Page 40 - Electromechanical Devices and Components Illustrated Sourcebook

2 Electromechanical Devices & Components Illustrated Sourcebook

Most of us have some basic knowledge of electricity because + −
of the many electrical gadgets and appliances that we use
No Flow
every day. We know that when we flip on a light switch, elec-
tricity is supplied to a lamp and it produces light. We turn on
the blender and the motor starts to turn. Flashlights use bat-
teries as their power source and when they run down, they
don’t produce enough electricity to light the bulb.
In fact most of us have a slightly more advanced knowl-
edge of electricity than we may realize. You have probably
noticed that most electrical devices have two wires feeding
power to them, or that light bulbs have a brilliant glow and
Battery Knife Switch Light Bulb
they are very hot during operation. If you leave the car’s lights
on overnight you know that the battery will be dead the next Figure 1-2 Open Circuit
morning. You may also be aware that a car operates on 12 volts
DC and the outlets in the house supply 120 volts AC.

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The Electric Circuit Electron Flow

In order to better utilize the information presented in this
book, it is necessary to have a basic understanding of elec-
tricity and how it can be applied to work with, or provide con-
trol for, mechanical devices.
To better understand electricity, let’s first consider the
basic electric circuit. All electrical circuits have two things in
common, they have a power source and something that is
using that power, generally referred to as the load. In Figure 1-1
the power source is a battery and the load is a light bulb. The Battery Knife Switch Light Bulb
battery supplies energy to the light bulb and the bulb’s fila- Figure 1-3 Closed Circuit
ment glows. In this arrangement, the stored energy of the bat-
tery is transformed into something useful, light. Electrons
flow from the negative terminal (–) of the battery through the
light bulb filament and back to the positive terminal (+). Voltage, Current, and Resistance
To make the basic electrical a little more friendly, a switch
is applied to the circuit. The switch is much like a valve for Now that we have an understanding of the basic electric cir-
electrons. When the switch is open, as shown in Figure 1-2, cuit, there are a few items that will provide us with a better
the flow of electrons is interrupted and the lamp is off. This working knowledge of how electricity does what it does.
mode is usually referred to as an open circuit. When considering electric circuits there are three different
To turn the lamp on, the switch is closed and the electrons parameters that are important. Each of these parameters
can flow again, as shown in Figure 1-3. This mode is gener- works in conjunction with the other two, therefore all three
ally referred to as a closed circuit. The switch provides ready must be considered in every electrical circuit. These param-
convenience in operating the circuit. eters are voltage, current, and resistance. Voltage is the
parameter that is most commonly known. Cars generally
operate on 12 volts, the outlets in your house supply 120
+ −
volts and major appliances like stoves and dryers operate on
Electron Flow 220 volts. The second parameter is current. The unit of mea-
sure for current is amperes or amps. The current rating
found on the circuit breakers in the electrical panel at your
house are rated in amperes. A circuit breaker which is
labeled 20 is designed to carry a maximum current of 20 amps.
The small fuses in your car are also rated in amps. If a fuse
is printed with 15 it is designed to carry a maximum current
of 15 amps. The third, and least known, parameter is resis-
tance. Resistance is just what the word implies, resistance to
the flow of electricity. The unit of measure for resistance is
ohms. Since resistance is what allows us to extract work
Battery Light Bulb from an electrical circuit, it is an exceptionally important
Figure 1-1 Basic Electric Circuit parameter to understand.