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| Getting what the designer wants. |
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There are times when you want high electrical pressure or voltage to do a job.
There are also times when you want high volumes of electrons or amperage to do a job.
The designer of the electrical system knows what he is looking for and how to get it by using various electrical modifiers such as transformers, oscillators, coils, resistors, capacitors, etc.
In terms of the car, high pressure is needed to force electrons to jump the gap at the rotor tip and at the spark plug gap. High flow is needed to provide a massive volume of electrons to turn the starter motor, air conditioning motor and other devices. It takes different kinds and types of wire to do these different jobs. Basically, it takes heavy, large diameter wire to allow large electron flow. It takes smaller diameter wire to carry small flows of electrons at high pressures.
It takes thinner, less "dielectrically strong" insulation to prevent the escape of electrons in low-pressure, low-voltage applications. It takes thicker, more dielectrically strong insulation to keep the electrical pressure from leaping from the wire to the ground in high-voltage applications.
These are the basic reasons for the differences in wire types and configurations. Depending upon pressure and flow, you need different amounts of wire and insulation. With high volumes of electrons, you need thicker wire. With high-pressure electrons, you need thicker insulation. (See Fig. 4.)
| LARGE FLOW | HIGH PRESSURE |
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| WIRE SIZE | LARGE DIAMETER |
SMALL DIAMETER IS OK |
| INSULATION | THIN INSULATION IS OK |
THICK INSULATION |
| EXAMPLE | BATTERY CABLE |
SPARK PLUG WIRE |
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Fig. 4
| Electrical flow types. |
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When all of the electrons are flowing down a wire in one direction, it is called direct current. There is another type of electrical flow called alternating current (AC) in which the flow of electrons flows one way first and then reverses direction to flow backwards. Various electrical devices--motors, light bulbs, etc.--can be designed to make use of either type of electrical flow, but typically not both. They work with either direct current or alternating current. In general, however, it is the mere movement of electrons which creates some useful work--and not the direction of electron flow.
The movement of electrons creates heat (in a toaster, for instance), light (in a light bulb), magnetic field (in an electric motor) or induced current (in an automotive coil) and so forth. The key is movement of electrons.
Direct current or one-way current is supplied by simple storage devices such as automotive batteries. Thus, direct current from the battery is the basic electrical source for all electrical and electronic devices on the car.
| Recap |
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The type of electricity used in the car is direct current, which flows out of the battery. The typical modern car uses a 12-volt battery for the electrical system.
Electricity has properties which allow it to perform different types of work. For instance, in order to move electrons long distances over a wire, large amounts of electrical pressure, measured in volts are required. This same property is used to cause electrons to leap across the resistance of the spark plug gap--the resistance being measured in ohms.
Electrical volume is measured in amps or amperes. The volume required to do work on the car can vary all the way from a small 1- or 2-amp load to light a light bulb, up to a 200-amp load to turn the starter motor on a 4-cylinder car.
| Radio Frequency Interference (RFI)--"Static." |
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Alternating current has a number of advantages over direct current when its properties are compared for "normal" use in the real world. For example, with AC, it is easier to move high amounts of electricity over large distances.
Alternating current, in spite of its obvious superiority for long distance transmission, creates at least one major problem in many applications: radio frequency interference (RFI), commonly known as "static." This is a problem which must be dealt with by automotive designers and professional mechanics.
RFI occurs when alternating current of sufficient power flows through a wire to cause a problem. RFI is created in any wire through which a variation in current occurs. However, if the electrical power value is very low, the RFI may be so weak as to be insignificant.
With modern technology, however, the term RFI is used less and less. RFI typically refers to signals which truly affect radio or TV reception. However, you don't have to hear or see static to have electrical interference. Significantly lower levels of power can cause problems, and it is usually called "electromagnetic interference" or "EMI."
| How much power is sufficient to be a problem? |
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An example of "sufficient power" is an electric drill used by your next-door neighbor which causes "snow" to show up on your TV screen. This occurs because the electric motor in the drill is using an AC motor to do its work. Remember, that's a fractional horsepower motor doing the job, but it still generates plenty of RFI.
Or, you may be driving in your car listening to your AM radio when you hear a buzzing sound over the speaker. This RFI is often caused by a nearby car which has problems with its plug wires or secondary part of its ignition system. Or, it is using non-suppressive wires. In any case, it is RFI which is causing this problem.
It is a varying flow of current--one which pulsates--that causes RFI to be transmitted.
