Electrical Theory
THE KEY TO UNDERSTANDING ELECTRICITY, ELECTRICAL CIRCUITS AND TO INTELLIGENT TROUBLESHOOTING IS A THOROUGH KNOWLEDGE OF ELECTRICAL FUNDAMENTALS. THE FOLLOWING INFORMATION IS DESIGNED TO REVIEW THESE FUNDAMENTALS.ELECTRICITY
Electricity is an invisible force which behaves according to definite rules and produces predictable results and effects. Although we have learned to produce, store, use and measure electricity, no one knows just what electricity is. In recent years, scientists have developed the Electron Theory to explain the nature of electricity. It explains more thoroughly than any other theory, the behavior of electricity and magnetism.
ELECTRON THEORY FUNDAMENTALS
1. Everything consists of matter.
2. Matter is made up of molecules.
3. A molecule is made up of 2 or more atoms.
4. Atoms contain protons, neutrons, and electrons.
The nucleus of an atom has a positive electrical charge (+). An orbiting electron has a negative electrical charge (-). An electrically balanced atom has an equal number of positively charged protons in the nucleus and negatively charged orbiting electrons.
All atoms except hydrogen have a third component called a neutron. The neutron is a neutral particle, neither positive nor negative. Neutrons are clustered at the center with the protons but do not affect the balance of charges of the atom.
BOUND AND FREE ELECTRONS
The electrons in an atom revolve in one or more orbits around the core. The number of electrons in the outer orbit affects the ability of the atom to combine with other atoms and its ability to conduct electricity. Atoms tend to complete their outer rings; that is, to acquire as many electrons in the outer ring as possible. Although an atom can not have more electrons than it has protons, it can share electrons in its outer ring with other atoms. This is how atoms join themselves together to form molecules. Electrons in the inner orbits of an atom are closer to the positively charged nucleus and are strongly attached to it. These electrons are called bound electrons. Electrons in the outer orbit are farther from the nucleus and less strongly attracted. These are called free electrons.
ELECTRON FLOW
When atoms share electrons with one another, the positive and negative charges of each atom become unbalanced. As an electron moves from the outer ring of one atom into the outer ring of another atom, the first atom becomes positively charged because the protons momentarily outnumber the electrons. The protons instantly seek to attract another electron from another atom to rebalance the charge. This unbalancing and rebalancing of charges takes place very quickly (less than a microsecond), and the movement of free electrons from one atom to another is called electron flow, or electric current flow. This does not mean that any single electron travels the full length of a conductor. Instead, free electrons move from atom to atom and this movement results in the transmission of an electrical impulse from one end of a conductor to the other.
CONVENTIONAL THEORY OF CURRENT FLOW VS. ELECTRON THEORY
The Electron Theory states that current flows from "-" to "+". However, in automotive electrical systems we use the Conventional Theory of Current Flow: Current flows from the "+" terminal of the battery through the circuit and back to the "-" terminal of the battery. The Conventional Theory works well for automotive usage because modern automobiles ground the battery terminal.
MAGNETISM FUNDAMENTALS
BAR MAGNET
HORSESHOE MAGNET
The phenomenon of magnetism greatly expands the usefulness of electricity. Without magnetism, we could not have motors, generators, relays and solenoids, transformers and coils. Like electricity, we do not know exactly what magnetism is, but we do know how it reacts, what it does, and therefore how we can put it to use.
All magnets have a magnetic field, which is evidenced by lines of force, or magnetic flux, around the magnet. The strength of the magnetic field varies. It is strongest close to the magnet and gets progressively weaker away from it.
The area or extent of the magnetic field can be determined by means of a compass, which also shows the direction of the lines of force. Note: the lines of force leave the north pole of the magnets and re enter at the south pole; that the lines of force exerted by the horseshoe magnet are more concentrated between the two poles of the magnet.
TWO COMMON TYPES OF MAGNETS
Permanent: Permanent magnets are made from materials such as hardened steel that will become magnetic when subjected to an outside magnetizing force and that will remain magnetic even after the outside force is removed.
Temporary: Temporary magnets are made from materials such as soft iron that will remain magnetic only as long as an outside magnetizing force is present. When the magnetizing force is removed, the material returns to its nonmagnetic state.
NOTE: Electron flow creates a proportional magnetic flux around the conductor. Inductive electrical test pickups measure this magnetic flux that is proportional to current flow and convert this signal to an electrical reading.
ELECTROMAGNETS
Most temporary magnetic fields are produced by electricity flow. Whenever current flows through a conductor, magnetic lines of force develop around the conductor. This field forms a circular pattern; it can be visualized as a magnetic cylinder extending the full length of the wire. The strength of this field (the concentration of the lines of force) depends upon the amount of current flowing through the conductor. The greater the current flow, the stronger the field. This is the field produced by electromagnetism.
As mentioned, the magnetic field surrounds the conductor, which is carrying an electrical current. If this conductor is formed into a loop, the lines of force on the outside of the loops spread out into space; lines on the inside of the loop are confined and crowded together. This increases the density of lines of force in that area, and a much greater magnetic effect is produced with the same amount of current flowing.
