THE ELECTRIC PLANT AT WORK
Direct-connected generating sets--Belt drive--The
switchboard--Governors and voltage regulators--Methods of achieving
constant pressure at all loads: Over-compounding the dynamo; A
system of resistances; (A home-made electric radiator); Regulating
voltage by means of the rheostat--Automatic devices--Putting the
plant in operation.
Dynamos may be connected to water wheels either by means of a belt, or
the armature may spin on the same shaft as the water wheel itself. The
latter is by far the more desirable way, as it eliminates the loss of
power through shafting and belting, and does away altogether
with the belts themselves as a source of trouble. An installation
with the water wheel and armature on the same shaft is called a
"direct-connected set" and is of almost universal use in large power
plants.
To be able to use such a direct-connected set, the dynamo must be
designed to develop its full voltage when run at a speed identical
with that of the water wheel. That is, if the dynamo is wound to be
run at a speed of 800 revolutions per minute, it must be driven by a
water wheel which runs at this speed and can be governed within narrow
limits. Small impulse wheels running under great heads attain high
speed, and for such wheels it is possible to obtain a suitable dynamo
at low cost. For instance, a 12-inch impulse wheel, running under a
200-foot head will develop 6-3/4 horsepower when running at a speed of
875 revolutions per minute. A dynamo for direct coupling to such a
wheel should have a rated speed within 5 per cent of 875 r.p.m.; and,
as generators of this speed are to be had from the stock of almost all
manufacturers, there would be no extra charge.
When it comes to the larger wheels, however, of the impulse type, or
to turbines operating under their usual head the question becomes a
little more difficult. In such cases, the speed of the water wheel
will vary from 150 revolutions per minute, to 400, which is slow
speed for a small dynamo. As a general rule, the higher the speed of a
dynamo, the lower the cost; because, to lower the speed for a given
voltage, it is necessary either to increase the number of conductors
on the armature, or to increase the number of field coils, or both.
That means a larger machine, and a corresponding increase in cost.
In practice, in large plants, with alternating-current machines it has
become usual to mount the field magnets on the shaft, and build the
armature as a stationary ring in whose air space the field coils
revolve. This simplifies the construction of slow-speed, large-output
dynamos. Such a machine, however, is not to be had for the modest
isolated plant of the farmer with his small water-power.
[Illustration: Instantaneous photograph of high-pressure water jet
being quenched by buckets of a tangential wheel]
[Illustration: A tangential wheel, and a dynamo keyed to the same
shaft--the ideal method for generating electricity. The centrifugal
governor is included on the same base]
Dynamos can be designed for almost any waterwheel speed, and, among
small manufacturers especially, there is a disposition to furnish
these special machines at little advance in price over their stock
machines. Frequently it is merely a matter of changing the winding on
a stock machine. The farmer himself, in many cases, can re-wind an old
dynamo to fit the speed requirements of a direct-connected drive if
the difference is not too great. All that would be necessary to
effect this change would be to get the necessary winding data from the
manufacturer himself, and proceed with the winding. This data would
give the gauge of wire and the number of turns required for each spool
of the field magnets; and the gauge of wire and number of turns
required for each slot in the armature. The average boy who has
studied electricity (and there is something about electricity that
makes it closer to the boy's heart than his pet dog) could do this
work. The advantages of direct drive are so many that it should be
used wherever possible.
When direct drive cannot be had, a belt must be used, either from a
main shaft, or a countershaft. The belt must be of liberal size, and
must be of the "endless" variety--with a scarfed joint. Leather belt
lacing, or even the better grades of wire lacing, unless very
carefully used, will prove unsatisfactory. The dynamo feels every
variation in speed, and this is reflected in the lights. There is
nothing quite so annoying as flickering lights. Usually this can be
traced to the belt connections. Leather lacing forms a knot which
causes the lights to flicker at each revolution of the belt. The
endless belt does away with this trouble. Most dynamos are provided
with sliding bases, by which the machine can be moved one way or
another a few inches, to take up slack in the belt. To take advantage
of this, the belt must be run in a horizontal line, or nearly so.
Vertical belting is to be avoided.
The dynamo is mounted on a wooden base, in a dry location where it is
protected from the weather, or dampness from any source. It must be
mounted firmly, to prevent vibration when running up to speed; and the
switchboard should occupy a place within easy reach. Wires running
from the dynamo to the switchboard should be protected from injury,
and must be of ample size to carry the full current of the machine
without heating. A neat way is to carry them down through the flooring
through porcelain tubes, thence to a point where they can be brought
up at the back of the switchboard. If there is any danger of injury to
these mains they may be enclosed in iron pipe. Keep the wires out of
sight as much as possible, and make all connections on the back of the
switchboard.
_The Switchboard_
[Illustration: Connecting switchboard instruments]
The switchboard is constructed of some fireproof material, preferably
slate or marble. When the cost of this material is an item to
consider, build a substantial wooden frame for your switchboard. You
can then screw asbestos shingles to this to hold the various
instruments and with a little care such a switchboard can be made to
look business-like, and it is fully as serviceable as the more
expensive kind. The switchboard instruments have already been
described briefly. They consist of a voltmeter (to measure voltage);
an ammeter (to measure the strength of the current drawn, in amperes),
a rheostat (to regulate the voltage of the machine to suit the
individual requirements); and the usual switches and fuses. The main
switch should be so wired that when open it will throw all the current
off the line, but still leave the field coils, the voltmeter, and the
switchboard lamp in circuit. The main-switch fuses should have a
capacity about 50 per cent in excess of the full load of the dynamo.
If the machine is rated for 50 amperes, 75-ampere fuses should be
installed. This permits throwing on an overload in an emergency; and
at the same time guards against a short circuit. If the capacity of
the machine is under 30 amperes, plug fuses, costing 3 cents each, can
be used. If it is above this capacity, cartridge fuses, costing a
little more, are required. A supply of these fuses should be kept
handy at all times.
_Governors and Voltage Regulators_
[Illustration: A centrifugal governor (Courtesy of the C. P. Bradway
Company, West Stafford, Conn.)]
The necessity for water wheel governors will vary with conditions. As
a general rule, it may be said that reaction turbines working under a
low head with a large quantity of water do not require as much
governing as the impulse wheel, working under high heads with small
quantities of water. When governing is necessary at all, it is because
the prime mover varies in speed from no load to full load. Planning
one's plant with a liberal allowance of power--two water horsepower to
one electrical horsepower is liberal--reduces the necessity of
governors to a minimum. As an instance of this, the plant described
in some detail in Chapters One and Six of this volume, runs without a
governor.
However, a surplus of water-power is not usual. Generally plants are
designed within narrow limits; and then the need of a governor becomes
immediately apparent. There are many designs of governors on the
market, the cheapest being of the centrifugal type, in which a pair of
whirling balls are connected to the water wheel gate by means of
gears, and open or close the gate as the speed lowers or rises.
Constant speed is necessary because voltage is directly dependent on
speed. If the speed falls 25 per cent, the voltage falls likewise; and
a plant with the voltage varying between such limits would be a
constant source of annoyance, as well as expense for burned-out lamps.
Since constant voltage is the result aimed at by the use of a
governor, the same result can be attained in other ways, several of
which will be explained here briefly.
_Over-Compounding_
(1) Over-compounding the dynamo. This is simple and cheap, if one buys
the right dynamo in the first instance; or if he can do the
over-compounding himself, by the method described in the concluding
paragraphs of Chapter Seven. If it is found that the speed of the
water wheel drops 25 per cent between no load and full load, a dynamo
with field coils over-compounded to this extent would give a fairly
constant regulation. If you are buying a special dynamo for direct
drive, your manufacturer can supply you with a machine that will
maintain constant voltage under the normal variations in speed of your
wheel.
