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| Basic Electronics A knowlegde of at least basic electronic principles is essential to diagnosing and repairing today's modern computer-controlled vehicles, and has been important since the invention of the internal combustion engine, as gasoline/ethanol engines use electric spark to ignite fuel in the engine. The relationships, equations and other facts shown here are intended to give a general understanding of electronics. Electronics engineers use much more complicated versions of these equations which take into account any number of variables that can affect an electrical circuit, and use additional units to measure more complex electrical properties. The information in this article is designed to give drivers and others a basic idea of how electronics work, and should not be used to diagnose, repair, or construct any electrical device, automotive or otherwise. Please remember that severe damage or injury, even death, could result from improper repair or modification of any automotive system, including electronic systems.
Electrical Theory Electricity is the flow of electrons. An electron is a negatively charged subatomic particle which moves at the speed of light. When there is no electrical flow, electrons orbit the nucleus of the atom, which is composed of protons, a positively charged subatomic particle, and neutrons, which have no positive or negative charge, and essentially provide a stabilizing ballast for the atom. When an atom has more electrons than protons, it has a negative charge. When an atom has fewer electrons than protons, it has a positive charge. Positively or negatively charged atoms are known as ions. When a circuit has more positive ions at one end and more negative ions at the other, it is said to have electrical potential (see Volts below). If there is enough potential to overcome any impedence in the circuit (see Ohms below), electrons will flow. The higher the potential and the lower the impedence, the more electrons will flow from the negatively charged end to the positively charged end (see Amps below). The former negative ions become neutral as they lose their extra electrons, and the positive ions become neutral as they gain their missing electrons back from the negative ions. Charging a battery, for practical purposes, removes electrons from the neutral atoms on the positive side, and delivers them to the neutral atoms on the negative side, restoring them to a positive- and negative-ion state.
Measuring Electricity The following are common units of measurement for electrical potential, flow, resistance, power, work, electrical charge, and capacitance as well as equations that relate these different values. Understanding these principles and relationships is essential to understanding electronics. Volts (V) Volts are a measure of electrical potential, or to put it another way, electrical pressure, and often referred to as charge when it applies to a battery's stored potential. Similar to the pressure in a water pipe, voltage is what forces electricity flow. Voltage is created when there is a negative charge in one area, and a positive charge in another area, such as in the positive and negative sides of an automotive battery. When a circuit is closed, meaning a connection between the positive and negative areas is made, electricity flows. A higher voltage is able to flow electricity through a circuit with a higher resistance, just as a leaking water pipe may not drip with no pressure, and yet spray water out when water pressure is present. Similarly, extremely high voltage between a thunder cloud and the ground is able to overcome the extremely high resistance of the air between them, resulting in a very large electric spark, known as lightning. The more voltage at a given resistance, the more electricity will flow. Ohms (Ω) Ohms are a measure of electrical impedence, or resistance. Similar to a closed valve on a water faucet, a high electrical resistance may prevent electricity from flowing. The lower the resistance, the more electricity will flow at a given voltage, similar to gradually opening a water faucet. Amperes (A) Amperes, or amps, are a measure of electrical flow, similar to measuring Gallons Per Minute through a water pipe. The higher the voltage and lower the resistance in a circuit, the higher the amperage, just as higher water pressure and opening a faucet further will cause more water to flow from the faucet. Ohm's Law As you can see, volts, ohms and amps are related. Knowing this relationship, any one of these values can be calculated if the other two are known. This relationship is known as Ohm's Law, and is reflected in this equation: amps=volts/ohms. Therefore, the following equations are true: volts=amps x ohms ohms=volts/amps. If an automotive battery has a charge of 12 volts, and a closed circuit has a resistance of 3 ohms, the electrical flow through the circuit will be 4 amps. Watts (w) Watts are a unit of power. A unit of power you may be more familiar with is horsepower(hp). A watt and a horsepower are two units which measure exactly the same thing, just as a foot and a mile are both measurements of distance. For practical purposes, 1 horsepower is equal to approximately 