Electricity for the farm Part 8

30 carbon lamps, 16 candlepower, @60 1,800 2 lamps, 100 watt tungsten 200 Electric iron 400 Small water or milk heater 600 ------- Total current, 2nd house 3,000 1st house 9,100 ------- 12,100

Thus, in this plant, if every electrical device were turned on at once, the demand on the dynamo would be for 12.1 kilowatts, or an overload of over 100 per cent. The main-switch fuse, being for 60 amperes, would "blow" or melt, and cut off all current for the moment. To repair the damage would be merely the work of a second--and at a cost of a few cents--simply insert a new fuse, of which there must be a supply on hand at all times. Or, if either owner exceeded his capacity, the line fuses (one for 20 amperes, and the other for 40 amperes) would instantly cut off all current from the greedy one.

[Ill.u.s.tration: 25 and 40 watt Mazda tungsten lamps (1/4 scale)]

_Lessons From This Plant_

The story of this plant ill.u.s.trates two things which the farmer and his wife must take into account when they are figuring how much electricity they require. First, it ill.u.s.trates how one uses more and more current, as he finds it so serviceable and labor-saving, and at the same time free. The electric range and the water boiler, in the above instance, were later acquisitions not counted on in figuring the original installation. Second, it ill.u.s.trates, that while the normal load of this generator is _5.75_ kilowatts, one does not have to limit the electrical conveniences in the home to this amount. True, he cannot use more electricity than his plant will produce _at any one time_,--but it is only by a stretch of the imagination that one may conceive the necessity of using them all at once. Ironing, baking, and the use of small power are usually limited to daylight hours when no lights are burning.

As a matter of fact, this plant has proved satisfactory in every way; and only on one or two occasions have fuses been "blown", and then it was due to carelessness. A modern dynamo is rated liberally. It will stand an overload of as much as 100 per cent for a short time--half an hour or so. The danger from overloading is from heating. When the machine grows too hot for the hand, it is beginning to char its insulation, to continue which, of course would ruin it. The best plant is that which works under one-half or three-quarters load, under normal demands.

_Standard Voltage_

We are a.s.suming the farmer's plant to be, in 99 cases out of 100, the standard 110-volt, direct current type. Such a plant allows for at least a 10 per cent regulation, in voltage, up or down the scale; supplies for this voltage are to be had without delay in even the more remote parts of the country, and (being sold in greater volume) they are cheaper than those for other voltages.

There are two general exceptions to this rule as to 110-volt plants: (1) If the plant is located at a distance greater than a quarter of a mile from the house, it will be found cheaper (in cost of transmission line, as will be shown later) to adopt the 220-volt plant; (2), If the water supply is so meagre that it must be stored for many hours at a time, and then used for charging storage batteries, it will be found most economical to use a 30-volt plant. A storage battery is made up of cells of approximately 2 volts each; and, since more than 55 such cells would be required for a 110-volt installation, its cost would be prohibitive, with many farmers.

So we will a.s.sume that this plant is a 110-volt plant, to be run without storage battery. It will be well to make a chart, dividing the farm requirements into three heads--light, heat, and power.

_Light_

[Ill.u.s.tration: 60 and 100 watt Mazda tungsten lamp. These lamps may be had in sizes from 10 to 500 watts (1/4 scale)]

[Ill.u.s.tration: The lamp of the future. A 1000 watt Mazda nitrogen lamp, giving 2000 candlepower (1/4 scale)]

Light is obtained by means of incandescent lamps. There are two styles in common use, the carbon and the tungsten lamp. It requires 3.5 to 4 watts of electricity to produce one candlepower in a carbon lamp. It requires from 1 to 1.25 watt to produce one candlepower in the tungsten lamp. The new nitrogen lamp, not yet in general use, requires only 1/2 watt to the candlepower. Since tungsten lamps give three times the light of the carbon lamp, they are the most economical to use in the city or town where one is paying for commercial current.

But, in the country where water-power furnishes current for nothing, it will be found most economical to use the carbon lamp, since its cost at retail is 16 cents, as compared with 30 cents for a corresponding size in tungsten. A 60 watt carbon lamp, of 16 candlepower; or a 25 watt tungsten lamp, of 20 candlepower, are the sizes to use. In hanging lamps, as over the dining room table, a 100 watt tungsten lamp, costing 70 cents, and giving 92 candlepower light is very desirable; and for lighting the barn-yard, these 100 watt tungsten lamps should be used. For reading lamps, the tungsten style, of 40 or 60 watt capacity, will be found best. Otherwise, in all locations use the cheaper carbon lamp. Both styles have a rated life of 1,000 hours, after which they begin to fall off in efficiency. Here again, the farmer need not worry over lack of highest efficiency, as a lamp giving only 80 per cent of its rated candlepower is still serviceable when he is not paying for the current. With care not to use them at voltages beyond their ratings, lamps will last for years.