_A System of Resistances_
(2) Constant load systems. This system provides that the dynamo shall
be delivering a fixed amount of current at all times, under which
circumstances the water wheel would not require regulation, as the
demands on it would not vary from minute to minute or hour to hour.
This system is very simply arranged. It consists of having a set of
"resistances" to throw into the circuit, in proportion to the amount
of current used.
Let us say, as an example, that a 50-ampere generator is used at a
pressure of 110 volts; and that it is desirable to work this plant at
80 per cent load, or 40 amperes current draft. When all the lights or
appliances were in use, there would be no outside "resistance" in the
circuit. When none of the lights or appliances were in use (as would
be the case for many hours during the day) it would be necessary to
consume this amount of current in some other way--to _waste it_. A
resistance permitting 40 amperes of current to flow, would be
necessary. Of what size should this resistance be?
The answer is had by applying Ohm's Law, explained in Chapter Five.
The Law in this case, would be read R = E/C. Therefore, in this case R
= 110/40 = 2-3/4 ohms resistance, would be required, switched across
the mains, to keep the dynamo delivering its normal load.
The cheapest form of this resistance would be iron wire. In place of
iron wire, German silver wire could be used. German silver wire is to
be had cheaply, and is manufactured in two grades, 18% and 30%, with a
resistance respectively 18 and 30 times that of copper for the same
gauge. Nichrome wire has a resistance 60 times that of copper; and
manganin wire has a resistance 65 times that of copper, of the same
gauge.
First figure the number of feet of copper wire suitable for the
purpose. Allowing 500 circular mills for each ampere, the gauge of the
wire should be 40 × 500 = 20,000 circular mills, or approximately No.
7 B. & S. gauge. How many feet of No. 7 copper wire would give a
resistance of 2-3/4 ohms? Referring to the copper wire table, we find
that it requires 2006.2 of No. 7 wire to make one ohm. Then 2-3/4 ohms
would require 5,517 feet.
Since 30 per cent German silver wire is approximately 30 times the
resistance of copper, a No. 7 German silver wire, for this purpose,
would be 1/30 the length of the copper wire, or 186 feet. If nichrome
wire were used, it would be 1/60th the length of copper for the same
gauge, or 93 feet. This resistance wire can be wound in spirals and
made to occupy a very small space. As long as it is connected in
circuit, the energy of the dynamo otherwise consumed as light would be
wasted as heat. This heat could be utilized in the hot water boiler or
stove when the lights were turned off.
In actual practice, however, the resistance necessary to keep the
dynamo up to full load permanently, would not be furnished by one set
of resistance coils. Each lamp circuit would have a set of resistance
coils of its own. A double-throw switch would turn off the lamps and
turn on the resistance coils, or _vice versa_.
Let us say a lamp circuit consisted of 6 carbon lamps, of 16
candlepower each. It would consume 6 × 1/2 ampere, or 3 amperes of
current, and interpose a resistance of 36.6 ohms--say 37 ohms. Three
amperes would require a wire of at least 1,500 circular mills in area
for safety. This corresponds to a No. 18 wire. A No. 18 copper wire
interposes a resistance of one ohm, for each 156.5 feet length. For 37
ohms, 5,790 feet would be required, for copper wire, which of course
would be impractical. Dividing by 30 gives 193 feet for 30% German
silver wire; and dividing by 60 gives 96 feet of nichrome wire of the
same gauge.
It is simple to figure each circuit in this way and to construct
resistance units for each switch. Since the resistance units develop
considerable heat, they must be enclosed and protected.
_A Home-made Stove or Radiator_
While we are on the subject of resistance coils it might be well here
to describe how to make stoves for cooking, and radiators for heating
the house, at small expense. These stoves consist merely of
resistances which turn hot--a dull red--when the current is turned on.
Iron wire, German silver wire, or the various trade brands of
resistance wire, of which nichrome, calido, and manganin are samples,
can be used. In buying this wire, procure the table of resistance and
carrying capacity from the manufacturers. From this table you can make
your own radiators to keep the house warm in winter. Iron wire has the
disadvantage of oxidizing when heated to redness, so that it goes to
pieces after prolonged use. It is cheap, however, and much used for
resistance in electrical work.
Let us say we wish to heat a bathroom, a room 6 × 8, and 8 feet
high--that is a room containing 384 cubic feet of air space. Allowing
2 watts for each cubic foot, we would require 768 watts of current, or
practically 7 amperes at 110 volts. What resistance would be required
to limit the current to this amount? Apply Ohm's Law, as before, and
we have R equals E divided by C, or R equals 110 divided by 7, which
is 15.7 ohms. Forty-two feet of No. 20 German silver wire would emit
this amount of heat and limit the current output to 7 amperes. In the
Far West, it is quite common, in the outlying district, to find
electric radiators made out of iron pipe covered with asbestos, on
which the requisite amount of iron wire is wound and made secure. This
pipe is mounted in a metal frame. Or the frame may consist of two
pipes containing heating elements; and a switch, in this case, is so
arranged that either one or two heating elements may be used at one
time, according to the weather. An ingenious mechanic can construct
such a radiator, experimenting with the aid of an ammeter to ascertain
the length of wire required for any given stove.
_Regulating Voltage at Switchboards_
The voltage of any given machine may be regulated, within wide limits,
by means of the field rheostat on the switchboard.
A dynamo with a rated speed of 1,500 revolutions per minute, for 110
volts, will actually attain this voltage at as low as 1,200 r.p.m. if
all the regulating resistance be cut out. You can test this fact with
your own machine by cutting out the resistance from the shunt field
entirely, and starting the machine slowly, increasing its speed
gradually, until the voltmeter needle registers 110 volts. Then
measure the speed. It will be far below the rated speed of your
machine.
If, on the other hand, the speed of such a machine runs up to 2,500 or
over--that is, an excess of 67%--the voltage would rise
proportionally, unless extra resistance was cut in. By cutting in such
resistance--by the simple expedient of turning the rheostat handle on
the switchboard,--the field coils are so weakened that the voltage is
kept at the desired point in spite of the excessive speed of the
machine. Excessive speeds are to be avoided, as a rule, because of
mechanical strain. But within a wide range, the switchboard rheostat
can be used for voltage regulation.
As it would be a source of continual annoyance to have to run to the
switchboard every time the load of the machine was varied greatly this
plan would not be practical for the isolated plant, unless the
rheostat could be installed,--with a voltmeter--in one's kitchen.
This could be done simply by running a small third wire from the
switchboard to the house. Then, when the lights became dim from
excessive load, a turn of the handle would bring them back to the
proper voltage; and when they flared up and burned too bright, a turn
of the handle in the opposite direction would remedy matters. By this
simple arrangement, any member of the family could attend to voltage
regulation with a minimum of bother.
_Automatic Devices_
There are several automatic devices for voltage regulation at the
switchboard on the market. These consist usually of vibrator magnets
or solenoids, in which the strength of the current, varying with
different speeds, reacts in such a way as to regulate field
resistance. Such voltage regulators can be had for $40 or less, and
are thoroughly reliable.
* * * * *
To sum up the discussion of governors and voltage regulators: If you
can allow a liberal proportion of water-power, and avoid crowding
your dynamo, the chances are you will not need a governor for the
ordinary reaction turbine wheel. Start your plant, and let it run for
a few days or a few weeks without a governor, or regulator. Then if
you find the operation is unsatisfactory, decide for yourself which of
the above systems is best adapted for your conditions. Economy as well
as convenience will affect your decision. The plant which is most
nearly automatic is the best; but by taking a little trouble and
giving extra attention, a great many dollars may be saved in extras.
