STORAGE BATTERIES
=Introduction.=—The practical development of the storage battery is
comparatively recent, although a knowledge of the phenomena upon which
its actions are based, dates back to 1801. In 1800, the year made
memorable by Volta's discovery of the galvanic battery, Nicholson and
Carlisle found that a current from Volta's cell could decompose water.
In 1801, Gautherot discovered that if two plates of platinum or
silver, immersed in a suitable electrolyte, be connected to the
terminals of an active primary cell and current be allowed to
flow, a small current could be obtained on an outside circuit
connecting these two electrodes as soon as the primary battery
had been disconnected.
Erman found that the positive pole of such a cell, was the pole
which had been connected to the positive pole of the battery.
In 1803, Ritter observed, with gold wire, the same phenomenon
as Gautherot, and constructed the first secondary battery, by
superposing plates of gold, separated by cloth discs, moistened
with ammonia.
Volta, Davy, Marianini, and others added somewhat to the
knowledge on the subject, and in 1837, Schoenbein found that
peroxide of lead could be used in secondary batteries.
Sir William Grove next came forward with the discovery that
metal plates, with a layer of oxide on them, acted better
than the plain metallic plates, and Wheatstone and Siemens
found still later that peroxide of lead was the best for such
purposes.
In 1842, Grove constructed a gas battery, in which the
electromotive force came from the oxygen and hydrogen evolved
in the electrolysis of water acidulated with sulphuric acid. By
means of fifty such cells, he obtained an arc light.
Michael Faraday, when electrolyzing a solution of lead
acetate, found that peroxide was produced at the positive, and
metallic lead at the negative pole, and in his "Experimental
Researches," he comments on the high conductivity of lead
peroxide, and its power of readily giving up its oxygen.
Although he made no apparent use of this discovery, it may be
considered as the next important step in the development of the
storage battery.
According to Niblett, Wheatstone, de la Rue, and Niaudet were
well aware that peroxide of lead was a powerful depolarizer,
but nobody appears to have made use of this fact until 1860,
when M. Gaston Plante constructed his well known cell with
coiled plates. Plante's researches extended up to 1879, and
practically determined the state of the art.
[Illustration: FIG. 1,046.—One plate or "grid" of a type of storage
cell constructed by inserting buttons or ribbons of the proper chemical
substances in perforations. Some such cells use crimped ribbons of
metallic lead for inserting in the perforations, others pure red lead
or other suitable material.]
As to the theory at this time, it may be stated that Clerk
Maxwell, although the leading electrician of his time, speaks
of the storage battery as storing up a quantity of energy in a
manner somewhat analogous to the ordinary condenser; hence the
use of the word "accumulator" for storage battery.
In 1879, R. L. Metzer did away with the tedious forming
process, by mechanically applying the active material. This
important discovery was not, however, generally known, until
1881, when Camille Faure obtained important patents concerning
the method of shortening the time of formation.
Charles F. Brush, working independently of either Faure or
Metzer, arrived at the same result, and the United States
courts have decided, after long litigation, that to him belongs
the priority of invention in this country.
[Illustration: FIGS. 1,047 to 1,050.—Electric Storage Battery Co.
plates. Fig. 1,047, "Manchester" positive plate; fig. 1,048, box
negative plate; fig. 1,049, "Tudor" positive plate; fig 1,050, pasted
negative plate.]
=Ques. To what use is the storage battery sometimes put in electric
lighting or power stations?=
Ans. To carry the "peak" of the load; that excessive portion of the
load which, for instance, in electric lighting stations has to be
carried only for two or three hours a day. To carry the entire load at
minimum hours. To act as equalizer or reservoir. Also for equipment of
annex or substations.
[Illustration: FIG. 1,051.—"Unformed" plate of one pattern of Gould
storage cell. The particular plate shown has total outside dimensions
of 6×6 inches. The clear outline of the grooves indicates absence of
oxides, due to action of "forming" solutions, or charging current.]
