Electricity is an area that many enthusiasts have trouble grasping when restoring or just maintaining their muscle machines; its characteristics are often shrouded in mystery. Electricity is an intangible and isn't as readily understood as a mechanical process can be. There are hordes of enthusiasts who will pick up a spray gun or torque wrench to work on their ride, but when it comes to the electrical system, they either ignore the problem and hope it goes away, or they sell the car outright and let someone else deal with it.
Hemmings Muscle Machines
is here to help. We've put together a two-part primer that should help a lot of you gain a working knowledge of your car's 12-volt electrical system. Part One focuses on the theory of electricity, and the second part offers hands-on diagnostic tips.
To the untrained eye, electricity sometimes doesn't respond as one would expect it to. Quite often, it does exactly the opposite of what would be assumed. If you remember anything from this primer, remember this: Electricity always takes the path of least resistance, and if it is doing something beyond your expectation, it is simply because that is the easiest route for it to take to ground.
With that established, let's get going and let the current flow!
Going With the Flow
There are three basic units of electricity: voltage, current, and resistance.
Voltage (or the pressure which electrons are under) is measured in volts. The symbols used for volts are "V" (volts) and "E" (EMF). Smaller voltages are measured in millivolts (1/1,000 of a volt) or even in microvolts (1/1,000,000 of a volt). Larger amounts are measured in kilovolts (1,000 volts) such as produced by the secondary ignition system.
Current (or how fast electrons move) is measured in amperes. The symbol for amperes is Amps, or in our diagrams "I." Smaller current flow is measured in milliampere (ma), which is 1/1,000 of an ampere. Microampere (ua) is 1/1,000,000 of an ampere.
Resistance (or how hard a conductor resists the flow) is measured in ohms. The symbol for ohms is the Greek symbol Omega (?), but in our diagrams, we'll use "R".
Let's start off by thinking of your car's electrical system as you would a simple plumbing system. Voltage would be the water pressure inside the pipes. Current would relate to the rate at which electricity flows through the pipes. Resistance is the size of the pipe itself.
All three of our basic measurements relate. The most basic electrical engineering equation says that current is equal to voltage divided by resistance, or I = V/r.
Think about our plumbing analogy again: You're watering your garden. What would happen if your water pressure increased? More water would come out of the hose. The same is true of an electrical system. By increasing voltage, you make more current flow.
What if you increased the diameter of your garden hose at the same time? That would also allow more water to flow. Therefore, by decreasing resistance, flow of electrons increases.
Electrical power is measured in watts. For any electrical system, power (P) is equal to the voltage multiplied by the current: P = VI.
Another liquid example: Aim the nozzle of your garden hose at a waterwheel. You can increase the speed at which that wheel turns two ways: Either increase the pressure coming out of the hose, or increase the flow rate of the water. In an electrical system, to increase the light coming from a 12-volt bulb, you can either increase the voltage, or increase the current.
Conductors, Insulators and In-Between
Current flow can only take place in a substance in which there are a great number of free electrons. Such substances are called conductors. Good examples of conductors are copper, gold and steel.
The opposite of a conductor is an insulator, in which it is difficult or impossible to cause current flow. These materials, such as rubber, wood, bakelite and porcelain, are said to have high anti-electric properties or dielectric strength.
In between insulator and conductors are materials in which it is difficult to produce a current. All conductors have a certain resistance or opposition to current flow. Resistance can be from composition of the material or its physical shape.
In electrical jargon, there are good insulators and good conductors, but in reality, there is a whole range of conductors, semi-conductors and insulators, each with its own particular use.
George S. Ohm, a scientist of the early 1800s, formulated a law that links the relationship of voltage, current and resistance in a basic circuit. He found that the current of a circuit is directly proportional to the applied voltage and inversely proportional to resistance in the circuit.
All you need to remember as an auto enthusiast is:
When resistance goes up or down, current flow goes up or down respectively, assuming the voltage is the same.