_A Specimen Light Allowance_

Below is a typical table of lights for a large farm house, the barns and barn-yard. It is given merely as a guide, to be varied for each individual case:

Watts Kitchen, 2 lights @60 watts 120 Dining room, 1 light, tungsten 100 Living room, table lamp with 3 tungstens @40 120 Living room, 2 wall fixtures, 4 lamps @60 watts 240 Parlor, same as living room 360 Pantry, 1 hanging lamp 60 Cellar, one portable lamp 60 Woodshed, 1 hanging lamp 60 2 bedrooms, 2 lights each @ 60 240 2 bed rooms, 1 light each @60 120 Bathroom, 1 "turn-down" light, @60 60 Hall, downstairs, 2 lights @60 120 Hall, upstairs, 1 light 60 Attic, 1 light 60 Porch, 1 light 60 Barn and barn-yard: Barn-yard entrance, 1 tungsten 100 Watering trough, 1 " 100 Front gate, 1 " 100 Horse barn, 4 lights @60 240 Cow barn, 4 lights @60 240 Pig house, 1 light 60 Hay barn, 2 lights, @60 120 ------- Total for farmstead 2,800

This provides for 44 lights, an extremely liberal allowance. How many of these lights will be burning at any one time? Probably not one-half of them; yet the ideal plant is that which permits all fixtures to be in service at one time on the rare occasions when necessary. Thus, for lighting only, 2,800 watts maximum service would require a 4 kilowatt generator, and 10 water horsepower, on the liberal rating of two to one. A 3 kilowatt generator would take care of these lights, with a 30 per cent overload (which is not excessive) for maximum service. The above liberal allowance of lights may be cut in two, or four--or even eight--and still throw a kerosene lamp in shadow. It all depends on the number of lights one wants burning at one time; and the power of the water wheel.

If the 36 carbon lights in the above table were replaced by 25 watt tungsten lights, the saving in power would be 35 watts each, or 1,260 watts, nearly two electrical horsepower; while the added first cost would be 14 cents a light, or $5.04. A generator of 2 kilowatt capacity would take care of all these lights then, with 460 watts to spare.

_Heating_

Electric heating and cooking is in its infancy, due to the prohibitive cost of commercial current in our cities. Here the farmer has the advantage again, with his cheap current.

For heating the house, it is calculated that 2 watts is required for each cubic foot of air s.p.a.ce in a room, during ordinary winter weather. Thus, a room 10 12, and 8 feet high, would contain 960 cubic feet, and would require 1,820 watts energy to heat it in cold weather. Five such rooms would require 9.1 kilowatts; and 10 such rooms, or their equivalent, would require 18.2 kilowatts.

Electric heating devices are divided into two cla.s.ses: (1) those which can be used on lamp circuits, _and do not draw more than 660 watts each_; and (2) those which draw more than 660, therefore _require special wiring_. The capacity of these devices is approximately as follows:

Lamp circuit devices: Watts Electric iron 400 to 660 Toaster 350 to 660 Vacuum cleaner 200 to 400 Grill 400 to 660 Small water heater 400 to 660 Hot plates 400 to 660

Lamp circuit devices: Coffee percolator 400 to 660 Chafing dish 400 to 660 Electric fan 100 to 250

Special circuit devices: Hot water boiler heater 800 to 1,200 Small ovens 660 to 1,200 Range ovens 1,200 to 3,000 Range, hot plates 400 to 1,300 Radiators (small) 750 to 1,500 Radiators (large) 1,500 to 6,000

The only device in the above list which is connected continuously, is the hot water boiler, and this can be credited with at least one electrical horsepower 24 hours a day. It is a small contrivance, not much bigger than a quart can, attached to the back of the kitchen boiler, and it keeps the water hot throughout the house at all hours.

Its cost will vary with the make, ranging from $8 to $15; and since it is one of the real blessings of the farm kitchen and bathroom, it should be included in all installations where power permits. Electric radiators will be used 24 hours a day in winter, and not at all in summer. They are portable, and can be moved from room to room, and only such rooms as are in actual use need be heated. The other devices are for intermittent service, many of them (like the iron) for only a few hours each week.

The grill, chafing dish, coffee percolator, etc., which are used on the dining room table while the family is at meals, each draw an equivalent of from 6 to 10 carbon lights. By keeping this in view and turning off spare lights, one can have the use of them, with even a small plant. Thus, a one kilowatt plant permits the use of any one of these lamp circuit devices at a time, with a few lights in addition.

_Power_

Electric power is to be had through motors. A direct current dynamo and a direct current motor are identical in construction. That is, a motor becomes a generator if belted to power; and a generator becomes a motor, if connected to electric mains. This is best ill.u.s.trated by citing the instance of a trans-continental railroad which crosses the Bitter Root Mountains by means of electric power. Running 200 miles up a 2 per cent grade, it is drawn by its motors. Coasting 200 miles down the 2 per cent grade on the other side of the mountains, its motors become generators. They act as brakes, and at the same time they pump the power of the coasting weight of this train back into the wires to help a train coming up the other side of the mountains.