_Starting the Dynamo_
You are now ready to put your plant in operation. Your dynamo has been
mounted on a wooden foundation, and belted to the countershaft, by
means of an endless belt.
See that the oil cups are filled. Then throw off the main switch and
the field switch at the switchboard; open the water gate slowly, and
occasionally test the speed of the dynamo. When it comes up to rated
speed, say 1,500 per minute, let it run for a few minutes, to be sure
everything is all right.
Having assured yourself that the mechanical details are all right, now
look at the voltmeter. It is probably indicating a few volts pressure,
from 4 to 8 or 10 perhaps. This pressure is due to the residual
magnetism in the field cores, as the field coils are not yet
connected. If by any chance, the needle does not register, or is now
back of 0, try changing about the connections or the voltmeter on the
back of the switchboard.
Now snap on the field switch. Instantly the needle will begin to move
forward, though slowly; and it will stop. Turn the rheostat handle
gradually; as you advance it, the voltmeter needle will advance.
Finally you will come to a point where the needle will indicate 110
volts.
If you have designed your transmission line for a drop of 5 volts at
half-load, advance the rheostat handle still further, until the
needle points to 115 volts. Let the machine run this way for some
time. When assured all is right, throw on the main switch, and turn on
the light at the switchboard. Then go to the house and gradually turn
on lights. Come back and inspect the dynamo as the load increases. It
should not run hot, nor even very warm, up to full load. Its brushes
should not spark, though a little sparking will do no harm.
Your plant is now ready to deliver current up to the capacity of its
fuses. See that it does not lack good lubricating oil, and do not let
its commutator get dirty. The commutator should assume a glossy
chocolate brown color. If it becomes dirty, or the brushes spark
badly, hold a piece of fine sandpaper against it. Never use emery
paper! If, after years of service, it becomes roughened by wear, have
it turned down in a lathe. Occasionally, every few weeks, say, take
the brushes out and clean them with a cloth. They will wear out in the
course of time and can be replaced for a few cents each. The bearings
may need replacing after several years' continuous use.
Otherwise your electric plant will take care of itself. Keep it up to
speed, and keep it clean and well oiled. Never shut it down unless you
have to. In practice, dynamos run week after week, year after year,
without stopping. This one, so long as you keep it running true to
form, will deliver light, heat and power to you for nothing, which
your city cousin pays for at the rate of 10 cents a kilowatt-hour.
PART III
GASOLINE ENGINES, WINDMILLS, ETC. THE STORAGE BATTERIES
CHAPTER X
GASOLINE ENGINE PLANTS
The standard voltage set--Two-cycle and four-cycle gasoline
engines--Horsepower, and fuel consumption--Efficiency of small
engines and generators--Cost of operating a one-kilowatt plant.
Electricity is of so much value in farm operations, as well as in the
farm house, that the farmer who is not fortunate enough to possess
water-power of his own, or to live in a community where a coöperative
hydro-electric plant may be established, should not deny himself its
many conveniences. In place of the water wheel to turn the dynamo,
there is the gasoline engine (or other forms of internal combustion
engine using oil, gas, or alcohol as fuel); in many districts where
steam engines are used for logging or other operations, electricity
may be generated as a by-product; and almost any windmill capable of
pumping water can be made to generate enough electricity for lighting
the farm house at small expense.
The great advantage of water-power is that the expense of
maintenance--once the plant is installed--is practically nothing. This
advantage is offset in some measure by the fact that other forms of
power, gas, steam, or windmills, are already installed, in many
instances and that their judicious use in generating electricity does
not impair their usefulness for the other farm operations for which
they were originally purchased. In recent years gasoline engines have
come into general use on farms as a cheap dependable source of power
for all operations; and windmills date from the earliest times. They
may be installed and maintained cheaply, solely for generating
electricity, if desired. Steam engines, however, require so much care
and expert attention that their use for farm electric plants is not to
be advised, except under conditions where a small portion of their
power can be used to make electricity as a by-product.
There are two types of gasoline engine electric plants suitable for
the farm, in general use:
First: The Standard Voltage Set, in which the engine and dynamo are
mounted on one base, and the engine is kept running when current is
required for any purpose. These sets are usually of the 110-volt type,
and all standard appliances, such as irons, toasters, motors, etc.,
may be used in connection with them. Since the electricity is drawn
directly from the dynamo itself, without a storage battery, it is
necessary that these engines be efficient and governed as to speed
within a five per cent variation from no load to full load.
Second: Storage Battery Sets, in which the dynamo is run only a few
hours each week, and the electricity thus generated is "stored" by
chemical means, in storage batteries, for use when required. Since, in
this case, the current is drawn from the battery, instead of the
dynamo, when used for lighting or other purposes, it is not necessary
that a special type of engine be used to insure constant speed.
_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.
With gasoline power, the cost of the engine offsets the cost of the
water wheel. The engine is more expensive than the ordinary gasoline
engine; but even this item of cost is offset by the cost of labor and
materials used in installing a water wheel.
The expense of maintenance is limited to gasoline and oil.
Depreciation enters in both cases; and though it may be more rapid
with a gasoline engine than a water wheel, that item will not be
considered here. The cost of lubricating oil is inconsiderable. It
will require, when operated at from one-half load to full load,
approximately one pint of gasoline to each horsepower hour. When
operated at less than half-load, its efficiency lowers. Thus, for a
quarter-load, an average engine of this type may require three pints
of gasoline for each horsepower hour. For this reason it is well, in
installing such a plant, to have it of such size that it will be
operating on at least three-fourths load under normal draft of
current. Norman H. Schneider, in his book "Low Voltage Electric
Lighting," gives the following table of proportions between the engine
and dynamo:
Actual watts Actual Horsepower Nearest engine size
150 .5 1/2
225 .7 3/4
300 .86 1
450 1.12 1-1/4
600 1.5 1-1/2
750 1.7 1-3/4
1000 2.3 2-1/2
2000 4.5 5
4000 9.0 10
This table is figured for an efficiency of only 40 per cent for the
smaller generators, and 60 per cent for the larger. In machines from 5
to 25 kilowatts, the efficiency will run considerably higher.
To determine the expense of operating a one-kilowatt gasoline
generator set of this type, as to gasoline consumption, we can assume
at full load that the gasoline engine is delivering 2-1/2 horsepower,
and consuming, let us say, 1-1/4 pint of gasoline for each horsepower
hour (to make allowance for lower efficiency in small engines). That
would be 3.125 pints of gasoline per hour. Allowing a ten per cent
loss of current in wiring, we have 900 watts of electricity to use,
for this expenditure of gasoline. This would light 900 ÷ 25 = 36 lamps
of 25 watts each, a liberal allowance for house and barn, and
permitting the use of small cooking devices and other conveniences
when part of the lights were not in use. With gasoline selling at 12
cents a gallon, the use of this plant for an hour at full capacity
would cost $0.047. Your city cousin pays 9 cents for the same current
on a basis of 10 cents per kilowatt-hour; and in smaller towns where
the rate is 15 cents, he would pay 13-1/2 cents.
