Basic Electrical pdf file

Electrical Basics “Chasing Sparks”

What is Electricity? Everything that has substance and takes up space, whether it is solid, liquid, or gaseous, is made up of very small particles called atoms.

What is Electricity? Scientists believe all atoms have negatively charged particles known as electrons, which revolve around a central core, or nucleus. This nucleus is believed to be positively charged, and to contain other particles known as protons and neutrons.

What is Electricity? Electrons in the inner orbit or orbits are known as bound electrons. Those in the outer orbit are called free electrons, and can be easily forced out of their orbits, flowing from one atom to another.

Current Flow The “electron theory” states that current flow is the organized, forced movement of free electrons in a specific direction. Continuous current flow in only one direction is known as “DC” or “Direct Current.”

Current Flow Flow that alternates back and forth is called “Alternating Current.”

A good conductor is a material that has many free electrons, such as copper. Lead and gold have large numbers of free electrons.

Current Flow Good conductors readily transmit electricity. The force that causes electrons to move from one atom to another is called electromotive force (EMF).

Current Flow Electromotive force is caused by a difference in electrical potential and is measured in volts, also referred to as voltage.

Current Flow When electrons begin to flow, the effect is felt instantly all along the surface of the conductor, very much as force can be felt all the way through a row of billiard balls.

Current Flow Some older cars and heavy equipment had their positive battery terminal connected to the chassis or frame and the negative side of the circuit was switched. Practically no production vehicle uses this configuration today.

Current Flow Today’s vehicles have their negative terminal battery terminal connected to the chassis or frame, also known as ground. The positive feed wires to vehicle components all originate at the positive battery terminal

Current Flow When a switch is closed, current flows from the battery negative post to chassis ground, through the load and switch, and to the positive terminal.

Current Flow Even though the ground has the excess of electrons, the positive post is the one that is generally regarded as “hot.”

Current Flow “Electron theory” theory supposes current flow to be from negative to positive, while “Conventional Theory” supposes the current flows from positive to negative.

Current Flow Thus, the current in automotive circuits is usually traced from the source (battery) to the load (bulb, motor, etc.) and then to ground.

Sources of Electricity A battery is a chemical source of electricity. It contains a number of positive plates and an equal number of negative plates.

Sources of Electricity The positive and negative plates are immersed in an electrolyte solution composed of water and sulphuric acid.

Sources of Electricity When the battery is charged, a chemical reaction of the acid on the plates results in an excess of electrons collecting on the negative plates.

Sources of Electricity If a conductor is connected between the plates, current (electrons) will flow through the conductor from one plate to the other.

Electromagnetic Induction When a conductor connected to a closed circuit is passed through a magnetic field, current is produced in the conductor.

Electromagnetic Induction Alternators, generators, and various inductive sensors use this principle to do their work.

Static Electricity Electrons can move from one body of matter to another by friction. Scuffing your shoes on carpet on a cold, dry day can cause a nice zap!

Lightning is another form of static electricity discharging from the atmosphere to the earth.

Electrical Circuits

Electrical Circuits

An electrical circuit is a complete path for current flow… basically defined as being froma power source to a load component that has resistance and uses electricity to do its work, and finally a ground path back to the negative terminal of the power source.

Circuit Components One component necessary for all circuits is a power

source.

In an automobile, the power source is the battery when the engine is switched off and the alternator when the engine is running..

Circuit Components Conductors are wires and cables, usually protected from each other and ground by insulation, and they carry the current in an electrical circuit.

Circuit Components Note: In an automotive circuit, the vehicle chassis and the engine block are actually conductors in the circuit.

Circuit Components

Controls (switches) are necessary to turn the circuit on and off.

Circuit Components The Load is a device that uses up electricity and turns it into work. Light bulbs and motors are among the examples of loads in an automotive circuit

Circuit Components The Circuit Protector is a device that protects the conductors and components in a circuit in case of an overload.

Current Will Flow IF... • The switch is closed • The circuit protector is not open • Charge is available

Ohm’s Law Ohm’s Law is the basic rule for the relationships between voltage, current, and resistance.