=Theory of the Storage Battery.=—The action of the storage battery
is practically the same as that of the primary battery and it is
subject to the same general laws. The cells of a storage battery are
connected in the same way as primary cells, and when charged is capable
of generating a current of electricity in a manner similar to that
of a primary battery. It differs, however, from the primary battery
in that it is capable of being recharged after exhaustion by passing
an electric current through it in a direction opposite to that of
the current on discharge. This difference constitutes the principal
advantage of the storage battery over the primary battery.
[Illustration: FIGS. 1,052 and 1,053.—Electric Storage Battery Co.,
type H "exide" plates. This form of plate is used for large "stand by"
batteries. Fig. 1,052, positive plate; fig. 1,053, negative plate.]
=Ques. Describe a storage cell.=
Ans. A storage cell consists of plates or of grids in an electrolyte,
of such a character that the electrical energy supplied to it is
converted into chemical energy (a process called charging). The
chemical energy can be reconverted into electrical energy (a process
called discharging).
=Ques. Describe the electrolyte generally used.=
Ans. It consists of a weak solution of sulphuric acid which permits
ready conduction of the current from the primary battery, the greater
the proportion of acid within certain limits, the smaller the
resistance offered.
[Illustration: FIG. 1,054.—Elements of 6 volt 40 ampere hour "Aplco"
portable (3 cell) storage battery. The grids are made from an alloy of
lead and antimony; hard lead straps which are burned together, are used
for joining the plates. Specially treated separators are used.]
=Ques. What is the effect of the current passing through the
electrolyte?=
Ans. It decomposes the water into oxygen and hydrogen; this is
indicated by the formation of bubbles upon the exposed surfaces of
both plates, these bubbles being formed by oxygen gas on the plate
connected to the positive pole of the primary battery, and hydrogen on
the plate connected to the negative pole.
Because, however, the oxygen is unable to attack either
platinum or silver under such conditions, the capacity of such
a device to act as an electrical accumulator is practically
limited to the point at which both plates are covered with
bubbles. After this point the gases will begin to escape into
the atmosphere.
=Ques. What is the prime condition for operation of a storage battery?=
Ans. The resistance of the electrolyte should be as low as possible in
order that the current may pass freely and with full effect between
the electrodes. If the resistance of the electrolyte be too small, the
intensity of the current will cause the water to boil rather than to
occasion the electrolytic effects noted above.
=Ques. What happens when the charging current is discontinued, and the
two electrodes joined by an outside wire?=
Ans. A small current will flow through the outside circuit, being due
to the recomposition of the acid and water solution. The process is
in a very definite sense a reversal of that by which the current is
generated in a primary cell.
Hydrogen collected upon the negative plate, which was the
cathode, so long as the primary battery was in circuit, is
given off to the liquid immediately surrounding it, uniting
with its particles of oxygen and causing the hydrogen, in
combination with them, to unite with the particles of oxygen
next adjacent. The process is continued until the opposite
positive plate is reached, when the oxygen collected there is
finally combined with the surplus hydrogen, going to it from
the surrounding solution.
This chemical process causes the current to emerge from the
positive plate, which was the anode, so long as the primary
battery was in circuit. The current thus produced will continue
until the recomposition of the gases is complete; then ceasing
because these gases, as before stated, do not combine with the
metal of the electrodes.
=Types of Storage Battery.=—There are three classes of storage cell
which are commercially important:
1. Plante cells;
2. Faure cells;
3. Alkaline cells.
According to construction secondary cells may be classified as follows:
1. Lead sulphuric acid cells;
2. Lead copper cells;
3. Lead zinc cells;
4. Alkaline zincate cells.
The lead sulphuric acid type includes all those cells belonging
to the Plante and Faure groups.