Running this plant at only half-load--that is, using only 18 lights,
or their equivalent--would reduce the price to about 3 cents an
hour--since the efficiency decreases with smaller load. It is
customary to figure an average of 3-1/2 hours a day throughout the
year, for all lights. On this basis the cost of gasoline for this
one-kilowatt plant would be 16-1/2 cents a day for full load, and
approximately 10-1/2 cents a day for half-load. This is extremely
favorable, as compared with the cost of electric current in our cities
and towns, at the commercial rate, especially when one considers that
light and power are to be had at any place or at any time on the farm
simply by starting the engine. A smaller plant, operating at less cost
for fuel, would furnish ample light for most farms; but it is well to
remember in this connection plants smaller than one kilowatt are
practical for light only, since electric irons, toasters, etc., draw
from 400 to 660 watts each. Obviously a plant of 300 watts capacity
would not permit the use of these instruments, although it would
furnish 10 or 12 lamps of 25 watts each.
CHAPTER XI
THE STORAGE BATTERY
What a storage battery does--The lead battery and the Edison
battery--Economy of tungsten lamps for storage batteries--The
low-voltage battery for electric light--How to figure the capacity
of a battery--Table of light requirements for a farm
house--Watt-hours and lamp-hours--The cost of storage battery
current--How to charge a storage battery--Care of storage
batteries.
For the man who has a small supply of water to run a water wheel a few
hours at a time, or who wishes to store electricity while he is doing
routine jobs with a gasoline engine or other source of power, the
storage battery solves the problem. The storage battery may be likened
to a tank of water which is drawn on when water is needed, and which
must be re-filled when empty. A storage battery, or accumulator is a
device in which a chemical action is set up when an electric current
is passed through it. This is called _charging_. When such a battery
is charged, it has the property of giving off an electric current by
means of a reversed chemical action when a circuit is provided,
through a lamp or other connection. This reversed action is called
_discharging_. Such a battery will discharge nearly as much current as
is required originally to bring about the first chemical action.
There are two common types of storage battery--the lead accumulator,
made up of lead plates (alternately positive and negative); and the
two-metal accumulator, of which the Edison battery is a
representative, made up of alternate plates of iron and nickel. In the
lead accumulator, the "positive" plate may be recognized by its brown
color when charging, while the "negative" plate is usually light gray,
or leaden in color. The action of the charging current is to form
oxides of lead in the plates; the action of the discharging current is
to reduce the oxides to metallic lead again. This process can be
repeated over and over again during the life of the battery.
Because of the cost of the batteries themselves, it is possible (from
the viewpoint of the farmer and the size of his pocketbook) to store
only a relatively small amount of electric current. For this reason,
the storage battery was little used for private plants, where expense
is a considerable item, up to a few years ago. Carbon lamps require
from 3-1/2 to 4 watts for each candlepower of light they give out; and
a lead battery capable of storing enough electricity to supply the
average farm house with light by means of carbon lamps for three or
four days at a time without recharging, proved too costly for private
use.
_The Tungsten Lamp_
With the advent of the new tungsten lamp, however, reducing the
current requirements for light by two-thirds, the storage battery
immediately came into its own, and is now of general use.
Since incandescent lamps were first invented scientists have been
trying to find some metal of high fusion to use in place of the carbon
filament of the ordinary lamp. The higher the fusing point of this
filament of wire, the more economical would be the light. Edison
sought, thirty years ago, for just the qualities now found in tungsten
metal. Tungsten metal was first used for incandescent lamps in the
form of a paste, squirted into the shape of a thread. This proved too
fragile. Later investigators devised means of drawing tungsten into
wire; and it is tungsten wire that is now used so generally in
lighting. A tungsten lamp has an average efficiency of 1-1/4 watts per
candlepower, compared with 3-1/2 to 4 watts of the old-style carbon
lamp. In larger sizes the efficiency is as low as .9 watt per
candlepower; and only recently it has been found that if inert
nitrogen gas is used in the glass bulb, instead of using a high vacuum
as is the general practice, the efficiency of the lamp becomes still
higher, approaching .5 watt for each candlepower in large lamps. This
new nitrogen lamp is not yet being manufactured in small domestic
sizes, though it will undoubtedly be put on the market in those sizes
in the near future.
[Illustration: The Fairbanks Morse oil engine storage battery set]
The tungsten lamp, requiring only one-third as much electric current
as the carbon lamp, for the same amount of light, reduces the size
(and the cost) of the storage battery in the same degree, thus
bringing the storage battery within the means of the farmer. Some idea
of the power that may be put into a small storage battery is to be had
from the fact that a storage battery of only 6 volts pressure, such as
is used in self-starters on automobiles, will turn a motor and crank a
heavy six-cylinder engine; or it will run the automobile, without
gasoline, for a mile or more with its own accumulated store of
electric current.
_The Low Voltage Battery_
The 30-volt storage battery has become standard for small lighting
plants, since the introduction of the tungsten lamp. Although the
voltage of each separate cell of this battery registers 2.5 volts when
fully charged, it falls to approximately 2 volts per cell immediately
discharging begins. For this reason, it is customary to figure the
working pressure of each cell at 2 volts. This means that a 30-volt
battery should consist of at least 15 cells. Since, however, the
voltage falls below 2 for each cell, as discharging proceeds, it is
usual to include one additional cell for regulating purposes. Thus,
the ordinary 30-volt storage battery consists of 16 cells, the last
cell in the line remaining idle until the lamps begin to dim, when it
is switched in by means of a simple arrangement of connections. This
maintains a uniform pressure of 30 volts from the beginning to the end
of the charge, at the lamp socket.
We saw in earlier chapters that the 110-volt current is the most
satisfactory, under all conditions, where the current is to be used
for heating and small power, as well as light. But a storage battery
of 110 volts would require at least 55 cells, which would make it too
expensive for ordinary farm use. As a 30-volt current is just as
satisfactory for electric light, this type has become established, in
connection with the battery, and it is used for electric lighting
only, as a general rule.
Batteries are rated first, as to voltage; second, as to their capacity
in ampere hours--that is, the number of amperes that may be drawn from
them in a given number of hours. Thus, a battery rated at 60 ampere
hours would give 60 amperes, at 30 volts pressure, for one hour; 30
amperes for 2 hours; 15 amperes for 4 hours; 7-1/2 amperes for 8
hours; 3-3/4 amperes for 16 hours; etc., etc. In practice, a battery
should not be discharged faster than its 8-hour rate. Thus, a
60-ampere hour battery should not be drawn on at a greater rate than
7-1/2 amperes per hour.
This 8-hour rate also determines the rate at which a battery should
be re-charged, once it is exhausted. Thus, this battery should be
charged at the rate of 7-1/2 amperes for 8 hours, with another hour
added to make up for losses that are bound to occur. A battery of
120-ampere hour capacity should be charged for 8 or 9 hours at the
rate of 120 ÷ 8, or 15 amperes, etc.
To determine the size of battery necessary for any particular
instance, it is necessary first to decide on the number of lamps
required, and their capacity. Thirty-volt lamps are to be had in the
market in sizes of 10, 15 and 20 watts; they yield respectively 8, 12,
and 16 candlepower each. Of these the 20-watt lamp is the most
satisfactory for the living rooms; lamps of 10 or 15 watts may be used
for the halls, the bathroom and the bedrooms. At 30 volts pressure
these lamps would require a current of the following density in
amperes:
Candle
Power 30-volt lamp Amperes
8 10 watts 0.33
12 15 watts 0.50
16 20 watts 0.67
Let us assume, as an example, that Farmer Brown will use 20-watt
lamps in his kitchen, dining room, and sitting room; and 10-watt lamps
in the halls, bathroom, and bedrooms. His requirements may be figured
either in lamp hours or in watt-hours. Since he is using two sizes of
lamps, it will be simpler to figure his requirements in watt-hours.
