Alternating Current vs. Direct Current
All the principles of generating electricity had been worked out in the 19th
Century, but by its end these had only just begun to produce electricity on
a large scale. The 20th Century has witnessed a colossal expansion of
electrical power generation and distribution. The general pattern has been
toward ever-larger units of production, using steam from coal- or oil-fired
boilers. Economies of scale and the greater physical efficiency achieved as
higher steam temperatures and pressures were attained both reinforced this
tendency. U.S. experience indicates the trend: in the first decade of the
century a generating unit with a capacity of 25,000 kilowatts with pressures
up to 200-300 pounds per square inch at 400°-500° F (about 200°-265° C) was
considered large, but by 1930 the largest unit was 208,000 kilowatts, with
pressures of 1,200 pounds per square inch at a temperature of 725° F, while
the amount of fuel necessary to produce a kilowatt-hour of electricity and
the price to the consumer had fallen dramatically.
As the market for electricity increased, so did the distance over which it
was transmitted, and the efficiency of transmission required higher and
higher voltages. The small direct-current generators of early urban power
systems were abandoned in favor of alternating-current systems, which could
be adapted more readily to high voltages. Transmission over a line of 155
miles (250 kilometers) was established in California in 1908 at 110,000
volts; Hoover Dam in the 1930s used a line of 300 miles (480 kilometers) at
287,000 volts. The latter case may serve as a reminder that hydroelectric
power, using a fall of water to drive water turbines, has been developed to
generate electricity where the climate and topography make it possible to
combine production with convenient transmission to a market. Remarkable
levels of efficiency have been achieved in modern plants.
One important consequence of the ever-expanding consumption of electricity
in the industrialized countries has been the linking of local systems to
provide vast power grids, or pools, within which power can be shifted easily
to meet changing local needs for current.
AC has other advantages:
So, while Thomas Edison receives the greater part of credit, it is clear
that we owe respect and gratitude for Nikola Tesla's creative and
- AC generators are simple, cheaper and more reliable than DC generators
- AC can readily be switched by circuit breakers at any voltage, whereas DC
can only be switched at low voltages
- AC motors and other electrical appliances are cheaper, simpler, and more
reliable than those designed to work with DC
- The frequency can be very precisely controlled and so AC is useful in motors
that require accurate speed eg. Clocks, tape recorders, VHS machines.
At a local radio shop Tesla bought 12 vacuum tubes, some wires and assorted resistors, and assembled them in a circuit box 24 inches long, 12 inches wide and 6 inches high, with a pair of 3-inch rods sticking out. Getting into the car with the circuit box in the front seat beside him, he pushed the rods in, announced, "We now have power," and proceeded to test drive the car for a week, often at speeds of up to 90 mph.
As it was an alternating-current motor and there were no batteries involved, where did the power come from?
The Forgotten Art of Electric - Powered Automobiles
by Arthur Abrom
Electric powered automobiles were one of the earliest considerations and this mode of propulsion enjoyed a brief but short reign. The development of electricity as a workable source of power for mankind has been studded with great controversy.
Thomas A. Edison was the first to start to market systems (i.e. electric generators) of any commercial value. His research and developmental skills were utilized to market a "direct current" system of electricity. Ships were equipped with D.C. systems and municipalities began lighting their streets with this revolutionary D.C. electric system. (At that time) Edison was the sole source of electricity!
While in the process of commercializing electricity, Thomas Edison hired men who knew of the new scientific gift to the world and were capable of new applications for electricity. One such man was a foreigner named Nikola Tesla. This man, although not known to many of us today, was without a doubt the greatest scientific mind that has ever lived. His accomplishments dwarfed even Thomas Edison's! Whereas Mr. Edison was a great experimenter, Mr. Tesla was a great theoretician. Nikola Tesla became frustrated and very much annoyed at the procedures Edison followed.