Lead copper cells consist of sheets of metal coated with lead
oxide, serving as the positive electrode, and copper plates
for the negative electrodes. These plates are immersed in a
solution of copper sulphate. Cells belonging to this class are
not employed in commercial practice, being useful only for
laboratory experiments.
Lead zinc cells are similar to the preceding type, but differ
by having zinc for the negative electrode, and zinc sulphate
for the electrolyte. The voltage of these cells is slightly
higher than that of the ordinary cell, and their capacity per
unit of total weight is high, but they are apt to lose their
charge on open circuit, besides they possess most of the
disadvantages of the Plante cells.
Alkaline zincate cells have copper for the positive, and iron
for the negative electrode. The electrolyte is composed of
sodium, or potassium, zincate. Cells of this type are used to
some extent for traction purposes.
In addition to the above there are some special forms of cell
which do not belong to the four preceding types.
=Ques. Describe the Plante type.=
Ans. In the Plante type the lead is chemically attacked and finally
converted into lead peroxide, probably after it has gone through
several intermediate changes. The plates are all formed as positive
plates first and then all that are intended for negative plates are
reversed, the peroxide being changed into sponge lead.
[Illustration: FIGS. 1,055 and 1,056.—Willard plates; fig. 1,055,
negative plates; fig. 1,056, positive plates. Both positive and
negative plates are of the Planté type, made from one integral piece
of rolled lead. These are grooved plates. The projections are tapered,
that is, they are wider at the base than at the surface, for strength.
The center web of each positive plate is tapered from the top of the
plate downward to secure uniform distribution of the current all over
the surface of the plate.]
[Illustration: FIG. 1,057.—Wood separator for spacing the plates, as
used in the Willard storage cells.]
[Illustration: FIG. 1,058.—Positive plate.]
[Illustration: FIG. 1,059.—Perforated rubber separator.]
[Illustration: FIG. 1,060.—Wood separator.]
[Illustration: FIG. 1,061.—Negative plate.]
[Illustration: FIG. 1,062.—Hard rubber cover.]
[Illustration: FIG. 1,063.—Vent plug.]
[Illustration: FIG. 1,064.—Pillar connecting strap.]
[Illustration: FIG. 1,065.—Hard rubber jar.]
[Illustration: FIG. 1,066.—Complete element.]
[Illustration: =Figs. 1,058 to 1,066.—Parts of the Willard "Autex"
automobile cells.=]
=Ques. What is done to make the Plante plate more efficient?=
Ans. The surfaces are finely subdivided, the following methods being
those common: scoring, grooving, casting, laminating, pressing, and by
the use of lead wool.
=Ques. Describe the Faure or pasted type.=
Ans. This form of plate is constructed by attaching the active material
by some mechanical means to a grid proper. The active material first
used for this purpose was red lead, which was reduced in a short time
to lead peroxide when connected as the positive or anode, or to spongy
metallic lead when connected as the cathode or negative, thus forming
plates of the same chemical compound as in the Plante type.
The materials used at the present time by the manufacturers
for making this paste are largely a secret with them, but in
general they consist of pulverized lead or lead oxide mixed
with some liquid to make a paste.
=Ques. How do Faure plates compare with those of the Plante type?=
Ans. They are usually lighter and have a higher capacity, but have a
tendency to shed the material from the grid, thus making the battery
useless.
Many ways have been tried for mechanically holding the active
material on the grid, the general method involving a special
design in the shape of the grid. Some of these designs are:
1, solid perforated sheets of lattice work; 2, corrugated and
solid recess plates not perforated; 3, ribbed plates with
projecting portions; 4, grid cast around active material; 5,
lead envelopes, and 6, triangular troughs as horizontal ribs.
=The Electrolyte.=—Sulphuric acid is generally used as electrolyte;
the acid should be made from sulphur and not from pyrites, as the
latter is liable to contain injurious substances.
