Electrical Circuits

AN ELECTRICAL CIRCUIT

The circuit shown below has a power source, fuse, switch, two lamps and wires connecting each into a loop or circle. When the connection is complete, current flows from the positive terminal of the battery through the wire, the fuse, the switch, another wire, the lamps, a wire and to the negative terminal of the battery. The route along which the electricity flows is called an electrical circuit.

ELECTRICAL CIRCUIT REQUIREMENTS

A complete Electrical Circuit is required in order to make electricity practical. Electrons must flow from and return to the power source.

There are three different circuit types, all require the same basic components:

1. Power Source is needed to supply the flow of electrons (electricity).

2. Protection Device prevents damage to the circuit in the event of a short. 

3. Load Device converts the electricity into work.

4. Control Device allows the user control to turn the circuit on or off

5. Conductors provide an electrical path to and from the power source.

BASIC CIRCUIT CONSTRUCTION1. Power Source (Battery, Alternator, Generator, etc.) 2. Protection Device (Fuse, Fusible Link, or Circuit Breaker) 3. Load Device (Lamp, Motor, Winding, Resistor, etc. 4. Control (Switch, Relay, or Transistor) 5. Conductors (A Return Path, Wiring to Ground)

LOADS

The illustration below has a horn in place of the lamp. Any device such as a lamp, horn, wiper motor, or rear window defogger, that consumes electricity is called a load. In an electrical circuit, all loads are regarded as resistance. Loads use up voltage and control the amount of current flowing in a circuit. Loads with high resistance cause less current to flow while those with lower resistance allow high current rates to flow.

AUTOMOTIVE ELECTRICAL CIRCUITS

In an automotive electrical circuit, one end of the wire from each load returning to the battery is connected to the vehicle body or frame. Therefore, the vehicle body or frame itself functions as a conductor, allowing current to flow though the body or frame and back to the battery. The body or frame is then referred to as the body ground (or earth) of the circuit (meaning that part of the circuit that returns the current to the battery).

WHAT IS OHM'S LAW?

A simple relationship exists between voltage, current, and resistance in electrical circuits. Understanding this relationship is important for fast, accurate electrical problem diagnosis and repair.

OHM'S LAW

Ohm's Law says: The current in a circuit is directly proportional to the applied voltage and inversely proportional to the amount of resistance. This means that if the voltage goes up, the current flow will go up, and vice versa. Also, as the resistance goes up, the current goes down, and vice versa. Ohm's Law can be put to good use in electrical troubleshooting. But calculating precise values for voltage, current, and resistance is not always practical ... nor, really needed. A more practical, less time-consuming use of Ohm's Law would be to simply apply the concepts involved:

SOURCE VOLTAGE is not affected by either current or resistance. It is either too low, normal, or too high. If it is too low, current will be low. If it is normal, current will be high if resistance is low, or current will be low if resistance is high. If voltage is too high, current will be high.

CURRENT is affected by either voltage or resistance. If the voltage is high or the resistance is low, current will be high. If the voltage is low or the resistance is high, current will be low.

RESISTANCE is not affected by either voltage or current. It is either too low, okay, or too high. If resistance is too low, current will be high at any voltage. If resistance is too high, current will be low if voltage is okay.

NOTE: When the voltage stays the same, such as in an Automotive Circuit... current goes up as resistance goes down, and current goes down as resistance goes up. Bypassed devices reduce resistance, causing high current. Loose connections increase resistance, causing low current.

OHM'S LAW FORMULA

When voltage is applied to an electrical circuit, current flows in the circuit. The following special relationship exists among the voltage, current and resistance within the circuit: the size of the current that flows in a circuit varies in proportion to the voltage which is applied to the circuit, and in inverse proportion to the resistance through which it must pass. This relationship is called Ohm's law, and can be expressed as follows:

E = I R

Voltage = Current x Resistance

E Voltage applied to the circuit, in volts (V)I Current flowing in the circuit, in amperes (A) R Resistance in the circuit, in ohms

In practical terms "V = I x R" which means 

"Voltage = Current x Resistance".

1 volt will push one amp through 1 ohm of resistance.

NOTE: E = IR, V=AR, or V=IR are all variations of the same formula. How you learned Ohm's law will determine which one you will use. Personal preference is the only difference; anyone will get you the correct answer.