When voltage goes up or down, current flow goes up or down respectively, assuming the resistance stays the same.
When resistance goes up, current goes down, assuming voltage stays the same.
When resistance goes down, current goes up, assuming voltage stays the same.
Let's put this into practice in a car headlight system:
If the bulb is burned out, there is no completion of the circuit to ground from the power source, and the headlamp does not illuminate. There is no current flow through the circuit, and it is considered open.
If the headlamp is very dim, then we can deduce the resistance (opposition to electron flow) is high. This can be determined only after the system voltage is confirmed. If the voltage is normal and the bulb is dim, then the electron flow is being limited by high resistance on either the supply or ground connection.
This is in contrast to a flashlight going dim since, in that situation, the voltage supply is not staying constant as Ohm's laws states must happen for the equation to work.
If you were to take a headlamp bulb that was designed for a 6-volt application and install it in a 12-volt system, the bulb would burn out or fail prematurely. This substantiates the version of Ohm's law that states that if the voltage goes up and the resistance stays the same, the current flow will increase. The 6-volt bulb burned out because current flow (electron speed) from a higher operating voltage (electrical pressure) created excessive heat.
Your Battery and You
Electromotive force (EMF) is required to move electrons. EMF can be generated through friction, chemical reaction, light, pressure and magnetism. An excellent example of EMF is the wet-cell battery under the hood of your car.
In approximately 1800, Alessandro Volta found that two different metals (copper and zinc) separated by moist paper would produce current flow. His "voltaic cell" produced about 2.2 volts, and functioned by using a working fluid or electrolyte that took electrons from one of the metal electrodes and deposited them on the other one.
In the production of voltage, the voltaic cell destroys the two electrodes. It is an example of what is called a primary cell. It cannot be recharged after it is discharged (a common flashlight battery can be considered a primary cell). Each cell, no matter how large or small, will produce only 2.2 volts. To make use of the voltage, you must connect the positive and negative sides of the cell into a circuit that allows the electrons to return to the positive plate. That's why a 12-volt car battery has six cells.
To get more voltage, you must connect more cells together into what now becomes a battery, or several cells in series. The voltage available from two voltaic cells connected in series is double the voltage of one, or 4.4 volts. For this reason, an automotive charging system is usually designed to produce between 13.5 and 14.7 volts since a 12-volt battery will produce near 13.2 volts (6 X 2.2).
Cells can also be connected in parallel, which defines positive-to-positive and negative-to-negative. When connected in this manner, the voltage remains the same, but the capacity is increased. When jump-starting a car, the two vehicles are connected in parallel.
The proper name for an automotive power source is a "storage battery." It stores the EMF required to operate the vehicle's electrical components. In operation, it is roughly similar to a voltaic cell, except that it has the added ability to be recharged, or put back into its original charged condition. This type of battery is made of storage cells called secondary cells.
The storage cell is sometimes referred to as a lead-acid cell, because these two materials were a part of its construction for so many years.
The basic components of the automotive battery are:
positive plate (lead peroxide)
negative plate (sponge lead)
electrolyte (sulfuric acid and water)
When the two plates are submerged in the electrolyte (36% acid and 64% water), the cell develops an EMF or a voltage due to the chemical reaction. As the cell discharges, the plates become more and more the same, and the electrolyte becomes more and more plain water. Electrons are supplied to the negative plate to replace those being drawn off into the circuit as long as the plates are dissimilar and the electrolyte does not revert to water.
Discharging and recharging the cell over and over will eventually wear the components, since the chemical reversal is never 100 percent effective. Finally, the cell will reach a stage where the plates can't be made dissimilar through the application of an electric current. At this time, the battery will need to be discarded.
By the 1960s, the generator was replaced with a smaller unit that was called an alternator. Whereas in a generator, A.C. was changed to D.C. by mechanically connecting and disconnecting the conductors from the brushes, an alternator uses overlapping windings in a component called a stator, which still creates a pulsing direct current, but of a much smoother and continuous variety.