=Ques. How is the electrolyte prepared?=
Ans. One part of chemically pure concentrated sulphuric acid is mixed
with several parts of water. The proportion of water differs with
several types of cell from three to eight parts, as specified in the
directions accompanying the cells.
[Illustration: FIGS. 1,067 to 1,079.—Willard connecting straps and
connectors.]
=Ques. What test is necessary in preparing the electrolyte?=
Ans. In mixing the water and acid, the hydrometer should be used to
test the specific gravity[6] of both the acid and the solution. The
most suitable acid should show a specific gravity of about 1.760 or 66°
Baumé.
[6] NOTE.—_Specific gravity_ is the weight of a given substance
relative to an equal _bulk_ of some other substance which is taken as
a standard of comparison. Water is the standard for liquids. In the
laboratory the _specific gravity bottle_ is often used in determining
the specific gravity of a liquid. The capacity of the bottle is 1,000
grains of pure water. When it is filled with spirits of wine and
weighed in a balance (together with a counterpoise for the weight of
the bottle, which of course is constant), it will weigh considerably
less than 1,000 grains; in fact, the bottle will contain only about 917
grains of proof spirit; therefore, taking the specific gravity of water
as unity, 1 or 1.000, the specific gravity of spirits of wine is 0.917.
If, on the other hand, the bottle be filled with sulphuric acid, it
will weigh about 1,850 grains; hence, the specific gravity of sulphuric
acid is said to be 1.850. A more convenient method for the automobilist
is by the use of the hydrometer.
=Ques. In preparing the electrolyte, how should the water and acid be
mixed?=
Ans. The mixture should be made by pouring the acid slowly into the
water, _never the reverse_. As cannot be too strongly stated, in
mixing, the liquid should be stirred with a clean wooden stick, the
acid being added to the water slowly; the latter is corrosive and will
painfully burn the flesh.
Distilled or rain water should be used in preparing the
electrolyte. When made, the solution should be allowed to cool
for several hours or until its temperature is approximately
that of the atmosphere (60 being the average). At this point it
should have a specific gravity of about 1.200 or 25° Baumé. If
the hydrometer show a higher reading, water may be added until
the correct reading is obtained; if a lower reading, dilute
acid may be added with similar intent.
The electrolyte should never be mixed in jars containing the
battery plates, but preferably in stone vessels, specially
prepared for the purpose. Furthermore, it should never be
placed in the cell until perfectly cool.
=Ques. What is the effect of mixing the acid and the water?=
Ans. The mixture becomes hot.
Before using, the mixture should be allowed to cool.
=Ques. What kind of a vessel should be used?=
Ans. The vessel should be of glass, glazed earthenware, or lead.
=Ques. At what density is the resistance of dilute sulfuric acid at a
minimum?=
Ans. At 1.260.
The percentage of concentrated sulphuric acid and of water per
100 parts of the electrolyte for various specific gravities is
given by the following table:
SPECIFIC GRAVITY TABLE
+——————————————+————————————+————————————————+
|Sulphuric acid| Water |Specific gravity|
| (Per cent.). |(Per cent.).| of Mixture. |
+——————————————+————————————+————————————————+
| 50 | 50 | 1.398 |
| 47 | 53 | 1.370 |
| 44 | 56 | 1.342 |
| 41 | 59 | 1.315 |
| 38 | 62 | 1.289 |
| 35 | 65 | 1.264 |
| 32 | 68 | 1.239 |
| 29 | 71 | 1.215 |
| 26 | 74 | 1.190 |
| 23 | 77 | 1.167 |
| 20 | 80 | 1.144 |
| 17 | 83 | 1.121 |
| 14 | 86 | 1.098 |
| 10 | 90 | 1.068 |
+——————————————+————————————+————————————————+
The electrolyte of the desired specific gravity may be
purchased ready for use, but in cases where it is desirable
to save freight, the acid may be diluted at the point of
installation.