Thus:
Number Size of Hours Watt-
Room of lamps lamps burned hours
Kitchen 1 20 4 80
Dining room 2 20 2 80
Sitting room 3 20 4 240
(3) Bedrooms 1 (each) 10 1 30
Bathroom 1 10 2 20
(2) Halls 1 (each) 10 4 80
Pantry 1 10 1 10
Cellar 1 10 1 10
----
Total 550
Since amperes equal watts divided by volts, the number of ampere hours
required in this case each night would be 550 ÷ 30 = 18.3 ampere
hours; or approximately 4-1/2 amperes per hour for 4 hours.
Say it is convenient to charge this battery every fourth day. This
would require a battery of 4 × 18.3 ampere hours, or 73.2 ampere
hours. The nearest size on the market is the 80-ampere hour battery,
which would be the one to use for this installation.
To charge this battery would require a dynamo capable of delivering 10
amperes of current for 9 hours. The generator should be of 45 volts
pressure (allowing 2-1/2 volts in the generator for each 2 volts of
battery) and the capacity of the generator would therefore be 450
watts. This would require a 1-1/4 horsepower gasoline engine. At 1-1/4
pints of gasoline for each horsepower, nine hours work of this engine
would consume 14 pints of gasoline--or say 16 pints, or two gallons.
At 12 cents a gallon for gasoline, lighting your house with this
battery would cost 24 cents for four days, or 6 cents a day. Your city
cousin, using commercial current, would pay 5-1/2 cents a day for the
same amount of current at 10 cents a kilowatt-hour; or 8-1/4 cents at
a 15-cent rate. If the battery is charged by the farm gasoline engine
at the same time it is doing its other work, the cost would be still
less, as the extra gasoline required would be small.
This figure does not take into account depreciation of battery and
engine. The average farmer is too apt to overlook this factor in
figuring the cost of machinery of all kinds, and for that reason is
unprepared when the time comes to replace worn-out machinery. The
dynamo and switchboard should last a lifetime with ordinary care, so
there is no depreciation charge against them. The storage battery, a
30-volt, 80-ampere hour installation, should not cost in excess of
$100; and, if it is necessary to buy a gasoline engine, a 1-1/4
horsepower engine can be had for $50 or less according to the type.
Storage batteries of the lead type are sold under a two-years'
guarantee--which does not mean that their life is limited to that
length of time. With good care they may last as long as 10 years; with
poor care it may be necessary to throw them away at the end of a year.
The engine should be serviceable for at least 10 years, with ordinary
replacements; and the storage battery may last from 6 to 10 years,
with occasional renewal of parts. If it were necessary to duplicate
both at the end of ten years, this would make a carrying charge of
$1.25 a month for depreciation, which must be added to the cost of
light.
_Figuring by Lamp Hours_
If all the lamps are to be of the same size--either ten, fifteen, or
twenty watts, the light requirements of a farm house can be figured
readily by lamp hours. In that event, the foregoing table would read
as follows:
Lamp hours
Kitchen, 1 lamp, 4 hours 4
Sitting room, 3 lamps, 4 hours each 12
Dining room, 2 lamps, 2 hours each 4
Bedrooms, 3 lamps, 1 hour each 3
Halls, 2 lamps, 4 hours each 8
Bathroom, 1 lamp, 2 hours 2
Pantry and cellar, 2 lamps, 1 hour each 2
To determine the ampere hours from this table, multiply the total
number of lamp hours by the current in amperes required for each lamp.
As 10, 15, and 20-watt tungsten lamps require .33, .50 and .67
amperes, respectively at 30 volts pressure, the above requirements in
ampere hours would be 12, 17-1/2, or 24 ampere hours, according to the
size of lamp chosen. This gives the average current consumption for
one night. If it is desired to charge the battery twice a week on the
average, multiply the number of lamp hours by 4, to get the size of
battery required.
The foregoing illustration is not intended to indicate average light
requirements for farms, but is given merely to show how a farmer may
figure his own requirements. In some instances, it will be necessary
to install a battery of 120 or more ampere hours, whereas a battery of
40 or 60 ampere hours would be quite serviceable in other instances.
It all depends on how much light you wish to use and are willing to
pay for, because with a storage battery the cost of electric light is
directly in proportion to the number of lights used.
As a general rule, a larger generator and engine are required for a
larger battery--although it is possible to charge a large battery
with a small generator and engine by taking more time for the
operation.
_How to Charge a Storage Battery_
Direct current only can be used for charging storage batteries. In the
rare instance of alternating current only being available, it must be
converted into direct current by any one of the many mechanical,
chemical, or electrical devices on the market--that is, the
alternating current must be straightened out, to flow always in one
direction.
A shunt-wound dynamo must be used; else, when the voltage of the
battery rises too high, it may "back up" and turn the dynamo as a
motor, causing considerable damage. If a compound dynamo is already
installed, or if it is desired to use such a machine for charging
storage batteries, it can be done simply by disconnecting the series
windings on the field coils, thus turning the machine into a shunt
dynamo.
The voltage of the dynamo should be approximately 50 per cent above
the working pressure of the battery. For this reason 45-volt machines
are usually used for 30 or 32-volt batteries. Higher voltages may be
used, if convenient. Thus a 110-volt dynamo may be used to charge a
single 2-volt cell if necessary, although it is not advisable.
_Direction of Current_
Electricity flows from the positive to the negative terminal. A
charging current must be so connected that the negative wire of the
dynamo is always connected to the negative terminal of the battery,
and the positive wire to the positive terminal. As the polarity is
always marked on the battery, there is little danger of making a
mistake in this particular.
When the storage battery is charged, and one begins to use its
accumulation of energy, the current comes out in the opposite
direction from which it entered in charging. In this respect, a
storage battery is like a clock spring, which is wound up in one
direction, and unwinds itself in the other. With all storage battery
outfits, an ammeter (or current measure) is supplied with zero at the
center. When the battery is being charged, the indicating needle
points in one direction in proportion to the strength of the current
flowing in; and when the battery is being discharged, the needle
points in the opposite direction, in proportion to the strength of the
current flowing out.
Sometimes one is at loss, in setting about to connect a battery and
generator, to know which is the positive and which the negative wire
of the generator. A very simple test is as follows:
Start the generator and bring it up to speed. Connect some form of
resistance in "series" with the mains. A lamp in an ordinary lamp
socket will do very well for this resistance. Dip the two ends of the
wire (one coming from the generator, the other through the lamp) into
a cup of water, in which a pinch of salt is dissolved. Bring them
almost together and hold them there. Almost instantly, one wire will
begin to turn bright, and give off bubbles. The wire which turns
bright and gives off bubbles is the _negative_ wire. The other is the
positive.
[Illustration: A rough-and-ready farm electric plant, supplying two
farms with light, heat and power; and a Ward Leonard-type
circuit-breaker for charging storage batteries]
_Care of Battery_
Since specific directions are furnished with all storage batteries, it
is not necessary to go into the details of their care here. Storage
battery plants are usually shipped with all connections made, or
plainly indicated. All that is necessary is to fill the batteries with
the acid solution, according to directions, and start the engine. If
the engine is fitted with a governor, and the switchboard is of the
automatic type, all the care necessary in charging is to start the
engine. In fact, many makes utilize the dynamo as a "self-starter" for
the engine, so that all that is necessary to start charging is to
throw a switch which starts the engine. When the battery is fully
charged, the engine is stopped automatically.
The "electrolyte" or solution in which the plates of the lead battery
are immersed, is sulphuric acid, diluted with water in the proportion
of one part of acid to five of water, by volume.
The specific gravity of ordinary commercial sulphuric acid is 1.835.