746 watts. Watts are more commonly used in measuring electrical power because they are directly related to volts and amps. This relationship is reflected in this equation: watts=volts x amps Therefore, the following equations are true: volts=watts/amps amps=watts/volts If an automotive charging system is supplying a constant 14 volts to a circuit, and there are 10 amps flowing through the circuit, the circuit is using 140 watts. Joules (j) and Kilowatt-Hours (kwh) Joules are a unit of work done. A unit of work you may be more familiar with is the kilowatt-hour, which is the unit of electricity your power company bills you for. A kilowatt-hour (kWh) is equal to using 1,000 watts for one hour. So a single 100 watt bulbs, at its rated voltage, would use 1 kilowatt-hour every 10 hours. A joule is equal to 1 watt-second, or 1 watt being used for 1 second. Since there are 3600 seconds in an hour, and 1,000 watts in a kilowatt, 1 kilowatt-hour is equal to 3,600,000 joules, or 3.6 megajoules (MJ). Here are the equations: joules=watts x seconds kilowatt-hours=[(watts x seconds)/3600]/1000 or to simplify, kilowatt-hours=kilowatts x hours Therefore, the following equations are true: watts=joules/seconds seconds=joules/watts
Coulombs (c)
Coulombs are a measure of electrical charge. One coulomb is equal to the amount of electrical charge moved through a circuit with a current of 1 amp in 1 second. Think back to my earlier comparison of amps to gallons per minute. If 1 amp were equal to 1 GPM, then 60 coulombs would be equal to 1 gallon. A coulomb can be thought of as a quantity of electrons, while an amp is the flow of 1 coulomb of electrons through a circuit every second. Here are the equations:
coulombs=amps x seconds
Therefore, the following equations are true:
amps=coulombs/seconds
seconds=coulombs/amps
Farads (f)
Farads are a measure of capacitance, or the storage capability of a capacitor, see below. One farad is equivalent to the amount of capacitance for which 1 volt causes a charge of 1 coulomb. So if 1 volt is applied to a capacitor with a capacitance of 1 farad, the capacitor would store up to 1 coulomb of electrical charge. Since 1 amp is equal to 1 coulomb per second, a 1 farad capacitor with 1 volt of electrical potential would take 1 second to completely discharge the 1 coulomb of electrical charge stored within it, if the current flowing from the capacitor was 1 amp. Here are the equations:
farads=coulombs/volts or,
farads=(amps x seconds)/volts
Therefore, the following equations are true:
coulombs=farads x volts
volts=coulombs/farads
Electromagnetic Energy
Electromagnetic energy moves through space, the atmosphere, and in some cases through solid objects in a wave pattern, at over 670 million miles per hour. Different types of energy produce different wavelengths. Electromagnetic energy which produces a wavelength detectable by the human eye is known as visible light. Other forms of electromagnet waves include radio signals, X-rays, microwaves, infrared and ultraviolet light, among others. Many electrical devices are designed to produce or absorb electromagnetic energy, so it is important to have a basic understanding of electromagnetic waves.
Electrical Components
Batteries Batteries are an electrical storage device that convert chemical energy to electrical energy. Automotive batteries are a rechargeable wet-cell type battery, which use liquid acid, minerals, and lead plates to store electrical power. The acid produces a chemical reaction, which produces an electrical voltage. Similar to burning a tank of fuel, as the battery is used and the electrons flow from negative to positive, eventually the chemical reaction uses all of the battery acid and turns it into a different chemical which can no longer react to produce voltage. Applying a charge to the battery pulls electrons back out of the positive side of the battery and into the negative side, and essentially reverses this chemical reaction, restoring the battery acid to its original state, in which it can once again react and produce an electrical voltage. Conductors and Insulators A conductor is anything that can flow electricity, while an insulator is anything with an extremely high resistance to electrical flow. The most common type of conductor used in electronics applications is copper wire. Copper is chosen because of its very low resistance and relatively low cost. Many other metals such as gold, platinum and iridium are used sparingly in automotive and other electronics, since they provide significantly lower resistance to electrical flow and can withstand environmental conditions such as high heat, but at a significantly higher cost. Almost anything can technically be a conductor, such as air, which conducts electricity which we see as lightning and other electric sparks, such as the spark that jumps the gap of an automotive spark plug. Many other materials generally referred to as insulators may conduct electricity if enough voltage is present. Plastics are commonly used as insulation on wire. Ceramics are another common insulator, and are used in automotive spark plugs due to their ability to withstand high temperatures and insulate against the very high voltage required to produce a quality ignition spark.