=Ques. What is the effect of a deep containing vessel?=
Ans. Parts of the plate surface may do more than their share of the
work due to the difference in the density of the electrolyte at the top
and bottom. The containing vessel should, therefore, never be deeper
than about 20 inches unless some artificial means of acid circulation
be used.
=Ques. What is the effect of changes in temperature on the electrolyte?=
Ans. The resistance of the electrolyte is changed, being less for
increase of temperature.
[Illustration: FIGS. 1,080 to 1,084—Acid hydrometers for liquids
heavier than water. Fig. 1,080, standard storage battery hydrometer
with guiding points designed for "hydrometer syringe," shot bulb, with
red line at 25 Baumé, 5 inches long, double scale 10 to 40 Baumé, 1.050
to 1.400 specific gravity. Fig. 1,081, plain hydrometer with shot bulb,
5 inches long, double scale 10 to 40 Baumé, 1.050 to 1.400 specific
gravity. Figs. 1,082 and 1,083, hydrometer with small flat bulb, used
in car lighting batteries, shot bulb, 4½ inches long, single scale,
reading from 1.100 to 1.250 specific gravity. Fig. 1,084 jar for
hydrometers.]
=Ques. How should the cells be filled?=
Ans. Enough of the electrolyte should be poured into the jars to
completely cover the plates, or to within about a half inch of the top
edge of the jar. Large cells should be filled by means of an acid proof
pump and rubber hose.
=Ques. What change takes place after filling the jars?=
Ans. The specific gravity of the electrolyte will fall considerably,
but will rise again when the battery is charged.
=Ques. What may be said with respect to the density of the electrolyte?=
Ans. It should never exceed 1.200 when the battery is fully charged.
=Ques. How much electrolyte is used per 100 ampere hours battery
capacity, on an 8 hour rating?=
Ans. About ten pounds; in automobile batteries, about four pounds is
sufficient.
[Illustration: FIG. 1,085.—The hydrometer syringe; a convenient device
for testing electric vehicle cells. By slightly compressing the bulb
and inserting the slender tube through the vent hole in the cover of
the cell sufficient acid may be drawn up to float the hydrometer within
the large glass tube, and the reading can be made at once. The acid is
returned to the cell by again compressing the bulb, and the reading of
the next cell taken. The laborious and uncleanly method of drawing out
sufficient acid by a syringe is thus avoided.]
=Ques. What may be said with respect to impurities in the electrolyte?=
Ans. The electrolyte should be free from chlorine, nitrates, acetates,
iron, copper, arsenic, mercury, and the slightest trace of platinum.
Mercury alone has no injurious effect unless it be present
in sufficient quantity to amalgamate the plates, but in
combination with any other metal, may cause local action.
[Illustration: FIGS. 1,086 to 1,089.—The "Champion" Accumulator;
views showing parts and assembly. Fig. 1,086, empty plate; fig. 1,087,
filled plate; fig. 1,088, complete element, small type; fig 1,089, cell
assembled. The plates are of the envelope type and are made thick. The
active material is held firmly in place by a covering of lead. A few
thick plates are used instead of many thin ones.]
The following tests should be made for impurities before the
electrolyte is poured in the cells:
=Chlorine.=—To a small sample of the electrolyte add a few
drops of silver solution (20 grains of silver dissolved in
1,000 cu. cm. of water). A white precipitate indicates chlorine.
=Nitrates.=—Place some of the electrolyte in a test tube,
and add 10 grains of strong ferrous sulphate solution.
Carefully pour down the side of the test tube a small amount of
chemically pure concentrated sulphuric acid. A brown stratum
between the electrolyte and the concentrated acid indicates the
presence of nitric acid.
=Acetic acid.=—Neutralize the electrolyte with ammonia,
then add ferric chloride. If the solution turns red, and is
afterwards bleached by the addition of hydrochloric acid,
acetic acid is present.