Since its strength is apt to vary, however, it is best to mix the
electrolyte with the aid of the hydrometer furnished with the battery.
The hydrometer is a sealed glass tube, with a graduated scale somewhat
resembling a thermometer. The height at which it floats in any given
solution depends on the density of the solution. It should indicate
approximately 1.15 for a storage battery electrolyte before charging.
It should not be over 1.15--or 1,150 if your hydrometer reads in
thousandths.
Only pure water should be used. Distilled water is the best, but fresh
clean rain water is permissible. Never under any circumstances use
hydrant water, as it contains impurities which will injure the
battery, probably put it out of commission before its first charge.
_Pour the acid into the water._ Never under any circumstances pour the
water into the acid, else an explosion may occur from the heat
developed. Mix the electrolyte in a stone crock, or glass container,
stirring with a glass rod, and testing from time to time with a
hydrometer. Let it stand until cool and then pour it into the battery
jars, filling them to 1/2 inch above the top of the plates.
Then begin charging. The first charge will probably take a longer time
than subsequent charges. If the installation is of the automatic type,
all that is necessary is to start the engine. If it is not of the
automatic type, proceed as follows:
First be sure all connections are right. Then start the engine and
bring the dynamo up to its rated speed. Adjust the voltage to the
pressure specified. Then throw the switch connecting generator to
battery. Watch the ammeter. It should register in amperes, one-eighth
of the ampere-hour capacity of the battery, as already explained. If
it registers too high, reduce the voltage of the generator slightly,
by means of the field rheostat connected to the generator. This will
also reduce the amperes flowing. If too low, raise the voltage until
the amperes register correctly. Continue the charging operation until
the cells begin to give off gas freely; or until the specific gravity
of the electrolyte, measured by the hydrometer, stands at 1.24. Your
battery is now fully charged. Throw the switch over to the service
line, and your accumulator is ready to furnish light if you turn on
your lamps.
Occasionally add distilled water to the cells, to make up for
evaporation. It is seldom necessary to add acid, as this does not
evaporate. If the battery is kept fully charged, it will not freeze
even when the thermometer is well below zero.
A storage battery should be installed as near the house as
possible--in the house, if possible. Since its current capacity is
small, transmission losses must be reduced to a minimum.
In wiring the house for storage battery service, the same rules apply
as with standard voltage. Not more than 6 amperes should be used on
any single branch circuit. With low voltage batteries (from 12 volts
to 32 volts) it is well to use No. 10 or No. 12 B. & S. gauge
rubber-covered wire, instead of the usual No. 14 used with standard
voltage. The extra expense will be only a few cents for each circuit,
and precious volts will be saved in distribution of the current.
CHAPTER XII
BATTERY CHARGING DEVICES
The automatic plant most desirable--How an automobile lighting and
starting system works--How the same results can be achieved in
house lighting, by means of automatic devices--Plants without
automatic regulation--Care necessary--The use of heating devices on
storage battery current--Portable batteries--An electricity
"route"--Automobile power for lighting a few lamps.
The water-power electric plants described in preceding chapters are
practically automatic in operation. This is very desirable, as such
plants require the minimum of care. It is possible to attain this same
end with a storage battery plant.
Automatic maintenance approaches a high degree of perfection in the
electric starting and lighting device on a modern automobile. In this
case, a small dynamo geared to the main shaft is running whenever the
engine is running. It is always ready to "pump" electricity into the
storage battery when needed. An electric magnet, wound in a peculiar
manner, automatically cuts off the charging current from the dynamo,
when the battery is "full;" and the same magnet, or "regulator,"
permits the current to flow into the battery when needed. The
principle is the same as in the familiar plumbing trap, which
constantly maintains a given level of water in a tank, no matter how
much water may be drawn from the tank. The result, in the case of the
automobile battery, is that the battery is always kept fully charged;
for no sooner does the "level" of electricity begin to drop (when used
for starting or lighting) than the generator begins to charge. This is
very desirable in more ways than one. In the first place, the energy
of the battery is always the same; and in the second place, the mere
fact that the battery is always kept fully charged gives it a long
life.
The same result can be achieved in storage battery plants for house
lighting, where the source of power is a gasoline or other engine
engaged normally in other work. Then your electric current becomes
merely a by-product of some other operation.
Take a typical instance where such a plant would be feasible: Farmer
Brown has a five horsepower gasoline engine--an ordinary farm engine
for which he paid probably $75 or $100. Electric light furnished
direct from such an engine would be intolerable because of its
constant flickering. This five horsepower engine is installed in the
milk room of the dairy, and is belted to a countershaft. This
countershaft is belted to the vacuum pump for the milking machine, and
to the separator, and to a water pump, any one of which may be thrown
into service by means of a tight-and-loose pulley. This countershaft
is also belted to a small dynamo, which runs whenever the engine is
running. The milking machine, the separator, and the water pump
require that the gasoline engine be run on the average three hours
each day.
The dynamo is connected by wires to the house storage battery through
a properly designed switchboard. The "brains" of this switchboard is
a little automatic device (called a regulator or a circuit breaker),
which opens and shuts according to the amount of current stored in the
battery and the strength of the current from the generator. When the
battery is "full," this regulator is "open" and permits no current to
flow. Then the dynamo is running idle, and the amount of power it
absorbs from the gasoline engine is negligible. When the "level" of
electricity in the battery falls, due to drawing current for light,
the regulator is "shut," that is, the dynamo and battery are
connected, and current flows into the battery.
These automatic instruments go still farther in their brainy work.
They do not permit the dynamo to charge the battery when the voltage
falls below a fixed point, due to the engine slowing down; neither do
they permit the dynamo current to flow when the voltage gets too high
due to sudden speeding up of the engine.
Necessarily, an instrument which will take care of a battery in this
way, is intricate in construction. That is not an argument against it
however. A watch is intricate, but so long as we continue to wind it
at stated intervals, it keeps time. So with this storage battery
plant: so long as Farmer Brown starts his engine to do his farm chores
every day, his by-product of electricity is stored automatically.
Such installations are not expensive. A storage battery capable of
lighting 8 tungsten lamps, of 16 candlepower each, continuously for 8
hours (or fewer lamps for a longer time); a switchboard containing all
the required regulating instruments; and a dynamo of suitable size,
can be had for from $250 to $300. All that is necessary to put such a
plant in operation, is to belt the dynamo to the gasoline engine so
that it will run at proper speed; and to connect the wires from dynamo
to switchboard, and thence to the house service. The dynamo required
for the above plant delivers 10 amperes at 45 volts pressure, or 10 ×
45 = 450 watts. A gasoline, gas, or oil engine, or a windmill of
1-1/2 horsepower furnishes all the power needed. If the farmer uses
his engine daily, or every other day, for other purposes, the cost of
power will be practically negligible. With this system electric lights
are available at any time day or night; and when the gasoline engine
is in service daily for routine farm chores, the battery will never
run low.
This system is especially desirable where one uses a windmill for
power. The speed of the windmill is constantly fluctuating, so much so
in fact that it could not be used for electric light without a storage
battery. But when equipped with a regulator on the switchboard which
permits the current to flow only when the battery needs it, and then
only when the speed of the windmill is correct, the problem of turning
wind power into electric light is solved.