OHM'S LAW SYMBOL SHORTCUT

Mathematical formulas can be difficult for many who don't use them regularly. Most people can remember a picture easier than a mathematical formula. By using the Ohms law symbol below, anyone can remember the correct formula to use. By knowing any two values you can figure out the third. Simply put your finger over the portion of the symbol you are trying to figure out and you have your formula.

APPLICATIONS OF OHM'S LAW

As an application of Ohm's law, any voltage V, current I or resistance R in an electrical circuit can be determined without actually measuring it if the two others values are known.

This law can be used to determine the amount of current I flowing in the circuit when voltage V is applied to resistance R. As stated previously, Ohm's law is:

Current = Voltage / Resistance.

In the following circuit, assume that resistance R is 2 and voltage V that is applied to it is 12 V. Then, current I flowing in the circuit can be determined as follows:

This law can also be used to determine the voltage V that is needed to permit current I to pass through resistance R: V = I x R (Voltage= Current x Resistance).

In the following circuit, assume that resistance R is 4 ohms. The voltage V that is necessary to permit a current I of 3 A to pass through the resistance can be determined as follows:

Still another application of the law can be used to determine the resistance R when the voltage V which is applied to the circuit and current I flowing in the circuit are already known:

In the following circuit, assume that a voltage V of 12 V is applied to the circuit and current I of 4 A flows in it. Then, the resistance value R of the resistance or load can be determined as follows:

TYPES OF CIRCUITS 

Individual electrical circuits normally combine one or more resistance or load devices. The design of the automotive electrical circuit will determine which type of circuit is used. There are three basic types of circuits:

Series Circuit

Parallel Circuit

Series-Parallel Circuit

SERIES CIRCUITS

A series circuit is the simplest circuit. The conductors, control and protection devices, loads, and power source are connected with only one path to ground for current flow. The resistance of each device can be different. The same amount of current will flow through each. The voltage across each will be different. If the path is broken, no current flows and no part of the circuit works. Christmas tree lights are a good example; when one light goes out the entire string stops working.

SERIES CIRCUITS

A Series Circuit has only one path to ground, so electrons must go through each component to get back to ground. All loads are placed in series.

Therefore:

1. An open in the circuit will disable the entire circuit.

2. The voltage divides (shared) between the loads.

3. The current flow is the same throughout the circuit.

4. The resistance of each load can be different.

SERIES CIRCUIT CALCULATIONS

If, for example, two or more lamps (resistances R1 and R2, etc.) are connected in a circuit as follows, there is only one route that the current can take. This type of connection is called a series connection. The value of current I is always the same at any point in a series circuit.

The combined resistance RO in this circuit is equal to the sum of individual resistance R1 and R2. In other words: The total resistance(RO) is equal to the sum of all resistances (R1 + R2 + R3 + .......)

Therefore, the strength of current (I) flowing in the circuit can be found as follows:

Resistance R0 (a combination of resistances R1 and R2, which are connected in series in the circuit as illustrated) and current I flowing in this circuit can be determined as follows:

VOLTAGE DROP

A voltage drop is the amount of voltage or electrical pressure that is used or given up as electrons pass through a resistance (load). All voltage will be used up in the circuit. The sum of the voltage drops will equal source voltage. A voltage drop measurement is done by measuring the voltage before entering the load and the voltage as it leaves the load. The difference between these two voltage readings is the voltage drop.

VOLTAGE DROP TOTAL

When more than one load exists in a circuit, the voltage divides and will be shared among the loads. The sum of the voltage drops equal source voltage. The higher the resistance the higher the voltage drop. Depending on the resistance, each load will have a different voltage drop.

0V + 5V + 7V + 0V = 12V

VOLTAGE DROP CALCULATION

When current flows in a circuit, the presence of a resistance in that circuit will cause the voltage to fall or drop as it passes through the resistance. The resultant difference in the voltage on each side of the resistance is called a voltage drop. When current (I) flows in the following circuit, voltage drops V1 and V2 across resistances R1 and R2 can be determined as follows from Ohm's law. (The value of current I is the same for both R1 and R2 since they are connected in series.)

The sum of the voltage drops across all resistances is equal to the voltage of the power source (VT):

The voltage drop across resistances R1 and R2 in the following circuit can be determined as follows:

PARALLEL CIRCUIT

A parallel circuit has more than one path for current flow. The same voltage is applied across each branch. If the load resistance in each branch is the same, the current in each branch will be the same. If the load resistance in each branch is different, the current in each branch will be different. If one branch is broken, current will continue flowing to the other branches.