=Iron.=—Neutralize a sample of the electrolyte with ammonia;
boil a small portion with hydrogen peroxide, and add ammonia or
caustic potash solution until the mixture becomes alkaline. If
a brownish red precipitate forms, it indicates iron.
=Copper.=—If copper be present, a bluish white precipitate
will be formed when ammonia solution is added to the
electrolyte.
[Illustration: FIG. 1,090.—One cell of the Gould storage battery for
electric vehicle use. According to the data given by the manufacturers,
this cell, containing four negative and three positive plates, has a
normal charging rate of 27 amperes; a distance rate of 22 amperes for
four hours; a capacity of 81 ampere hours at 3 hours discharge, and of
90 ampere hours at 4 hours discharge. Forty such cells are generally
used for an average light vehicle battery.]
=Mercury.=—This is indicated by an olive green precipitate
when a solution of potassium iodide is added to the
electrolyte, or by a black precipitate when lime water is added.
=Platinum.=—A rough test for traces of platinum is made by
pouring the electrolyte into a cell in which the battery plates
are immersed. If gassing take place for some time on open
circuit, it is an indication of the presence of platinum.
=Ques. What should be done with old electrolyte?=
Ans. When a battery is taken down the electrolyte may be saved and used
when re-assembling the battery, providing great care be exercised when
pouring it out of the jar, so as not to draw off with it any of the
sediment. It should be stored in convenient receptacles, preferably
carboys, which have been thoroughly washed and never used for any other
purpose.
[Illustration: FIG. 1,091.—Phantom view of an "Exide" sparking or
ignition battery. It contains three cells. In this type, the terminal
lug has been designed to obviate the creeping of the electrolyte with
its accompanying corrosion. The positive and negative terminals are for
identification.]
The electrolyte saved in this manner will not, however, be
sufficient to refill the battery, and as some new electrolyte
will be required, in general it is recommended that the old
supply be thrown away and all new electrolyte (1.200 specific
gravity) be used when re-assembling.
=Voltage of a Secondary Cell.=—This depends on the density of the
electrolyte, the character of the electrodes and condition of the cell;
it is independent of the size of the cell.
The voltage of a lead sulphuric acid cell when being charged is from 2
to 2.5 volts. While the cell is being discharged, it decreases from 2
to 1.7 volts. The voltage due to the density of the electrolyte may be
calculated from the following formula:
V = 1.85 + .917 (S - s)
in which
V = voltage;
S = specific gravity of the electrotype;
s = specific gravity of water at the temperature of observation.
[Illustration: FIG. 1,092.—The Exide storage cell. The positive and
negative plates are separated by thin sheets of perforated hard rubber,
placed on both sides of each positive plate. The electrolyte and plates
are contained in a hard rubber jar.]
[Illustration: FIG. 1,093.—An Exide battery of five cells. The box
which holds the cells is usually made of oak, properly reinforced,
with the wood treated to render it acid proof. The terminals as shown,
consist of metal castings attached to the side of the box and plainly
marked.]
=Connection for Charging.=—The dynamo cable connections may be made
either before or after filling the cells. In making these connections
great care should be taken to be sure that the positive terminal of the
battery is connected to the positive lead of the dynamo, and that the
negative terminal of the battery is connected to the negative lead of
the dynamo. In order to insure that the reverse connections are not
made accidentally, the dynamo leads should be tested by a pole tester,
and the positive and negative poles marked red and black respectively.
[Illustration: FIGS. 1,094 to 1,109.—Parts of the "Exide" sparking
battery. A, positive plate; B, negative plate; C, wood separator; D,
positive strap; E, negative strap; F, terminal lug; H, connector; I,
terminal bolt connector, stud, thumb nut and hexagonal nut; J, copper
washer for bolt connector; L, hard rubber jar; M, hard rubber cover;
N, hard rubber cylinder vent; O, vent plug for cylinder vent; R,
wood case; S, strap handle; T, fitting for strap handle. The "Exide"
sparking battery is also adapted for electric lighting of automobiles,
for head lights, tail lights, side and interior lights.]