Coils
Coils are an electrical device usually consisting of a piece of iron surrounded by a conductor, usually a very small wire. This wire may be wound directly on the iron, or may be wound on another material to allow the iron piece to be movable, such as in a solenoid, see below. Coils produce a magnetic field when energized. This field may be used to magnetize the iron, in which case it is called an electromagnet. Electromagnets are used in automotive relays, see below.
In some cases, coils may be surrounded by iron rather than wrapped around it. Electric motors work by energizing a series of electrical coils supported on a center shaft. This assembly is known as an armature. The electromagnetic field produced by these coils attracts or repels them to iron pieces which surround the armature. This attraction or repulsion normally causes the armature to spin, although there are instances where an armature is fixed and the outer housing spins. Automotive starter motors are an example of an electric motor.
Coils are also used in audio speakers. The coil in a speaker is placed next to a magnet. The audio signal is passed through the coil, causing it to push and pull it self to and from the magnet. The coil is attached to a diaphragm, which vibrates as it is pushed and pulled by the coil, producing sound waves.
Coils can also be used to produce electricity by simply passing a magnet through or near them. This is the principle behind automotive alternators and wheel speed sensors. A microphone is basically the same as a speaker, except that the diaphragm is vibrated by sound waves, and the attached coil then vibrates in the magnetic field of the magnet, thereby producing an electrical current in the coil in the form of an audio signal.
The magnetic field produced by an energized coil can also be used to produce an electrical potential in another coil. Using coils with different numbers of "turns", or numbers of wraps of the wire around the iron, can step-up or step-down the voltage. This type of device is known as a transformer. Since a transformer doesn't generate electricity, it is bound to Ohm's Law, see above. As it steps up voltage, amperage is reduced. An automotive ignition coil is an example of a transformer.
Switches and Relays
An electrical switch is a device which "opens" and"closes" an electrical circuit. Switches can be controlled by the user, or by some automated device. Often times, the switch used is not capable of handling the current used by the device it operates. For example, an automotive ignition switch is not capable of handling the very high current required to turn a starter motor. A relay uses a small current, controlled by a switch of some sort, to close a much larger switch inside the relay. This larger switch is usually operated by an electromagnetic coil inside the relay, which pulls the switch closed when the "signal" voltage is switched on. Relays can also be normally-closed, meaning the "signal" voltage turns the relay off. Some relays switch between 2 different circuits depending on the presence of the "signal" voltage.
Solenoids
Solenoids consist of an electrical coil that, when energized by an electrical potential, produces a magnetic field, and a metal cylinder which is pulled or pushed in a straight line by the magnetic field. Most solenoids use a return spring to return the cylinder to its original position when the coil is de-energized. The metal cylinder in a solenoid may be attached to a valve or a switch, such as a fuel shutoff solenoid on a diesel injection pump, which attaches to a shutoff valve. Some solenoid cylinders may themselves be valves, such as automatic transmission shift solenoids, which control flow of transmission fluid. Other solenoids may be parts of a special type of relay, with the cylinder itself acting as a switch, such as in automotive starter solenoids.
Semiconductor Components
A semiconductor has properties which allow its resistance to electrical flow to be altered under certain conditions. Silicon is a common semiconductor, used in automotive Control Modules, sensors and millions of other electronic devices. The two most common electrical components to utilize semiconductors are diodes and transistors. A diode is basically an electrical one-way valve, while a transistor has a similar function as a relay, but has no moving parts and can be made extremely small- for example, there can be millions of transistors in a computer chip smaller and thinner than a dime. A diode has a positive and negative end, and when electrical potential is reversed, the diode prevents electrical flow. A light-emitting diode (LED) is a special type of diode which converts electrical energy directly into light. This makes them far more efficient and reliable than incandescent light bulbs, which use electricity to heat a filament, which causes it to glow, and more efficient than fluorescent and neon bulbs, which use electricity to excite a gas inside the bulb, which then emits light.
A transistor has 3 terminals, with one terminal controlling the on/off function of the transistor. When an electrical voltage is applied to this terminal, resistance is effectively reduced across the other two terminals, allowing electricity to flow. Some transistors effectively vary the resistance across these terminals depending on the voltage applied to the "switching" terminal. These are called field-effect transistors (FET's), and are used to amplify electrical signals, such as the audio signal from a car stereo.
Photovoltaic Devices
A photovoltaic device is a special type of semiconductor component which produces an electrical voltage when illuminated. Think of it as an LED in reverse. While an LED converts electricity into light, a photovoltaic device converts light into electricity. Solar cells used on some hybrid vehicles are an example of a photovoltaic device. Automatic headlight sensors are sometimes confused as solar cells, but are actually light-dependent resistors, see below.