Tesla would rather calculate the possibility of something working (i.e. mathematical investigation) than the hit and miss technique of constant experimentation. So in the heat of an argument, he quit one day and stormed out of Edison's laboratory in West Orange, New Jersey.
Working on his own, Tesla conceived and built the first working alternating current generator. He, and he alone, is responsible for all of the advantages we enjoy today because of A.C. electric power.
Angered by Edison, Tesla sold his new patents to George Westinghouse for 15 million dollars in the very early 1900's. Tesla became totally independent and proceeded to carry on his investigative research in his laboratory on 5th Avenue in New York City.
George Westinghouse began to market this new system of electric generators and was in competition with Edison. Westinghouse prevailed because of the greater superiority of the A.C. generators over the less efficient D.C. power supplies of Thomas Edison. Today, A.C. power is the only source of electricity the world uses. And, please remember, Nikola Tesla is the man who developed it.
Now specifically dealing with automobiles in the infant days of their development, electric propulsion was considered and used. An electric powered automobile possessed many advantages that the noisy, cantankerous, smoke-belching gasoline cars could not offer.
First and foremost is the absolute silence one experiences when riding in an electrically powered vehicle. There is not even a hint of noise. One simply turns a key and steps on the accelerator - the vehicle moves instantly! No cranking from the start, no crank to turn (this was before electric starters), no pumping of the accelerator, no spark control to advance and no throttle linkage to pre-set before starting. One simply turned the ignition switch to on!
Second, is a sense of power. If one wants to increase speed, you simply depress the accelerator further - there is never any hesitation. Releasing the accelerator causes the vehicle to slow down immediately - you are always in complete control. It is not difficult to understand why these vehicles were so very popular around the turn of the century and until 1912 or so.
The big disadvantage to these cars was their range and need for re-charging every single night. All of these electric vehicles used a series of batteries and a D.C. motor to move itself about. The batteries require recharging every night and the range of travel was restricted to about 100 miles. Understand that this restriction was not a serious one in the early part of this century. Doctors began making house calls with electric cars (do you remember doctors making house calls?) because he no longer needed to tend to the horse at night time - just plug the car into an electric socket! No feeding, no rub-down and no mess to clean up!
Many of the large department stores in metropolitan areas began purchasing delivery trucks that were electrically powered. They were silent and emitted no pollutants. And, maintenance was a minimum on electrically powered vehicles. There were few mechanics and garages in operation in the early 1900's. So city life and travel appeared to be willing to embrace the electric automobile. Remember, these masterfully built vehicles all ran on D.C. current.
Two things happened to dampen the popularity of the electric automobile. One was the subconscious craving for speed that gripped all auto enthusisasts of this era. Each manufacturer was eager to show how far his car could travel (i.e. the transcontinental races) and what was its top speed!
Col. Vanderbilt constructed the first all concrete race track in Long Island and racing became the passion for the well-to-do. Newspapers constantly record new records of speed achieved by so-in-so. And, of course, the automobile manufacturers were quick to capitalize on the advertising effect of these new peaks of speed. Both of these events made the electrically powered vehicles appear to only belong to the "little old lady" down the street or the old retired gentleman who talked about the "good old days".
Electric vehicles could not reach speeds of 45 or 50 m.p.h. for this would have destroyed the batteries in moments. Bursts of speeds of 25 to 35 m.p.h. could be maintained for a moment or so. Normal driving speed-depending upon traffic conditions, was 15 to 20 m.p.h. by 1900 to 1910 standards, this was an acceptable speed limit to obtain from your electric vehicle.
Please note that none of the manufacturers of electric cars ever installed a D.C. generator. This would have put a small charge back into the batteries as the car moved about and would have thereby increased its operating range. This was considered by some to be approaching perpetual motion - and that, of course, was utterly impossible! Actually, D.C. generators would have worked and helped the electric car cause.