The polarity of the dynamo wires being determined, they may be joined
to the proper terminals by means of suitable clamps or by solder.
Wherever possible the dynamo should be of the direct current, shunt
wound, or special compound type, but in cases where only alternating
current can be obtained, suitable rectifiers or converters should be
used for changing it to direct current.
=Charging.=—Before beginning to charge a storage battery, it should
be gone over carefully, and any cell that is not up to the standard
should be disconnected and put in working order before being replaced.
In general, if the current used in charging be too large, it will
waste energy by evolving an excess of heat and gas; if too small,
an insulating deposit of white lead sulphate will be formed on the
positive plate, thereby preventing the formation of the proper amount
of lead peroxide.
[Illustration: FIGS. 1,110 and 1,111.—Switchboard and motor dynamo
circuit connections for charging a battery from direct current mains.]
=Ques. How should a battery be charged for the first time?=
Ans. It is essential that the current be allowed to enter at the
positive pole at about one-half the usual charging rate prescribed, but
after making sure that all necessary conditions have been fulfilled, it
is possible to raise the rate to that prescribed by the manufacturers
of the battery.
=Ques. What is the usual period for charging a new battery?=
Ans. With several of the best known makes of storage battery the
prescribed period for the first charge varies between twenty and thirty
hours.
[Illustration: FIGS. 1,112 and 1,113.—Switchboard and motor generator
circuit connections for charging a battery from alternating current
mains. The connections of a third wire are shown, for use in case a
three phase circuit is available.]
=Ques. How is the electrolyte affected by the first charge?=
Ans. A change of specific gravity occurs. The specific gravity should
be about 1.200 when the solution is poured into the cells.
At the completion of the first charge, it should, on the same
scale be about 1.225. If it be higher than this, water should
be added to the solution until the proper figure is reached, if
it be lower, dilute sulphuric acid should be added until the
hydrometer registers 1.225.
At the first charging of a cell, when the pressure has reached
the required limit, the cell should be discharged until the
voltage has fallen to about two-thirds normal pressure, when
the cell should again be recharged to the normal voltage (2.5
or 2.6 volts).
The manufacturers of a well known cell of the Plante genus
prescribe for the first charge, half rate for four hours, after
which the current may be increased to the normal power and
continued for twenty hours successively.
[Illustration: FIG. 1,114.—Plates of Edison storage battery. The
positive or nickel plate consists of one or more perforated steel
tubes, heavily nickel plated, filled with alternate layers of nickel
hydroxide and pure metallic nickel in excessively thin flakes. The
tube is drawn from a perforated ribbon of steel, nickel plated, and
reinforced with eight steel bands, equidistant apart, which prevent the
tube expanding away from and breaking contact with its contents. The
tubes are flanged at both ends and held in perfect contact with a steel
supporting frame or grid made of cold rolled steel, nickel plated. The
negative or iron plate consists of a grid of cold rolled steel, nickel
plated, holding a number of rectangular pockets filled with powdered
iron oxide. These pockets are made up of very finely perforated steel,
nickel plated. After the pockets are filled they are inserted in the
grid and subjected to great pressure between dies which corrugate the
surface of pockets and force them into good contact with the grid.]
=Ques. What strength of current should be used in charging a cell?=
Ans. It should be in proportion to the ampere hour capacity of the
cell.
Thus, as given by several manufacturers, the normal charging
rate for a cell of 40 ampere hours should be five amperes, or
one-eighth of its ampere hour rating in amperes of charging
current.
=Ques. What should be the voltage of the charging current before
closing the charging circuit?=
Ans. The voltage should be at least ten per cent. higher than the
normal voltage of the battery when charged.