Resistors
Resistors, as the name implies, provide resistance in a circuit. Resistors come in various types, and can have a fixed or variable resistance. Most variable resistors are operated manually or mechanically. These are called either rheostats if they have 2 terminals or potentiometers if they have 3 terminals. Rheostats are intended to vary the amount of electrical current allowed to flow through a circuit, while potentiometers vary the voltage in a circuit. A common example of a potentiometer is a radio volume control knob.
Another type of variable resistor is a thermistor, which varies its resistance based on temperature. Automotive air intake temperature sensors are a common example of a thermistor.
A light dependent resistor varies its resistance depending on the amount of light illuminating it. LDR's are usually used as light/dark detectors, such as the automatic headlight sensor on modern vehicles, or automatic night lights in your home.
Transdeucers
Transdeucers normally consist of a rheostat with an attached diaphragm. Transdeucers of this type are used to convert hydraulic or pneumatic pressure into an electrical signal. Pressure on one side of the diaphragm moves the diaphragm against a reutrn sring, which moves the rheostat. They are used to provide an electrical signal which corresponds to a specific pressure, such as automotive oil pressure sending units, which can operate an oil pressure gauge or send information to a control module. This differs from an automotive oil pressure switch, which uses an on/off switch attached to a diaphram, and can be used to turn off oil warning lights and turn on electric fuel pumps as soon as oil pressure is present. Capacitors
Capacitors, like batteries, are a type of electrical storage device. Unlike batteries, capacitors are a short-term storage device, which normally discharge rapidly when electrical potential is removed from them. Capacitors use no chemicals to store or produce electrical potential, but rather have plates, separated by a special type of insulator called a dielectric, on which a positive and negative charge is stored. Capacitors are used for a variety of purposes in electronic circuits, such as those found in automotive control modules. If you've ever used an old radio and noticed that it "fades" after the switch has been turned off, this is a result of electrical potential discharging from capacitors, which continues to power the radiofor a second or two when the outside power source is removed by the power switch.
Fuses and Circuit Breakers
Fuses are a device designed to protect an electrical circuit from damage. Fuses accomplish this by being the weak point in a circuit. By failing at a preset amperage, a fuse opens the circuit, thereby disabling it. Excessive current can damage wiring and other circuits, normally due to excessive heat. This excessive heat can also pose a fire hazard. Fuses are made of a glass or plastic housing, containing a small conductive link which is easily damaged by a certain amount of current, which can vary greatly. The current at which the fuse is designed to fail is normally displayed on the fuse housing in amps. Circuit breakers perform a similar function to fuses, but are resettable. Circuit breakers generally use a spring-loaded set of contacts, which when heated to a certain temperature by the electrical current, warp, causing them to disconnect. Most automotive circuit breakers reset automatically when they cool down, while other circuit breakers have to be manually reset.
Antennas
Antennas are electrical devices capable of transmitting or receiving radio signals. A receiver antenna absorbs the invisible electromagnetic energy which fills the entire universe, producing an electrical current in the antenna and attached circuit. Depending upon the exact length of the antenna, it will be better at absorbing electromagnetic energy of a certain wavelength. If you have ever used an old radio, and gained better reception on a particular station by extending or retracting the telescoping antenna, you have seen this principle in action. Additionally, they work better when they are oriented at a right angle to the incoming signal, which is why antennas usually perform best when positioned vertically for local radio stations. As the entire universe is filled with a large amount of electromagnetic "noise", radios must be designed to filter this noise. You can hear this "noise" by tuning a radio to a frequency which is not used by any radio stations within broadcast range. You can even pick up the electromagnetic noise generated by global lightning strikes on certain frequencies.
Transmitter antennas produce the invisible electromagnetic energy that radio signals consist of. This is accomplished by applying an electrical audio signal to the antenna, and modulating, or varying at a constant rate, either the frequency or amplitude (strength) of the signal. These two methods of broadcasting are more commonly known as FM and AM radio.
Summary
As you can see, modern vehicles depend on electronics, and understanding how these electronics work is vital in understanding how a vehicle and its accessories operate. For detailed information on these systems, and the science behind electronics and other automotive principles, check out other Tech Info articles.
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