1. CURRENT FLOW IS DIRECTLY PROPORTIONAL TO VOLTAGE 2. CURRENT FLOW IS INVERSELY PROPORTIONAL TO RESISTANCE

Ohm’s Law 1. CURRENT FLOW IS DIRECTLY PROPORTIONAL TO VOLTAGE: Simply put, this means that an increase in VOLTAGE will cause an INCREASE in current flow. This is true because voltage is, in effect, electrical “pressure.” The higher the voltage, the higher the pressure, thus the higher the current flow. Remember:

1 volt pushes 1 amp through 1 ohm.

Ohm’s Law 2. CURRENT FLOW IS INVERSELY PROPORTIONAL TO RESISTANCE

This statement means that an increase in RESISTANCE will cause a DECREASE in current flow.

Ohm’s Law High current flow…

Added resistance… Lower Current flow

Ohm’s Law Voltage equals

Current

E

“ ” is used to denote volts.

times

Resistance

I

“ ” denotes current.

R” denotes

“

resistance.

Ohm’s Law 1 volt pushes 1 amp through 1 ohm, right? Okay, how many amps will 12 volts push through 6 ohms?

Resistance — 2 ohms

Resistance — 2 ohms

Draw — 5 Amps

Draw — 6 Amps

10 volts

12 volts

Voltage is like Pressure

Voltage is like Pressure NOTE: Increasing voltage in a given circuit

always

increases current draw.

Voltage is like Pressure Voltage is also expressed as a “difference in potential” when it refers to electromotive force caused by a difference in electrical charges between two points in a circuit.

Current Current is the flow of electrons between two points in a closed circuit that have a difference in potential.

Current The unit of measurement to determine current flow is the ampere (abbreviated “amp”).

Current One ampere is defined as the movement of one coulomb of electrons past a given point in one second. A coulomb is one billion billion electrons.

Current Current is thus a measure of the rate of electrical flow. It can also be known as amperage or draw, and is measured with an ammeter.

Current When two loads are connected parallel, as in the illustration on the left, each draws current independently of the other.

Current In the picture, bulb A draws 2 amps, while bulb B draws 1 amp. The total current flow in the circuit is 3 amps.

Current In the picture, bulb A draws 2 amps, while bulb B draws 1 amp. The total current flow in the circuit is 3 amps.

Current Important: The total current draw in a parallel circuit equals the sum of the individual current draws.

Current If the same two bulbs are connected in series instead of parallel, their combined resistance will be 18 ohms.

Current

0.67 amps X 18 ohms = 12 v 12 v/ 18 ohms = 0.67 amps

Resistance

Resistance Resistance is an opposition to current flow offered by a load or a resistor.

Resistance Even conductors have some resistance; for example, a piece of 22 gauge copper wire 60 feet long has one ohm of resistance. Larger diameter wires have less resistance.

Resistance

Heat generally causes resistance to increase in a conductor or connection.

Resistance An interesting and somewhat volatile relationship exists between heat and resistance in electrical wiring…

Resistance Since every connection has some resistance, that resistance produces heat…

Resistance …and that heat produces more resistance, which in turn produces more heat until current finally stops flowing and the component fails.

Resistance

When resistors are in series, the total resistance is the sum of the individual resistances… 6+6 = 12

Resistance

When resistors are in parallel, the total resistance equals the source voltage divided by the combined current draw.

Resistance

With a 12 volt supply, how much amperage would each of these resistors pull?

Resistance

Resistance

So each 6 ohm resistor will pull 2 amps. And 2 + 2 = 4

Resistance

Okay, if the total circuit pulls 4 amps, how many ohms of resistance would the total circuit have, based on a 12 volt supply?

Resistance

Resistance

Resistance

Resistance

Let’s try a different combination. With a 12 volt source, how much total resistance would this parallel circuit have?

Resistance

_______________Amps +_______________Amps Equals __________Amps total.

Resistance

Resistance

Resistance

Voltage Drop It’s a basic rule for closed circuits that the voltage “used up” or “dropped” in the loads must be equal to the source voltage.

Voltage Drop The voltmeter at point A will measure the source voltage. If the voltage measurement is taken at point B, what will the voltage be?

Voltage Drop Did you say zero volts? You’d be right. The voltage drop is equal to 12 times zero, which comes to zero volts.

Voltage Drop When two or more loads are in series: 1. The voltage drop of each load is equal to current draw times resistance. (E = I X R)

Voltage Drop 2. The sum of all voltage drops equals the source voltage.