PARALLEL CIRCUITS

A Parallel Circuit has multiple paths or branches to ground. Therefore:

1. In the event of an open in the circuit in one of the branches, current will continue to flow through the remaining.

2. Each branch receives source voltage.

3. Current flow through each branch can be different.

4. The resistance of each branch can be different.

PARALLEL CIRCUIT

In parallel connection, two or more resistances (R1, R2, etc.) are connected in a circuit as follows, with one end of each resistance connected to the high (positive) side of the circuit, and one end connected to the low (negative) side. Full battery voltage is applied to all resistances within a circuit having a parallel connection.

Resistance R0 (a combination of resistances R1 and R2) in a parallel connection can be determined as follows:

From the above, the total current I flowing in this circuit can be determined from Ohm's law as follows:

The total current I is also equal to the sum of currents I1 and I2 flowing through individual resistances R1 and R2

Since battery voltage V is applied equally to all resistances, the strength of currents I1 and I2 can be determined from Ohm's law as follows:

Resistance RO (a combination of resistances R1 and R2, which are connected in parallel in the circuit as shown below), the total current I flowing in the circuit, and currents I1 andI2 flowing through resistances R1 and R2, can be determined respectively as follows:

SERIES PARALLEL CIRCUIT

A series-parallel circuit has some components in series and others in parallel. The power source and control or protection devices are usually in series; the loads are usually in parallel. The same current flows in the series portion, different currents in the parallel portion. The same voltage is applied to parallel devices, different voltages to series devices. If the series portion is broken, current stops flowing in the entire circuit. If a parallel branch is broken, current continues flowing in the series portion and the remaining branches.

SERIES-PARALLEL CIRCUIT

A resistance and lamps may be connected in a circuit as illustrated below. This type of connecting method is called series-parallel connection, and is a combination of series and parallel connections. The interior dash board lights are a good example. By adjusting the rheostat, you can increase or decrease the brilliance of the lights.

The combined resistance R02 in this series-parallel connection can be determined in the following order:

a. Determine combined resistance R01, which is a combination of resistances R2 and R3 connected in parallel.

b. Then, determine resistance R02, which is a combination of resistance R1 and combined resistance R01 connected in series.

Total current I flowing in the circuit can be determined from Ohm's law as follows:

The voltage applied to R2 and R3 can be found by the following formula:

Currents I1, I2 and I flowing through resistances R1, R2 and R3 in the series-parallel connection, as shown below, can be determined as follows:

Electrical Fundamentals

MATTER

Everything in the world is made of matter. Matter is anything that has mass (weight) and occupies space.

Matter can be made up of a group or series of different atoms to form a molecule. These groups of atoms (molecules) are sometimes called compounds. Some types of matter can be broken down to a single atom while still maintaining the properties of the original material. These types of material are called elements.

Matter has three states: Solid, Liquid, and Vapor.

MOLECULE EXAMPLE

Imagine a lake. Now imagine taking the smallest particle or piece of water from the lake. You would have a single molecule of water, H₂O, which is made up of two hydrogen atoms and one oxygen atom.

Not all materials are made up of molecules. Copper, for example, is made up of a single copper atom. These are called elements. Each element is a type of matter that has certain individual characteristics.

