capacitance will increase.
In the diagram above, consider C1 – C4 having 25V 2200µF each.
At AC voltage will be 50V 4400µF.
How it is calculated.
C1 and C2 are connected in series which gives 50V 2200µF.
C3 and C4 are also connected in series and gives 50V 2200µF.
It will become like two capacitors rated 50V 2200µF connected in parallel. Therefore, the combination will give 50V
4400µF.
NB: in practice, it is the voltage of the supply that increases NOT the voltage of the capacitors.
NB: 1. in practice, it is NOT the voltage of the capacitors that will be measured across the circuit but it is the voltage of
the supply. This voltage (supply voltage) may be the exact voltage or a higher voltage than the supply voltage when
measured across the capacitors. This is because the capacitor/s will store charge when voltage is applied to it.
2. When connecting capacitors in series, parallel and series-parallel, make sure the capacitors are of the same
rating and size.
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Reference.

• Introduction to electronics. By Hassan Mehmood Khan.

• Grob’s basic electronic 12e. by Mitchel E. Schultz.
• Basic radio and television 2nd e. SP Sharma.
• Electronic fundamentals circuit, device and applications. 8th e. by Thomas L.Floyd. David Buchla.
• Art of electronics.
• Research from internet.
NB. This book is made for training students on electronic repair under NERS electronic device repair training
programs.