An alternator consists of a stationary set of windings called a stator. Most alternators have three sets of windings in the stator with each phase consisting of many conductors arranged around the inside of the alternator case. The rotor or turning magnet of the alternator is not a permanent magnet but a powerful group of electromagnets within a core, with a number of fingers that are north and south poles. The rotor turns at a much higher speed than was possible with a generator while still providing acceptable life.
To rectify or convert the A.C. into D.C., the alternator uses tiny semi-conductors called diodes. These can be thought of as one-way electrical check valves because they will pass current only in a single direction. Diodes are either positive or negative. The construction determines their polarity. These rectifiers are inserted into the internal circuitry of the alternator so the current will be allowed to flow from the alternator stator windings in a positive direction, but will be stopped if it tries to travel in a reverse direction.
Due to the additional stator windings, the speed of rotation and the multiple magnetic fields created by the rotor, the output of an alternator is smooth and continuous even at idle and low speeds.
If a conductor formed into a coil is brought near another conductor formed into a coil, and the first coil is connected to a current, the current induced in the second coil is much higher than in a straight conductor. The coil which carries the current into this type of induction system is called the primary winding of the coil. The coil into which the EMF is induced is called the secondary winding of the coil.
The amount of wire in both the primary and secondary windings, along with the primary voltage, controls how strong the induced EMF becomes. To those of you following along, this describes an ignition coil used on an internal combustion engine.
All automobiles made during the past 70 years incorporate an electric motor for starting the internal combustion engine. Most commonly referred to as a starter motor, the proper name for this device is a cranking motor.
When a conductor carrying an electric current is placed in a magnetic field, the field around the conductor and the magnetic field of the magnet interact with each other. The conductor will tend to move away from the combined field and toward the weakened field. That's because the magnetic fields tend to aid one another on one side of the conductor and oppose each other on the other. The conductor is pushed from one side and pulled from the other. This is the basic principle that makes an electric motor operate.
Motors behave with certain characteristics in an electric circuit. In operation under load, while connected to the mechanical component they are designed to power, they consume a certain amount of electrical current. Freed of this load, they consume less power, and when overloaded they use an excessive amount of current.
Electric motor circuits are equipped with a circuit protection device, usually a circuit breaker or fuse that opens the circuit when current flow exceeds safe limits. The only motor that does not have this feature is the starter motor, which is classified as an intermittently operating motor. A constant-duty motor large enough to safely turn the engine for long periods of time would be at least as large as the gasoline engine itself. For this reason, all of the parts in the cranking motor circuit are extra-heavy to handle the current draw associated with starting the engine. Contrast the size of a typical continuous-duty motor such as the heater blower motor with an intermittent-duty motor of about the same torque rating: the windshield washer pump motor. Obviously, the blower motor is much larger.
Other Important Facts
As we finish up Part One, there are a few important facts that need to be mentioned in anticipation of diagnosing an electrical problem in your ride. If the load is removed from a circuit and placed to ground, the full potential energy of the storage battery will be passed along this path. An example of this would be a sheetmetal screw piercing a wire. Many enthusiasts and professionals call this condition a "short circuit." That is not correct. Its proper name is an "unintentional ground."
In contrast, two circuits touching one another, which is referred to as "copper-to-copper," is a short circuit. A practical example of a short would be the interior light coming on when the driver blows the horn.
This may seem like arguing semantics to some, but it must be understood because the diagnostic procedure and test equipment used to find a short are completely different from those for an unintentional ground.
Other things to remember are that an ohm meter is always used in an unpowered (disconnected from its power source) circuit, an ammeter needs to be connected in series so the electron flow can be measured, and a voltmeter is most often used in parallel with the device or circuit being checked. Now get your meters ready as HMM
shows you next month how to tackle most, if not all, electrical problems in your muscle machine!
This article originally appeared in the June, 2005 issue of Hemmings Muscle Machines.
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