Chapter 7 - Electrical System Fundamentals
 
 

Electron Theory

                Atomic Structure

                    Nucleus
                        Protons
                        Neutrons

                   Electrons
                        Free electrons
                        Bound electrons

Electrical Circuits

            3 Elements of a circuit

                        Source
                        Conductor
                        Load

            Complete Circuit


 
 


            Open Circuit - The conductor is missing - no electrons will flow.


 
 


            Short Circuit - The load is missing - uncontrolled electron flow results in damage to the conductor or source.


 
 



                Sources

                        Mechanical

                            Generator
                            Piezo-electric

                        Heat

                            Thermocouple

                        Light

                            Solar cell

                        Chemical

                            Battery

                Conductors - free electrons

                            copper
                            aluminum
                            steel

                        Non-conductors (insulators) - bound electrons

                            plastic
                            rubber
                            glass

                Loads

                        Mechanical

                        - starter motors

                        Heat

                        - defroster grids; heated windshields; block heaters

                        Light

                        - vehicle lighting systems

                        Chemical

                        - battery charging
 
 

Electrical Terms

            Electromotive Force (EMF) - is a measurement of electrical potential, or the amount of
                    electrical "pressure" available to force electrons through a circuit. It is measured in
                    VOLTS. Abbreviation is V, symbol is E.

            Current - is a measurement of the rate of flow of electrons (how many electrons pass
                    any point in a circuit in a certain amount of time). It is measured in AMPERES
                    [or AMPS]. Abbreviation is A, symbol is I.

            Resistance - is a measurement the amount that any device will attempt to restrict electron
                    flow. It is measured in OHMS. Abbreviation is the Greek letter Omega, symbol is R.

            Power - is the rate at which electrical energy is converted to some other form. It is
                    measured in WATTS. Abbreviation is W, symbol is P.
 
 

Ohm's Law

E = I X R

Electromotive Force = Current X Resistance

Volts = Amps X Ohms





Watt's Law
 
 

P = I X E

Power = Current X Electromotive Force

Watts = Amps X Volts


                Using Ohm's Law and Watt's Law
 


 



                        Ohm's Law - the voltage (E) is known and the resistance (R) is
                                known. The current flow can be calculated using I = E/R - or
                                I = 12 volts/6 ohms = 2 amps.

                        Watt's Law - the power (P) "consumed" in this circuit is found by
                                using P = I X E - or P = 2 amps X 12 volts = 24 watts.
 
 

Series Circuits


 


                                - One path for electron flow.
                                - An open in a series circuit will affect the entire circuit.
                                - A short in a series circuit will only affect the shorted load.
                                - As loads are added, total circuit resistance will increase.
                                - Current flow is the same at any point in the circuit because there
                                        is only one path to for it to follow.
                                - There is a voltage drop (or loss of "pressure") at each load depending
                                        on the resistance of the load.

Parallel Circuits
 

                                - There is more than one path for electron flow.
                                - An open in a parallel circuit will only affect that branch of the circuit.
                                - A short in a parallel circuit will affect the entire circuit.
                                - As loads are added, total circuit resistance will decrease because more
                                        electrons can now flow in the circuit because there are more paths.
                                - Current flow in each branch of the circuit will depend on the resistance - the
                                        most current will flow through the least resistance. Total circuit current is
                                        found by adding the currents flowing through each branch.
                                - The voltage is the same, and equal to source voltage, at any point in the circuit.