[Ill.u.s.tration: Connections of shunt motor and starting rheostat]

Just as there are three types of direct current generators, so there are three types of direct current motors: _series_, _shunt_, and _compound_, with features already explained in the case of generators.

Motors are rated by horsepower, and generators are rated by kilowatts.

Thus a one kilowatt generator has a capacity of 1,000 watts; as a motor, it would be rated as 1000/746 horsepower, or 1.34 horsepower.

Their efficiency varies with their size, ranging from 40 to 60 per cent in very small motors, and up to 95 per cent in very large ones.

The following table may be taken as a guide in calculating the power required by motors, on 110-volt circuits:

1/4 Horsepower 2-1/2 amperes, or 275 watts 1/2 hp 4-1/2 amperes, or 500 watts 1 hp 9 amperes, or 990 watts 2 hp 17 amperes, or 1.97 kilowatts 3 hp 26 amperes, or 2.86 kilowatts 5 hp 40 amperes, or 4.40 kilowatts 7-1/2 hp 60 amperes, or 6.60 kilowatts 10 hp 76 amperes, or 8.36 kilowatts 15 hp 112 amperes, or 12.32 kilowatts

An electric motor, in operation, actually generates electricity, which it pushes back into the line as a counter-electromotive-force. The strength of this counter force, in volts, depends on the motor's speed, the same as if it were running as a dynamo. For this reason, when a motor is started, and before it comes up to speed, there would be a rush of current from the line, with nothing to hold it back, and the motor would be burned out unless some means were provided to protect it for the moment. This is done by means of a starting rheostat, similar to the regulating rheostat on the dynamo switchboard. This resistance box is connected in "series" with the armature, in the case of shunt and compound motors; and with the entire motor circuit in the case of a series machine.

A _series_ motor has a powerful starting torque, and adjusts its speed to the load. It is used almost altogether in street cars. It can be used in stump pulling, or derrick work, such as using a hay fork. It must always be operated under load, otherwise, it would increase in speed until it tore itself to pieces through mechanical strain. The ingenious farmer who puts together an electric plow, with the mains following behind on a reel, will use a series motor.

A _shunt_ motor should be used in all situations where a fairly uniform speed under load is required, such as separating, in milking machines, running a lathe, an ensilage cutter, vacuum cleaners, grinders, etc.

The _compound_ motor has the characteristics of the series and shunt motors, giving an increased starting torque, and a more nearly constant speed under varying loads than the shunt motor, since the latter drops off slightly in speed with increasing load.

_Flexible Power_

An electric motor is an extremely satisfactory form of power because it is so flexible. Thus, one may use a five horsepower motor for a one horsepower task, and the motor will use only one electrical horsepower in current--just enough to overcome the task imposed on it. For this reason, a large-sized motor may be used for any operation, from one requiring small power, up to its full capacity. It will take an overload, the same as a dynamo. In other words it is "eager" for any task imposed on it; therefore it must be protected by fuses, or it will consume itself, if too big an overload is imposed on it.

A one horsepower shunt or compound motor is very serviceable for routine farm operations, such as operating the separator, the churn, the milking machine, grinder, pump, and other small power jobs. Motors of 1/4 horsepower are handy in the kitchen, for grinding knives, polis.h.i.+ng silver, etc., and can be used also for vacuum cleaners, and running the sewing machine. For the larger operations, motors will vary from three horsepower for cutting ensilage, to fifteen horsepower for thres.h.i.+ng. They can be mounted on trucks and conveyed from one point to another, being fed current from the mains by means of suitable wires wound on reels.

Remember, in estimating the size of your plant for light, heat, and power, that it does not have to be big enough to use all the devices at one time. Also remember, that two water horsepower to one electrical horsepower is a very liberal allowance; and that a generator working under one-half or two-thirds capacity at normal loads will require less attention than a machine constantly being worked above its capacity. Therefore, let your generator be of liberal size, because the difference in cost between a 5 and 10 kilowatt machine is not in proportion to their capacity. In fact (especially among second-hand machines), the difference in cost is very small. The mere fact that the generator is of 110 electrical horsepower capacity does not require a turbine of 20 horsepower. The chances are that (unless you wish to heat your house and do large power jobs) you will not use more than 3 to 5 electrical horsepower normally; therefore an allowance of 10 water horsepower, in this case, would be ample. A plant used simply for lighting the house and barn, for irons, and toasters, and one horsepower motors, need not exceed 2 or 2-1/2 kilowatts for the generator, and 5 or 6 horsepower for the turbine wheel. Normally it would not use one-half this capacity.