* * * * *
If the farmer does not desire to go to the additional expense of
automatic regulation, there are cheaper plants, requiring attention
for charging. These plants are identical with those described above,
except they have no regulators. With these plants, when the battery
runs low (as is indicated by dimming of the lights) it is necessary to
start the engine, bring it up to speed, adjust the dynamo voltage to
the proper pressure, and throw a switch to charge the battery. For
such plants it is customary to run the engine to charge the battery
twice a week. It is necessary to run the engine from 8 to 10 hours to
fully charge the discharged battery. When the battery approaches full
charge, the fact is evidenced by so-called "gassing" or giving off of
bubbles. Another way to determine if the battery is fully charged is
by means of the voltmeter, as the volts slowly rise to the proper
point during the process of charging. A third way, and probably the
most reliable is by the use of the hydrometer. The voltage of each
cell when fully charged should be 2.5; it should never be discharged
below 1.75 volts. Many storage battery electric light plants on the
market are provided with a simple and inexpensive circuit breaker,
which automatically cuts off the current and stops the engine when the
battery is charged. The current is then thrown from the dynamo to the
house service by an automatic switch. If such a circuit breaker is not
included, it is necessary to throw the switch by hand when charging is
begun or ended.
Since the principal item of first cost, as well as depreciation, in a
storage battery electric light plant is the storage battery itself,
the smallest battery commensurate with needs is selected. Since the
amount of current stored by these batteries is relatively small,
electric irons and heating devices such as may be used freely on a
direct-connected plant without a battery, are rather expensive
luxuries. For instance, an electric iron drawing 400 watts an hour
while in use, requires as much energy as 20 tungsten lamps of 16
candlepower each burning for the same length of time. Its rate of
current consumption would be over 13 amperes, at 30 volts; which would
require a larger battery than needed for light in the average farm
home.
The use to which electricity from a storage battery is put, however,
is wholly a matter of expense involved; and if one is willing to pay
for these rather expensive luxuries, there is no reason why he should
not have them. Heating, in any form, by electricity, requires a large
amount of current proportionally. As a matter of fact, there is less
heat to be had in thermal units from a horsepower-hour of electricity
than from three ounces of coal. When one is generating current from
water-power, or even direct from gasoline or oil, this is not an
argument against electric heating devices. But it becomes a very
serious consideration when one is installing a storage battery as the
source of current, because of the high initial cost, and depreciation
of such a battery.
Farmers who limit the use of their storage battery plants to lighting
will get the best service.
_Portable Batteries_
Abroad it is becoming quite common for power companies to deliver
storage batteries fully charged, and call for them when discharged.
Without a stretch of the imagination, we can imagine an ingenious
farmer possessing a water-power electric plant building up a thriving
business among his less fortunate neighbors, with an "electricity"
route. It could be made quite as paying as a milk route.
[Illustration: Connections for charging storage batteries on 110-volt
mains]
Many communities have water or steam power at a distance too great to
transmit 110-volt current by wire economically; and because of lack of
expert supervision, they do not care to risk using current at a
pressure of 500 volts or higher, because of its danger to human life.
In such a case it would be quite feasible for families to wire their
houses, and carry their batteries to the generating plant two or
three times a week to be charged. There are a number of portable
batteries on the market suitable for such service, at voltages ranging
from 6 to 32 volts. The best results would be obtained by having two
batteries, leaving one to be charged while the other was in use; and
if the generating station was located at the creamery or feed mill,
where the farmer calls regularly, the trouble would be reduced to a
minimum.
Such a battery would necessarily be small, and of the sealed type,
similar to those used in automobiles. It could be used merely for
reading lamps--or it could be used for general lighting, according to
the expense the farmer is willing to incur for batteries.
An ordinary storage battery used in automobile ignition and lighting
systems is of the 6-volt, 60-ampere type, called in trade a "6-60."
Lamps can be had for these batteries ranging in sizes from 2
candlepower to 25 candlepower. A lamp of 15 candlepower, drawing 2-1/2
amperes, is used for automobile headlights, and, as any one knows
after an experience of meeting a headlight on a dark road, they give a
great deal of light. A "6-60" battery keeps one of these lamps running
for 24 hours, or two lamps running 12 hours. A minimum of wiring would
be required to install such a battery for the reading lights in the
sitting room, and for a hanging light in the dining room. The
customary gates for charging these batteries in a large city is 10
cents; but in a country plant it could be made less.
To charge such a battery on a 110-volt direct current, it is necessary
to install some means of limiting the amount of current, or in other
words, the charging rate. This charging rate, for 8 hours should be,
as we have seen, one-eighth of the ampere-hour capacity of the
battery. Thus a "6-60" battery would require a 7-1/2 ampere current.
Connecting two such batteries in "series" (that is, the negative pole
of one battery to the positive pole of the second) would make a
12-volt battery. Ten or twelve such batteries could be connected in
"series," and a 110-volt direct current generator would charge them in
8 hours at a 7-1/2 ampere rate.
The diagram on page 259 shows the connections for charging on a
110-volt circuit.
An ordinary 16-candlepower carbon lamp is of 220 ohms resistance, and
(by Ohm's Law, C equals E divided by R) permits 1/2 ampere of current
to flow. By connecting 15 such lamps across the mains, in parallel,
the required 7-1/2 amperes of current would be flowing from the
generator through the lamps, and back again. Connect the battery in
"series" at any point on either of the two mains, between the lamps
and the generator, being careful to connect the positive end to the
positive pole of the battery, and _vice versa_.
Lamps are the cheapest form of resistance; but in case they are not
available, any other form of resistance can be used. Iron wire wound
in spirals can be used, or any of the many makes of special resistance
wire on the market. First it is necessary to determine the amount of
resistance required.
We have just seen that the charging rate of a 60-ampere hour battery
is 7-1/2 amperes. Applying Ohm's Law here, we find that ohms
resistance equals volts divided by amperes, or R = 110/7.5 = 14.67
ohms. With a 220-volt current, the ohms resistance required in series
with the storage battery of this size would be 29.33 ohms.
_Automobile Power for Lighting_
There are many ingenious ways by which an automobile may be utilized
to furnish electric light for the home. The simplest is to run wires
direct from the storage battery of the self-starting system, to the
house or barn, in such a way that the current may be used for reading
lamps in the sitting room. By a judicious use of the current in this
way, the normal operation of the automobile in the daytime will keep
the battery charged for use of the night lamps, and if care is used,
such a plan should not affect the life of the battery. Care should be
used also, in this regard, not to discharge the battery too low to
prevent its utilizing its function of starting the car when it was
desired to use the car. However, if the battery were discharged below
its starting capacity, by any peradventure, the car could be started
by the old-fashioned cranking method.
Using an automobile lighting system for house lighting implies that
the car be stored in a garage near the house or barn; as this battery
is too low in voltage to permit transmitting the current any distance.
One hundred feet, with liberal sized transmission wires is probably
the limit.
That such a system is feasible is amply proved by an occurrence
recently reported in the daily papers. A doctor summoned to a remote
farm house found that an immediate operation was necessary to save the
patient's life. There was no light available, except a small kerosene
lamp which was worse than nothing. The surgeon took a headlight off
his car, strung a pair of wires through a window, and instantly had at
his command a light of the necessary intensity.
Another manner in which an automobile engine may be used for house
lighting is to let it serve as the charging power of a separate
storage battery. The engine can be belted to the generator, in such a
case, by means of the fly wheel. Or a form of friction drive can be
devised, by means of which the rear wheels (jacked up off the floor)
may supply the necessary motive power. In such a case it would be
necessary to make allowance for the differential in the rear axle, so
that the power developed by the engine would be delivered to the
friction drive.
The following pages contain advertisements of Macmillan books by the
same author or on related subjects.
WATER POWER ENGINEERS
DESIGNERS AND MANUFACTURERS
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[Illustration]
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60 MILL STREET
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THE FARMER OF TOMORROW
_Cloth, 12mo, $1.50_
"A crisp, entertaining, and instructive discussion of the
conditions which have brought about the present agricultural
problem in America."--_Countryside Magazine._
"The book is interestingly written and full of many vital
discussions."--_Annals of the American Academy of Political and
Social Science._
"A popular consideration of the fundamental factors affecting the
business of farming."--_Pacific Rural Press._
"The growing, popular question of farming analyzed from all angles,
with many helpful suggestions."--_Leslie's Weekly._
"Any person of intelligence, alive to the present and future
welfare of his country will find 'The Farmer of Tomorrow,' a book
of absorbing character."--_Times-Star._
THE MACMILLAN COMPANY
Publishers
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New York
Coöperation in Agriculture
By G. HAROLD POWELL
_Cloth, 12mo, $1.50_
"The author has a broad outlook and never fails to suggest that the
economic advantages of coöperation may frequently be quite
subordinate to the general social and community interests which are
fostered through a common undertaking. He writes with the genuine
interest of a man having experience and faith in that of which he
speaks."--_Political Science Quarterly._
"A volume which explains in a lucid way the features of the
existing system and the measures taken by farmers to protect their
interests."--_Journal of the Royal Statistical Society._
"Mr. Powell has not attempted to cover the entire field of
agricultural coöperation, but has confined himself to its more
important phases. His work shows a grasp of the issues involved and
a ripeness of conclusion that comes only from actual contact with
the practical side of coöperation."--_American Economic Review._
"The book is decidedly worth while."--_Farm Life and Agriculture._
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RURAL SCIENCE SERIES
Edited by L. H. BAILEY
_Each volume illustrated. Cloth, 12mo._
A series of practical books for farmers and gardeners, sold as a set
or separately. Each one is the work of a competent specialist, and is
suitable for consultation alike by the amateur or professional tiller
of the soil, the scientist or the student. Illustrations of marked
beauty are freely used, and the books are clearly printed and well
bound.
ON SELECTION OF LAND, ETC.
Isaac P. Roberts' The Farmstead $1 50
T. F. Hunt's How to Choose a Farm 1 75
E. S. Cheyney and J. P. Wentling's The Farm Woodlot 1 50
Glenn W. Herrick's Insects Injurious to the Household 1 75
ON TILLAGE, ETC.
F. H. King's The Soil 1 50
Isaac P. Roberts' The Fertility of the Land 1 50
F. H. King's Irrigation and Drainage 1 50
Edward B. Voorhees' Fertilizers 1 25
Edward B. Voorhees' Forage Crops 1 50
J. A. Widtsoe's Dry Farming 1 50
L. H. Bailey's Principles of Agriculture 1 25
S. M. Tracy's Forage Crops for the South 1 50
ON PLANT DISEASES, ETC.
E. C. Lodeman's The Spraying of Plants 1 25
ON GARDEN-MAKING
L. H. Bailey's Garden-Making 1 50
L. H. Bailey's Vegetable-Gardening 1 50
L. H. Bailey's Forcing Book 1 25
L. H. Bailey's Plant Breeding 2 00
ON FRUIT-GROWING, ETC.
L. H. Bailey's Nursery Book 1 50
L. H. Bailey's Fruit-Growing (New Edition) 1 75
L. H. Bailey's The Pruning Book 1 50
F. W. Card's Bush Fruits 1 50
W. Paddock & O. B. Whipple's Fruit-Growing in Arid Regions 1 50
J. E. Coit's Citrus Fruits _Prepar_
ON THE CARE OF LIVE-STOCK
Nelson S. Mayo's The Diseases of Animals 1 50
W. H. Jordan's The Feeding of Animals 1 50
I. P. Roberts' The Horse 1 25
M. W. Harper's Breaking and Training of Horses 1 75
George C. Watson's Farm Poultry. New edition 1 50
John A. Craig's Sheep Farming 1 50
ON DAIRY WORK, FARM CHEMISTRY, ETC.
Henry H. Wing's Milk and Its Products. New edition 1 50
J. G. Lipman's Bacteria and Country Life 1 50
ON ECONOMICS AND ORGANIZATION
William A. McKeever's Farm Boys and Girls 1 50
I. P. Roberts' The Farmer's Business Handbook 1 25
George T. Fairchild's Rural Wealth and Welfare 1 25
H. N. Ogden's Rural Hygiene 1 50
J. Green's Law for the American Farmer 1 50
G. H. Powell's Coöperation in Agriculture 1 50
THE MACMILLAN COMPANY
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NEW YORK
RURAL TEXT-BOOK SERIES
Edited by L. H. BAILEY
_Each volume illustrated. Cloth, 12mo._
While the RURAL SCIENCE SERIES is designed primarily for popular
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classroom work and for special use in consultation and reference. The
RURAL TEXT-BOOK SERIES is planned to cover eventually the entire range
of public school and college texts.
Duggar, B. M.
Physiology of Plant Production $1 60
Duggar, John Frederick
Southern Field Crops 1 75
Gay, C. Warren
Principles and Practice of Judging Live-Stock 1 50
Harper, M. W.
Animal Husbandry for Schools 1 40
Hitchcock, A. S.
Grasses 1 50
Livingston, George
Field Crop Production 1 40
Lyon, T. L. and Fippin, E. O.
Principles of Soil Management 1 75
Mann, A. R.
Beginnings in Agriculture 75
Montgomery, G. F.
Corn Crops 1 60
Piper, Charles V.
Forage Plants and Their Culture 1 75
Warren, G. F.
Elements of Agriculture 1 10
Warren, G. F.
Farm Management 1 75
Wheeler, H. J.
Manures and Fertilizers 1 60
Widtsoe, John A.
Principles of Irrigation Practice 1 75
THE MACMILLAN COMPANY
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The Rural Outlook Set
By L. H. BAILEY
_Four Volumes. Each, cloth, 12mo. Uniform binding, attractively boxed.
$5.00 per set; carriage extra. Each volume also sold separately._
In this set are included three of Professor Bailey's most popular
books as well as a hitherto unpublished one,--"The Country-Life
Movement." The long and persistent demand for a uniform edition of
these little classics is answered with the publication of this
attractive series.
THE COUNTRY LIFE MOVEMENT
_Cloth, 12mo, 220 pages, $1.25 postage extra_
This hitherto unpublished volume deals with the present movement for
the redirection of rural civilization, discussing the real
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the back-to-the-land movement.
THE OUTLOOK TO NATURE (New and Revised Edition)
_Cloth, 12mo, 195 pages, $1.25 postage extra_
In this alive and bracing book, full of suggestions and encouragement,
Professor Bailey argues the importance of contact with nature, a
sympathetic attitude toward which "means greater efficiency,
hopefulness, and repose."
THE STATE AND THE FARMER (New Edition)
_Cloth, 12mo, $1.25 postage extra_
It is the relation of the farmer to the government that Professor
Bailey here discusses in its varying aspects. He deals specifically
with the change in agricultural methods, in the shifting of the
geographical centers of farming in the United States, and in the
growth of agricultural institutions.
THE NATURE STUDY IDEA (New Edition)
_Cloth, 12mo, $1.25 postage extra_
"It would be well," the critic of _The Tribune Farmer_ once wrote, "if
'The Nature Study Idea' were in the hands of every person who favors
nature study in the public schools, of every one who is opposed to it,
and most important, of every one who teaches it or thinks he does." It
has been Professor Bailey's purpose to interpret the new school
movement to put the young into relation and sympathy with nature,--a
purpose which he has admirably accomplished.
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* * * * *
Transcriber's Notes:
The square root symbol is indicated by sqrt(..)
Exponents are indicated by ^
Bold in a table is indicated by =..=