Electrical Basics You Need to Know allel section of the circuit will be quite close to the voltage at the beginning of the circuit. It’s not too hard to see that by using series-parallel circuits, manufacturers can save a lot of money on switches, wire, and circuit protectors, but series-parallel circuits also greatly simplify a boat’s overall electrical system, with no sacrifice in performance or safety.
Circuit Protector
Switch “On”
Switch “On”
Switch “On”
Battery
Cabin Light
Ohm’s Law and What It Can Tell Us
Switch “On”
Cabin Light
Cabin Light
Fig. 1-5. A series-parallel circuit as found on your boat.
Georg Simon Ohm (1787–1854), a German physicist, was one of the great early experimenters with electricity. He left us with the simple but oh-so-important mathematical formula that bears his name. Ohm’s law helps us to understand the relationship between the measurable forces in electricity. Once we are armed with a clear understanding of the relationships between the different elements in this formula, we will have made a giant step forward in our ability to understand and locate electrical problems. As we work with this invisible thing called electricity, we need to get used to dealing in an abstract way with the stuff. We’ll be taking a lot of measurements with a multimeter, and we will learn to translate these measurements into meaningful information. Throughout the rest of this book I demonstrate the correct methods of obtaining accurate electrical measurements with a multimeter, and I try to provide an understanding of what these measurements mean. First, however, we must get the definitions of a few electrical terms clear in our heads, and then become completely familiar with this wonderful thing called Ohm’s law.
The Key Players There are four terms that will continually crop up in any discussion of things electrical: volts, amps, ohms, and watts. Each of these terms represents an electrical value and is named after an early experimenter in electricity. These are the people who captured the concept of electricity and made it useful to people like you and me who own boats. There is a fifth term, also named after an early experimenter, that’s gaining favor with the knowledgeable and trendy among us, the joule. The unit of electrical resistance, the ohm, was named for Georg Ohm, the German scientist who gave us Ohm’s law. The electrical symbol used to express the value for ohms is the Greek letter omega, shown in figure 1-6 on page 6. When used in Ohm’s law, however, resistance is represented by a capital R. Alessandro Volta (1745–1827) was an Italian physicist who gave us the unit of electrical force called the volt. The electrical symbol for volts is so simple that it doesn’t need an illustration; it’s just a capital V. However, when used in the formula for Ohm’s law, voltage is represented by a capital P, which stands for potential. 5