In this illustration, one side of the loop will be a north pole and the other side will be a south pole. By increasing the number of loops, the magnetic field will be greatly increased. By winding the loops or coils on a core of soft iron, the field is further intensified.
RIGHT HAND RULE
The direction of the magnetic field can be determined by using the RIGHT HAND RULE. If you place your right hand over the conductor with your thumb pointing in the direction of current flow (from "+' to "-," or towards "-"), your curled fingers will show the direction of the magnetic field and the lines of force.
NOTE: For the Electron Theory, where current flows from negative (-) to positive (+), this is also known as the LEFT HAND RULE.
ELECTROMAGNETIC INDUCTION
The process by which a magnetic field causes current to flow in a conductor is a process that can be reversed. Under proper conditions, a magnetic field can cause current to flow in a conductor. This is called inducing or generating electricity by magnetism.
To induce voltage in a conductor, it is necessary to have relative motion between the conductor and the magnetic field, either by:
1. A magnetic field moving across a stationary field, as in an AC generator (Alternator).
2. A magnetic field building or collapsing across a stationary conductor, as in an ignition coil.
DC (DIRECT CURRENT) VS. AC (ALTERNATING CURRENT)
Electron flow in DC (direct current) moves in one direction only. Since we adhere to the Conventional Electrical Theory in automotives, DC current flow is from positive (+) to negative (-). The battery is a good example of a source of DC voltage. DC voltage does not have to remain absolutely constant and it's value can change.
When automobiles had relatively simple low power electrical systems, DC voltage produced by generators provided an adequate current supply.
AC (alternating current) is electricity that changes its direction at regular definite time intervals or frequency. This AC current changes its direction according to the Law of Sines. As shown in the graph, the current first increases to its peak, then decreases through zero. It changes its direction, increasing to its peak, then decreasing back through zero. This process continues to form a frequency or Sine Wave. The unit of frequency we use to measure the speed at which the current changes direction is called Hertz (Hz). In automobiles, AC current is produced by AC generators (Alternators) and, through the use of diodes, is changed to DC.
NOTE: AC current produced by sensors, i.e. TDC and ABS Speed Sensors, is not rectified to DC current. These are the only AC current signals found in LAND ROVER electrical systems.
AC voltage has found an increasing number of uses in automobiles in the past several years. AC generators (Alternators) were first introduced when increasing power demands and changing traffic and climate conditions proved too great for the DC generator. The AC generator (Alternator) produces alternating current which must be changed to direct current before it can be utilized by the vehicle's electrical system. This is accomplished by the use of a diode pack consisting of three positive and three negative diodes, called a Rectifier. Since diodes allow current to flow through them in one direction only, the resultant output is direct current (DC).
However, in recent years we have begun using AC voltage in its non-rectified (alternating) form. For example, we utilize the properties of AC as an on-off switch for the ignition coil in electronic ignition systems, as generated by the pickup coil in the distributor. In addition, RPM sensors like those used on the Engine Management System (EMS), and wheel speed sensors on ABS braking systems, also generate AC voltage.
The flow and behavior of electricity can easily be explained by comparing it to the flow of water through a pipe.
VOLTAGE IS PRESSURE
A storage battery and a water tower are similar, they both provide pressure. The battery is a source of electrical pressure and the water tower supplies water pressure. In other words, voltage is simply electrical pressure. And, it's voltage that pushes electricity through the wires in a circuit just as pressure pushes water through the pipes in a plumbing system.
Voltage is represented by the symbol B for electromotive force.
AMPERAGE IS FLOW
The flow of electricity and water can also be compared. An electric current is the movement or flow of electricity through a circuit just as water flow is the movement of water through a pipe.
Amperage is the electrical unit that tells you how much current is flowing through the wires of a circuit. Just as gallons-per-minute is the measure of the rate of water flow, amperage is the measure of rate of current flow. When a current of one ampere is flowing through a wire it means that a definite amount of current flow is present in the circuit.
Amperes are abbreviated as "amps," and are represented by the symbol I for intensity.
OHMS MEASURE RESISTANCE
Electrical resistance is the resistance to the flow of an electrical current. For example, a small wire offers more resistance to the flow of electricity than a large wire of the same material. In much the same way, a small pipe in a water system offers more resistance to the flow of water than a large pipe.
The symbol for resistance is R, and the Greek letter ohm (omega) is used as a symbol for ohm.
OHM'S LAW
The key to understanding electrical circuits and to intelligent troubleshooting is a thorough knowledge of electrical fundamentals. The heart of these fundamentals is Ohm's Law, which is the mathematical relationship between voltage, amperage and resistance.
Ohm's Law states that current flowing in a circuit varies directly with the voltage and inversely with the resistance. In other words, the pressure of one volt applied to one ohm of resistance will cause one ampere of current to flow. If voltage increases, current will increase; if resistance increases, current will decrease. If any two of the three factors (volts, amps, ohms) are known, the missing one can be found by applying Ohm's Law. The mathematical equation is:
WATTS
The watt is the unit of measurement that indicates the electrical power in a circuit. To calculate watts, simply multiply the current (in amperes) by the voltage. The mathematical equation is:
