The Age of the Electric Horse

By Earl Hunsinger

A few centuries ago, or even one, when a farmer wanted to plow his field, he used his one horsepower tractor (better known as a horse and plow). When going to town, he may have traveled in a two horsepower vehicle (a wagon pulled by two horses). And when it came time to thresh his grain, he might have used a six horsepower machine to do this (six horses hitched to a rotating thresher). Today, gasoline and diesel powered engines have replaced these more traditional methods of doing things. Yet most machinery today is still rated in comparison with how many horses it supposedly replaces. Even lawnmowers and chainsaws are rated in horsepower.

For most residential, commercial, and industrial applications, electric motors (rated in horsepower) have replaced the use of horses, or the work done by people. In addition, electricity and the horsepower embodied in electrical motors have been applied in ways that the farmer of a century ago could never have imagined.

What we call modern civilization would be impossible without electricity. If electricity is the lifeblood of today’s world, the relationship between electricity and magnetism is the driving force that keeps that blood moving and that allows it to be so universally utilized.

Early in the 19th century, it was recognized that when electricity flows through a wire, it creates a magnetic field. For instance, a compass needle would be deflected if held near the wire. Forming the wire into a coil, such as by wrapping it around a nail, would create a stronger magnet. Eventually it was realized that if the direction that the electricity flowed through the wire was reversed, the magnetic poles would also be reversed.

This ability to create a magnet, and determine its north and south poles, simply by flipping a switch, led to the invention of one of the most ubiquitous devices of the last hundred years, the electric motor. Anyone that has ever played with magnets knows that unlike or opposite poles attract and like poles repel. To understand how this can be used to produce motion, imagine a magnet suspended by a string. If it is dangled over another magnet, the unlike poles will be attracted to each other and the magnet will spin until they are close together. This is essentially how a motor is created. In a common type of electric motor, wire is wound into coils and connected to a source of electricity to create magnets that can be turned on and off and have their poles reversed. These "electromagnets" are mounted in a circular frame. A rotating shaft is mounted on bearings inside this circular frame. Attached to this shaft are additional coils of wire used as electromagnets. The shaft is fixed very securely so that as it spins the rotating electromagnets can come very close to the stationary electromagnets without touching them. Just as with our regular magnet on a string, when the electromagnets are turned on, the unlike poles are attracted to each other. This causes the shaft to spin. However, unlike our permanent magnet on a string, these electromagnets can have their poles reversed by changing the direction of the electrical current. As soon as the unlike poles get close together, they become like poles and repel each other. By very precisely reversing the electrical current flow to each of the magnets, the shaft can be made to spin rapidly. This rotating motion can then be used to drive fans, pumps, and much of the machinery used in the modern world. Such electrical motors are used everywhere today, from the small, fractional horsepower motors used in household appliances to the large, thousand horsepower motors used in industry.

Today, most horses live a life of leisure, kept only to be ridden for recreation. The work they once did is accomplished by mechanical machinery. The simple ability to create a magnet with a piece of wire and a source of electricity has been one of the main factors that has put them out of a job, and has ushered in the age of the electric horse.