Voltage Drop That is, the closer you move your probe to the ground side of a circuit...

Voltage Drop …the lower the measured voltage will be.

Voltage Drop Thus in the example shown here: Total Resistance = 6 ohms, and draw = 2 amps.

Voltage Drop The voltage drop at the brightness control is 2 amps x 3 ohms, which equals 6 volts.

Voltage Drop Thus available voltage to the bulb is only 6 volts

Computing Parallel Resistances by Formula

Computing Parallel Resistances by Formula If all the resistances are equal, divide the resistance of one alone by the number of resistors.

Computing Parallel Resistances by Formula In this example,

12/4 = 3 ohms resistance.

Computing Parallel Resistances by Formula If there are only two resistances, multiply their values and divide by the sum of their values.

Computing Parallel Resistances by Formula

In this example:

Computing Parallel Resistances by Formula For any three or more resistances, first find their “reciprocals,” then add the reciprocals together and divide the total by one.

Computing Parallel Resistances by Formula In this example:

Power Sources and Grounds

Power Sources The storage battery provides current to all electrical systems when the key is on and the engine is off.

Power Sources The generator maintains the charge in the battery after the engine is started and supplies electrical current to all electrically powered equipment.

Grounds Case Grounds are used where the component itself is securely attached to a well-grounded part of the vehicle.

Grounds Remote Grounds are used where the component itself is not grounded...

Grounds ...or where the remote ground is used to control the component. Examples are reversible motors (power windows, door locks) and instrument panel warning indicator lamps.

Reading Schematics

Basic Rule: The top of most schematics is usually “hot” and the bottom is usually “ground”.

Power is fed to the fuse...

Through circuit 295 and connector C172.. The male side of the connector is C172M, while the femaile side is C172F.

Let’s start by tracing power from hot to ground...

Okay, let’s stop right here. Where is Connector C172? How do you find it?

Most wiring books have a location view like this.

Using the numbers and letters, find C172 at A 6

Notice that C172F is on the left and C172M is on the right… These are mating connectors.

Find circuit 295. What is the pin number? What color is the wire? Write down both pieces of information.

Locate the wire where it passes through a connector

Now we not only know where C172 is...

…we also know what the connector pinout looks like, AND... …we know which pin is number 34 on the connector

There are three things we should notice about this current path. #1: The truck could have either of two switches, depending on whether it is equipped with a manual or automatic transmission. This is drawn as an “alternate current path.”

#2: the wires going into and out of the switch in question both pass through connector C172. #3: After the circuit passes through the switch, the circuit number changes from 295 to 140.

Find circuit number 140. What is the pin number? Write it down.

We know now that pins 34 and 32 are both part of the backup lamp circuit and that either pin could be the cause of a problem.

With that in mind, we inspect all four pins, i.e., the MALE and FEMALE pins 34 and 32. Finding no problem, we move on...

Now the circuit passes through a splice and two more connectors. The splice could be a problem, but it is usually taped into the harness and can be difficult to locate. It should be examined last.

Let’s find connector C148 in our location drawing:

Find D10 on the grid and locate connector C148.

This pinout legend is slightly different. Find circuit 140 and double check the wire color to make sure we’re still on track… Write down the pin number. Once again, we can find the connector on the vehicle, then locate the pin in that connector so that we can check the integrity of the circuit at the connector.

Now let’s go on to find C411 the same way...

Find F7 on the grid and locate connector C411.

The circuit number we’re looking for is still 140. Find it and write down the pin number. Once again, we can go to this connector, find the pin in question, and check the circuit.

Our last inline connector is C 403. Let’s find it on the vehicle like we did the others.

Find E10 on the grid and locate connector C403.

The circuit number we’re looking for is still 140. Find it and write down the pin number. Once again, we can go to this connector, find the pin in question, and check the circuit. By this time we should have a pretty good idea where the problem is, if we haven’t already found it.

One more potential problem point is the ground, namely G104. Let’s locate it.

Find E10 on the grid and locate connector G104.

…but on the schematic the ground looks very close to the lamps. Distance is not indicated on a schematic… Notice that the ground for the backup lamps is at the opposite end of the vehicle from the lamps…