THE ATOM One of the basic building blocks in the universe for matter is the atom. All matter - gas, liquid, or solid - is made up of molecules or atoms joined together. These atoms are the smallest particle into which an element or substance can be divided without losing its property. A single atom consists of three basic components: a proton, a neutron, and an electron. Within the atom there is a Nucleus. The Nucleus contains the protons and neutrons. Orbiting around the nucleus are the electrons. An atom is similar to a miniature solar system. As with the sun in the center of the universe, the nucleus is in the center of the atom. Protons and Neutrons are contained inside the nucleus. Orbiting around the nucleus are the electrons. ATOM CONSTRUCTIONAn atom is similar to a miniature solar system. As the sun is in the center of the solar system, so is the nucleus is in the center of the atom. Protons and neutrons are contained within the nucleus. Electrons orbit around the nucleus, which would be similar to planets orbiting around the sun. NUCLEUSThe Nucleus is located in the center of the atom (shown in red). The Nucleus contains the protons and neutrons. Orbiting around the nucleus are the electrons. PROTONS Protons are located within the nucleus of the atom (shown in blue). Protons are positively (+) charged. NEUTRONS  Neutrons add atomic weight to an atom (shown in green). Neutrons have no electrical charge. ELECTRONSElectrons orbit around the nucleus of the atom (shown in yellow). Electrons are negatively (-) charged. Since electrons are lighter than protons and are outside the nucleus, they can be easily moved from atom to atom to form a flow of electrons. Normally electrons are prevented from being pulled into the atom by the forward momentum of their rotation. Electrons are also prevented from flying away because of the magnetic attraction of the protons inside the nucleus, the same type of force that keeps the planets orbiting around the sun. ELECTRICAL CHARGES Opposite electrical charges always attract each other. So these particles with opposite charges will tend to move toward each other. Like electrical charges always repel. So particles with like charges will move away from each other. Remember: Opposites charges attract, and like charges repel. Atoms always try to remain electrically balanced. BALANCED ATOMSAtoms normally have an equal number of electrons and protons.Atoms have no electrical charge. They are neither positive nor negative. They are electrically neutral or BALANCED.The negative charge of the electrons will cancel the positive charge of the protons, thus balancing the charge of the atom. This cancellation of charges creates a natural attraction or bonding between the positive proton and the negative electron. ION PARTICLESWhen an atom loses or gains an electron, an imbalance occurs. The atom becomes either a positively or negatively charged particle called an ION. These unbalanced charged ION particles are responsible for electron flow (electricity). IONs will take or release an electron to become balanced again. ION CHARGEA positive (+) ION has one less electron than it has protons. A negative (-) ION has one more electron than it has protons. The positive ION attracts a negative ION to become balanced. This attraction or difference in electrical potential causes electron flow. ELECTRON ORBITSElectrons rotate around the atom at different orbits called Rings, Orbits, or Shells. BOUND ELECTRONS orbit the nucleus on the inner rings. Bound electrons have a strong magnetic attraction to the nucleus. FREE ELECTRONS orbit on the outermost ring which is known as the VALANCE RING. FREE ELECTRONSOnly the FREE ELECTRONS in the outermost shell (Valance Ring) are free to move from atom to atom. This movement is called ELECTRON FLOW. These FREE ELECTRONS are loosely held and can easily be moved to another atom or ion. Because of their distance from the nucleus, free electrons have a weak magnetic attraction. Since this attraction is not as strong to the nucleus as the bound electrons on the inner orbits, the electrons move easily from atom to atom. INSULATORSAn INSULATOR is any material that inhibits (stops) the flow of electrons (electricity). An insulator is any material with 5 to 8 free electrons in the outer ring.Because, atoms with 5 to 8 electrons in the outer ring are held (bound) tightly to the atom, they CANNOT be easily moved to another atom nor make room for more electrons. Insulator material includes glass, rubber, and plastic.

CONDUCTORSA CONDUCTOR is any material that easily allows electrons (electricity) to flow. A CONDUCTOR has 1 to 3 free electrons in the outer ring.Because atoms with 1 to 3 electrons in the outer ring are held (bound) loosely to the atom, they can easily move to another atom or make room for more electrons. Conductor material includes copper and gold.

SEMICONDUCTORSAny material with exactly 4 free flectrons in the outer orbit are called SEMICONDUCTORS. A semiconductor is neither a conductor or insulator. semiconductor material includes carbon, silicon, and germanium. These materials are be used in the manufacturer of diodes, transistors, and integrated circuit chips.

Two Current Flow theories exist. The first is: ELECTRON THEORY The Electron Theory states that current flows from NEGATIVE to POSITIVE. Electrons move from atom to atom as they move through the conductor towards positive.

The second Current Flow theory is: CONVENTIONAL THEORY Conventional theory, also known as HOLE THEORY, states that current flows from POSITIVE to NEGATIVE. Protons or the lack of electrons (the holes) move towards the negative. (Current flow direction in Hole Theory is the opposite of that in Electron Theory.)

VOLTAGE Voltage is the electrical force that moves electrons through a conductor. Voltage is electrical pressure also known as EMF (Electro Motive Force) that pushes electrons. The greater the difference in electrical potential push (difference between positive and negative), the greater the voltage force potential.

