ELECTRICITY

SYMBOLS We have looked at several different symbols We will be using many of them from now on so get used to them

Conductors Materials that allow electricity to flow easily thru it –Material made up of atoms with the valance ring (outer) with 1, 2, or 3 electrons Most metals

Insulators Materials that don’t’ allow electricity to flow easily thru it –Material made up of atoms with the valance ring with 5, 6, 7, or 8 electrons Air Glass Paper Wood

Semi Conductors Materials that are not good conductors or good insulators –Material made up of atoms with the valance ring with 4 electrons Carbon (C) Silicon (Si)

Electricity The flow of electrons –How do we get electrons to flow? Electrons being held In orbit by the attraction Of the protons

Two copper atoms side by side

Copper wire Made up of billions of copper atoms Electrons bouncing around in random drift in the wire Remember the wire is full of electrons at Random drift.

Atoms loosing or gaining electrons All atoms have an equal number of protons and electrons When an atom looses one electron it becomes a Positive Ion –It is now unstable and wants an electron back to become stable When an atom gains an electron it becomes a Negative Ion –It is now unstable and wants to get rid of an electron to become stable

Extra Electrons here Shortage of electrons here Now the electrons that were at random drift are in a directed drift

Voltage Electrical pressure (pushes current) Atoms that are short electrons and atoms with extra electrons Measured with a voltmeter Unit of measure is the volt Note! A good voltmeter won’t have any flow thru it

Ways to make voltage Magnets Chemical Pressure Heat Light Friction Most common

Current The directed movement of electrons or the flow. (pushed by voltage) Unit of measure is the amp or ampere Measured with an ammeter or amp meter

How much is one amp? One amp is 6.25 X 10 to the 18 th power of electrons past a given point per second. (one Coulomb) 6,250,000,000,000,000,000

Conventional theory Says that current flows from + to - Scientists first guessed that it was the proton that was in motion in the atom

Electron theory Says that current flows from – to + When scientists discovered that it was the electron that was in motion, electron theory was born

Does it matter? When talking about electronics, it does matter which way current flows, but for basic electricity, it doesn’t Most automotive texts, and classes still teach conventional theory, so that is what we will stick with.

Resistance Opposition to current flow (anything that slows down current) Unit of measure is the ohm Measured with an ohmmeter

Factors that affect the resistance of a circuit Type of material used –Conductor / Insulator / Semi-conductor Length of the circuit Diameter of the circuit Temperature Connections

Wire diameter AWG Gauge size American Wire Gauge Metric –Millimeters squared

Elements of a Circuit (must have) Nice to have

One wire circuits

OHM’S LAW When the voltage and resistance are equal in a circuit, ONE amp will flow (Saunders version) One volt will push one amp through one ohm of resistance A picture is worth a thousand words

Ohms Law Current flow is strictly a result of how much voltage and resistance there is –To get more current Increase voltage Decrease resistance Or both –To get less current to flow Decrease voltage Increase resistance Or both

Ohm’s law formulas Voltage is represented by the letter “E” Amperage is represented by “I” Resistance is represented by “R” E = I x R

Here is an easier way to remember The three formulas Need to know

When you know the amperage and resistance of a circuit you can figure the voltage Voltage = amperage times resistance

When you know the voltage and amperage of a circuit you can figure the resistance Resistance = voltage divided by amperage

When you know the voltage and resistance of a circuit you can figure the amperage Amperage = voltage divided by resistance

D.C Challenge Let’s apply what we have learned –Ohms law We will also learn about electrical power or watts –Power is the rate of doing _________ –Watts are the amount of electrical work There will be an ohm’s law and power quiz after D.C. Challenge

ELECTRICITY After ATECH 1-7

Series Circuit Rules Only one path Amperage stays the same Each resistance adds up to the total R1+R2=Rt Voltage divided between the loads (all used up or dropped) Must know!

Voltmeters Hooked across or in parallel –Red to most positive and black to most negative –Used in a live circuit

Ammeters Hooked in series (in line and part of the circuit) –Red to most positive and black to most negative –Used in a live circuit Be careful not to hook across voltage (it will blow fuse

Ohm Meters Used in a dead circuit Must be hooked across or in parallel Analog meter must be calibrated to compensate for battery Part you want to measure must be isolated from the rest of the circuit Good connections

Type of circuits Atech 1-7 Atech 8-11 Atech 12-14

ATECH 7-11 Parallel circuits –The rules are going to change

Lets go get it done!

ELECTRICITY

Problem Circuits

Open Circuit No flow Infinite resistance Won’t use circuit protection Meters to find open –Volt (will read source voltage across open) –Ohm (will read infinite across open)

High resistance Less flow than normal Won’t use circuit protection Meters to find –Voltmeter (will drop more voltage at problem) –Ohmmeter (will read more resistance at problem)

Short circuit More flow than normal May use circuit protection Meters to use –Ohmmeter (less resistance at problem) –Voltmeter (only if circuit is still live, voltmeter will read less voltage drop at problem)

Grounded circuit (short to ground, dead short) Huge flow (no resistance) Will use circuit protection or burn up circuit Ohmmeter is the only meter to use (circuit will be dead) –Ohmmeter will show no resistance to ground at the problem

Short to voltage Hardest to find and fix When one circuit shorts voltage into another

Low voltage Won’t use circuit protection Less amps will flow Caused by –Bad battery –Charging system fault

Circuit Protection

D.C. Current Current always flowing the same way

A.C. Current Current flows first one way, then the other

Type of circuits