As mentioned earlier, Mr. Westinghouse's A.C. current generating equipment was being sold and installed about the country. The earlier D.C. equipment was being retired and disregarded. As a side note, Consolidated Edison Power Company of New York City still has one of Thomas Edison's D.C. generators installed in its 14th St. powerhouse - it still works! About this time, another giant corporation was formed and entered the A.C. generating equipment field - General Electric. This spelled the absolute end for Edison's D.C. power supply systems as a commercial means of generating and distributing electric power.
The electric automobile could not be adapted to accomodate and utilize a polyphase motor (i.e. A.C. power). Since they used batteries as a source of power, their extinction was sealed. No battery can put out an A.C. signal. True, a converter could be utilized (i.e. convert the D.C. signal from the battery to an A.C. signal), but the size of the equipment at this time was too large to fit in an automobile - even one with the generous dimensions of this era.
So, somewhere around 1915 or so, the electric automobile became a memory. True, United Parcel Service still utilizes several electric trucks in New York City today but the bulk of their fleet of vehicles utilizes gasoline or diesel fuel. For all intensive purposes, the electrically powered automobile is dead - they are considered dinosaurs of the past.
But, let us stop a moment and consider the advantages of utilizing electric power as a means of propelling vehicles. Maintenance is absolutely minimal for the only oil required is for the two bearings in the motor and the necessary grease fittings. There is no oil to change, no radiator to clean and fill, no transmission to foul up, no fuel pump, no water pump, no carburetion problems, no muffler to rot out or replace and no pollutants emitted into the atmosphere. It appears as though it might be the answer we have been searching for!
Therefore, the two problems facing us become top speed and range of driving - providing, of course, the A.C. and D.C. problems could be worked out. With today's technology this does not seem to be insurmountable. In fact, the entire problem has already been solved - in the past, the distant past and the not so distant! Stop! Re-read the last sentence again. Ponder it for a few moments before going on.
Several times earlier in this article, I mentioned the man, Nikola Tesla and stated that he was the greatest mind that ever lived. The U.S. Patent Office has 1,200 patents registered in the name of Nikola Tesla and it is estimated that he could have patented an additional 1,000 or so from memory!
But, back to our electric automobiles - in 1931, under the financing of Pierce-Arrow and George Westinghouse, a 1931 Pierce-Arrow was selected to be tested at the factory grounds in Buffalo, N.Y. The standard internal combustion engine was removed and an 80-H.P. 1800 r.p.m electric motor installed to the clutch and transmission. The A.C. motor measured 40 inches long and 30 inches in diameter and the power leads were left standing in the air - no external power source!
At the appointed time, Nikola Tesla arrived from New York City and inspected the Pierce-Arrow automobile. He then went to a local radio store and purchased a handful of tubes (12), wires and assorted resistors. A box measuring 24 inches long, 12 inches wide and 6 inches high was assembled housing the circuit. The box was placed on the front seat and had its wires connected to the air-cooled, brushless motor. Two rods 1/4" in diameter stuck out of the box about 3" in length.
Mr. Tesla got into the driver's seat, pushed the two rods in and stated, "We now have power". He put the car into gear and it moved forward! This vehicle, powered by an A.C. motor, was driven to speeds of 90 m.p.h. and performed better than any internal combustion engine of its day! One week was spent testing the vehicle. Several newspapers in Buffalo reported this test. When asked where the power came from, Tesla replied, "From the ethers all around us". Several people suggested that Tesla was mad and somehow in league with sinister forces of the universe. He became incensed, removed his mysterious box from the vehicle and returned to his laboratory in New York City. His secret died with him!
It is speculated that Nikola Tesla was able to somehow harness the earth's magnetic field that encompasses our planet. And, he somehow was able to draw tremendous amounts of power by cutting these lines of force or causing them to be multiplied together. The exact nature of his device remains a mystery but it did actually function by powering the 80 h.p. A.C. motor in the Pierce-Arrow at speeds up to 90 m.p.h. and no recharging was ever necessary!