MEASUREMENT A VOLTMETER measures the voltage potential across or parallel to the circuit. The Voltmeter measures the amount of electrical pressure difference between two points being measured. Voltage can exist between two points without electron flow. VOLTAGE UNITSVoltage is measured in units called VOLTS. Voltage measurements can use different value prefixes such as millivolt, volt, Kilovolt, and Megavolt. VOLTAGE LESS THAN BASE UNIT BASIC UNIT LARGER THAN BASE UNIT Symbol mV V kV Pronounced millivolt Volt Kilovolt Multiplier 0.001 1 1,000 CURRENT (AMPERES) CURRENT is the quantity or flow rate of electrons moving past a point within one second. Current flow is also known as amperage, or amps for short. Higher voltage will produce higher current flow, and lower voltage will produce lower current flow. MEASUREMENTAn AMMETER measures the quantity of current flow.Ammeters are placed in series (inline) to count the electrons passing through it. Example: A water meter counts the gallons of water flowing through it. AMPERAGE UNITSCurrent flow is measured in units called Amperes or AMPS. Amperage measurements can use different value prefixes, such as microamp, milliamp, and Amp. AMPERAGE LESS THAN BASE UNIT LESS THAN BASE UNIT BASIC UNIT Symbol µA mA A Pronounced Microamp milliamp Amp Multiplier 0.000001 0.001 1 AFFECTS OF CURRENT FLOWTwo common effects of current flow are Heat Generation and Electromagnetism. HEAT: When current flows, heat will be generated. The higher the current flow the greater the heat generated. An example would be a light bulb. If enough current flows across the filament, it will glow white hot and illuminate to produce light. ELECTROMAGNETISM: When current flows, a small magnetic field is created. The higher the current flow, the stronger the magnetic field. An example: Electromagnetism principles are used in alternators, ignition systems, and other electronic devices. RESISTANCEResistance is the force that reduces or stops the flow of electrons. It opposes voltage. Higher resistance will decrease the flow of electrons and lower resistance will allow more electrons to flow. MEASUREMENTAn OHMMETER measures the resistance of an electrical circuit or component. No voltage can be applied while the ohmmeter is connected, or damage to the meter will occur. Example: Water flows through a garden hose, and someone steps on the hose. The greater the pressure placed on the hose, the greater the hose restriction and the less water flows. RESISTANCE UNITSResistance is measured in units called OHMS. Resistance measurements can use different value prefixes, such as Kilo ohm and Megaohms. AMPERAGE BASIC UNIT MORE THAN BASE UNIT MORE THAN BASE UNIT Symbol K M Pronounced Ohm Kilo ohm Megaohm Multiplier 1 1,000 1,000,000 RESISTANCE FACTORS Various factors can affect the resistance. These include: LENGTH of the conductor. The longer the conductor, the higher the resistance. DIAMETER of the conductor. The narrower the conductor, the higher the resistance. TEMPERATURE of the material. Depending on the material, most will increase resistance as temperature increases. PHYSICAL CONDITION (DAMAGE) to the material. Any damage will increase resistance. TYPE of MATERIAL used. Various materials have a wide range of resistances. TYPES OF ELECTRICITY Two basic types of Electricity classifications: STATIC ELECTRICITY is electricity that is standing still. Voltage potential with NOelectron flow. DYNAMIC ELECTRICITY is electricity that is in motion. Voltage potential WITH electron flow. Two types of Dynamic electricity exist: Direct Current (DC) Electron Flow is in only one direction. Alternating Current (AC) Electron flow alternates and flows in both directions (back and forth). STATIC ELECTRICITY Voltage potential with NO electron flow. Example: By rubbing a silk cloth on a glass rod, you physically remove electrons from the glass rod and place them on the cloth. The cloth now has a surplus of electrons (negatively charged), and the rod now has a deficiency of electrons (positively charged). Another example: Rub your shoes on a rug and then touch a metal table or chair .... Zap!! The shock you felt was the static electricity dissipating through your body. DYNAMIC ELECTRICITY is electricity in motion, meaning you have electrons flowing, in other words voltage potential WITH electron flow. Two types of dynamic electricity exists: Direct Current (DC) Alternating Current (AC) DIRECT CURRENT (DC) Electricity with electrons flowing in only one direction is called Direct Current or DC. DC electrical systems are used in cars. ALTERNATING CURRENT (AC) Electricity with electrons flowing back and forth, negative - positive- negative, is called Alternating Current, or AC. The electrical appliances in your home use AC power. SOURCES OF ELECTRICITYElectricity can be created by several means: Friction, Heat, Light, Pressure, Chemical Action, or Magnetic Action. Only a few of these sources of energy are used in the automobile. The battery produces electricity through chemical action, and the alternator produces electricity through magnetic action. Friction creates static electricity. Heat can act upon a device called a thermo couple to create DC. Light applied to photoelectric materials will produce DC electricity. Pressure applied to a piezoelectric material will produce DC electricity. Chemical Action of certain chemicals will create electricity.