Electricity for the farm / Light, heat and power by inexpensive methods from the water wheel or farm engine

by Frederick Irving Anderson

The Standard Voltage Set

In response to a general demand, the first type (the direct-connected standard voltage set) has been developed to a high state of efficiency recently, and is to be had in a great variety of sizes (ranging from one-quarter kilowatt to 25 kilowatts and over) from many manufacturers.

The principle of the gasoline engine as motive power is so familiar to the average farmer that it needs but a brief description here. Gasoline or other fuel (oil, gas, or alcohol) is transformed into vapor, mixed with air in correct proportions, and drawn into the engine cylinder and there exploded by means of a properly-timed electric spark.

Internal combustion engines are of two general types—four-cycle and two-cycle. The former is by far the more common. In a four-cycle engine the piston must travel twice up and down in each cylinder, to deliver one power stroke. This results in one power impulse in each cylinder every two revolutions of the crank shaft. On its first down stroke, the piston sucks in gas. On its first up stroke, it compresses the gas. At the height of this stroke, the gas is exploded by means of the electric spark and the piston is driven down, on its power stroke. The fourth stroke is called the scavening stroke, and expels the burned gas. This completes the cycle.

A one-cylinder engine of the ordinary four-cycle type has one power stroke for every two revolutions of the fly wheel. A two-cylinder engine has one power stroke for one revolution of the fly wheel; and a four-cylinder engine has two power strokes to each revolution. The greater the number of cylinders, the more even the flow of power. In automobiles six cylinders are common, and in the last year or two, eight-cylinder engines began appearing on the market in large numbers. A twelve-cylinder engine is the prospect for the immediate future.

Since the dynamo that is to supply electric current direct to lamps requires a steady flow of power, the single-cylinder gas or gasoline engine of the four-cycle type is not satisfactory as a rule. The lights will flicker with every other revolution of the fly wheel. This would be of no importance if the current was being used to charge a storage battery—and right here lies the reason why a cheaper engine may be used in connection with a storage battery than when the dynamo supplies the current direct for lighting.

A two-cylinder engine is more even in its flow of power and a four-cylinder engine still better. For this reason, standard voltage generating sets without battery are usually of two or four cylinders when of the four-cycle type. When a single-cylinder engine is used, it should be of the two-cycle type. In the two-cycle engine, there is one power stroke to each up-and-down journey of the piston. This effect is produced by having inlet and exhaust ports in the crank case, so arranged that, when the piston arrives at the bottom of the power stroke, the waste gases are pushed out, and fresh gas drawn in before the up stroke begins.

For direct lighting, the engine must be governed so as not to vary more than five per cent in speed between no load and full load. There are many makes on the market which advertise a speed variation of three per cent under normal loads. Governors are usually of the centrifugal ball type, integral with the fly wheel, regulating the amount of gas and air supplied to the cylinders in accordance with the speed. Thus, if such an engine began to slow down because of increase in load, the centrifugal balls would come closer together, and open the throttle, thus supplying more gas and air and increasing the speed. If the speed became excessive, due to sudden shutting off of lights, the centrifugal balls would fly farther apart, and the throttle would close until the speed was again adjusted to the load.

These direct-connected standard voltage sets are as a rule fitted with the 110-volt, direct current, compound type of dynamo, the duplicate in every respect of the machine described in previous chapters for water-power plants. They are practically automatic in operation and will run for hours without attention, except as to oil and gasoline supply. They may be installed in the woodshed or cellar without annoyance due to noise or vibration. It is necessary to start them, of course, when light or power is desired, and to stop them when no current is being drawn. There have appeared several makes on the market in which starting and stopping are automatic. Storage batteries are used in connection with these latter plants for starting the engine. When a light is turned on, or current is drawn for any purpose, an automatic switch turns the dynamo into a motor, and it starts the engine by means of the current stored in the battery. Instantly the engine has come up to speed, the motor becomes a dynamo again and begins to deliver current. When the last light is turned off, the engine stops automatically.

Since the installation of a direct-connected standard voltage plant of this type is similar in every respect, except as to motive power, to the hydro-electric plant, its cost, with this single exception, is the same. The same lamps, wire, and devices are used.