|The Stovebolt Page||
By Jerry Herbison
Terms and Definitions
-- a refresher!
Before we get started into troubleshooting and adjusting tips, let's review a few terms so we're all on the same page in the hymnal, so to speak! An electrical circuit can't be seen in operation so we must use a standard set of definitions to describe what's going on. It's very simple to dismantle an engine or transmission and see what's happening with the pistons, valves, gears, etc., but that just can't be done with electrons. Let's begin with some basic definitions and apply them to something that's easy for an electrical novice to understand, a plumbing system. Bear with me if you're familiar with all these terms because I'm sure a few of us could use a refresher course.
Current flow is measured in amperes which would correspond to the volume of water flowing down the pipe in our plumbing system. Let's assume the pipe we're dealing with is able to flow 50 gallons of water per hour at a particular pressure. If we want to flow more water, we must either raise the pressure, or use a bigger pipe at the same pressure. The same assumption holds true for an electrical circuit. A conductor (pipe) of a specific size can flow a certain amount of amperage with a set voltage without overloading itself. If we want to flow more amps, we could apply a higher voltage, but we run the risk of trying to force more electrons along the wire than it can handle safely, resulting in an overheated wire and possibly a fire. In that case, a bigger conductor would be needed. This is why starter cables are large, multi-strand wires, while tail lights, etc., can get by with much smaller conductors. We wouldn't try to put out a house fire with a garden hose, nor would we want to run a starter on a #12 wire. It's just not up to the task at hand!
Resistance is the opposition to current flow, measured in a term called "Ohms." It's like the rust in our water pipe, and opposes the flow of current, or water, as the case may be. There is a definite relationship between voltage, current, and resistance, which is expressed in something called "Ohm's Law." Resistance in an electrical circuit diagram will be represented by a number, followed by a symbol resembling an upside-down horseshoe. It's the Greek letter "Omega." Ohm's Law states that one volt will cause one amp of current to flow through one ohm of resistance. Since these values can be measured and confirmed, Ohm's Law is a "Law" of physics, not a "theory" or "hypothesis" which are educated guesses, with no way of being positively proved. The direction of current flow in a wire is a "theory," since no one has actually observed whether electrons flow from positive to negative, or vice versa! We know what electricity does, and we can make an educated guess as to how it happens, but there are still a lot of mysteries to be solved about basic electricity.
Power, expressed in "Watts" is a measure of how much work an electrical system is able to accomplish. It is calculated by multiplying the voltage present in a circuit times the amperage which is flowing. For instance, a 12-volt circuit which is flowing 10 amps of current is producing 120 Watts of power. The resistance of the circuit in this situation would be 1.2 Ohms, the amount of resistance which would result in a 10-amp current flow with 12 volts applied. Let's look at a circuit that we're all pretty familiar with, the starter. An average 6-volt starter will draw about 250 amps of cranking current on a cold start, and the battery voltage will drop to 5 volts or a little less during cranking due to the load placed on the battery. That's a power output of 1,250 watts! No wonder we need a well-charged battery, clean, tight connections, and big battery cables! In the starting circuit mentioned above, using Ohm's law, we find that the resistance of the starter is only 2/100 Ohm! That's almost a dead short, which means the starter is running in a severe overload all the time. If an engine isn't well-tuned, and we must crank it with the starter for a long time to get it running, it's very likely that starter and battery problems will happen. The absolute maximum time a starter should be operated is 30 seconds, with a 20-minute cool-down time afterwards!
I mentioned a "series resistance test" as part of a checkout of a charging system. As soon as I get the old digital camera cranked up again, we're going to begin using our knowledge of Ohm's Law in a practical application to find out if there are any bad connections or conductors between the generator and the battery. It's like checking on why the water in the bathtub is running so slowly through those 50-year-old pipes at home! (Hint - - - - - the reasons for the problem performance are pretty similar!)
Jerry Herbison is
from Dellrose, Tennessee currently operating "Action Enterprises,"
a racing engine and gunsmithing business located at his farm in rural south
central Tennessee. Jerry spent 15 years as a high school auto mechanics instructor
and has ASE certifications, Master Technician certification in Automotive, Heavy
Truck, Auto Body, Engine Machining, and Advanced Engine Performance. He grew
up around a large independent automotive shop in Nashville in the 1950's, and
has been associated with the auto repair trade since then. He's worked as an
industrial maintenance technician, aircraft electronics technician (US Air Force),
industrial electrician, welder, machinist, truck driver, and short-order cook!
Jerry's putting together a series of articles on charging systems each dealing with a separate area of inspecting and maintaining the oldtime DC systems. He has a pretty extensive library of research material and specifications on these systems, some going back into the 1940's. His father, who went into business in 1945, is still living, and is a deep well of information on the older systems. He was the chief automotive instructor at Nashville Auto-Diesel College for several years in the 1960's and opened the high school shop where Jerry ended up teaching in 1971.
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