[Illustration: FIG. 1,115.—Complete element of Edison storage battery
with insulators. After the plates are assembled into a complete
element, narrow strips of treated hard rubber are inserted between the
plates, thereby separating and insulating them from each other. The
side insulator is provided with grooves that take the edges of the
plates, thereby performing the dual function of separating the plates
and insulating the complete elements from the steel container. At the
ends of the element, that is between the outside negative plates and
container, are inserted smooth sheets of hard rubber. At the bottom,
the element rests upon a hard rubber rack or bridge, insulating the
plates from the bottom of container.]
[Illustration: FIG. 1,116.—Four Edison cells (type A-4) in wooden
tray.]
=Ques. What indicates the completion of a charge?=
Ans. When a cell is fully charged the electrolyte apparently boils and
gives off gas freely. The completion of a charge may be determined by
the voltmeter, which will show whether the normal pressure has been
attained.
=Ques. How should the voltage be regulated during the first charge?=
Ans. It should be allowed to rise somewhat above the point of normal
pressure.
Electrical Data Edison Cell
+——————————————————————————————————————————————————————————————+
| =B-2= =B-4= =B-6=|
|Normal output, ampere hours 40 80 120 |
| |
|Maximum output, ampere hours 48 95 142 |
|Normal rate of discharge, amperes for |
| five hours 8 16 24 |
| |
|Average voltage on normal discharge 1.2 1.2 1.2 |
| |
|Normal rate of charge, amperes for |
| seven hours 8 16 24 |
| |
|Maximum rate of "boosting charge" |
| (for short time only) 50 100 140 |
| |
|Length of containing can (determined |
| by number of plates) 1½ 2⅝ 3-13/16 |
| |
|Width of containing can 5⅛ 5⅛ 5⅛ |
| |
|Height " " " 7-15/16 7-13/16 7¾ |
| |
|Height over all 8¾ 8¾ 8⅞ |
| |
|Weight of each cell alone, lbs. 4.6 7.4 10.5 |
| |
|Average weight per cell of battery, |
| assembled in trays 5.5 8.7 11.8 |
+——————————————————————————————————————————————————————————————+
[Illustration: FIG. 1,117.—Cell of Edison storage battery. The jar or
container is of nickel plated sheet steel with welded seams; the walls
are corrugated to give strength. The cell cover, of sheet steel, has
four mountings, two being pockets to contain stuffing boxes about the
terminal posts. One of the other two is a separator which separates
spray from the escaping gas while the battery is charging. The fourth
mounting is for filling with electrolyte. The electrolyte consists of
a 21% solution of potash in distilled water with a small per cent. of
lithia. The density of the electrolyte does not change on charge or
discharge.]
=Ques. How often should a battery be charged?=
Ans. At least once in two weeks, even if the use be only slight in
proportion to the output capacity.
In charging a storage battery, it is essential to remember the
fact that the normal charging rate is in proportion to the
voltage of the battery.
Thus, a 100 ampere hour battery, charged from a 110 volt
circuit at the rate of ten amperes per hour, would require ten
hours to charge, and would consume in that time an amount of
electrical energy represented by the product of 110 (voltage)
by 10 (amperes) which would give 1,100 watts, or 1⅒ kw.
[Illustration: FIG. 1,118.—Diagram illustrating method of charging
storage battery of stationary gas engine ignition system; the system
is simple to install and will give satisfactory results. Two storage
batteries are used, one being charged while the other is operating
the sparking coil. Where charging current is available at the point
where the batteries are used, the following diagram shows the system
of connections, which can be easily followed, A represents the source
of charging current and B the bank of lamps (or other resistance, such
as an ordinary rheostat) sufficient to cut down the charging voltage
to that required by the battery. C and D are two double pole double
throw knife switches connected at their hinges to two batteries, E and
F, each consisting of a group of cells. G represents the leads to the
sparking coil terminals. From the diagram, it will readily be seen
that by throwing the switches in opposite directions one battery will
be charging while the other battery is discharging to the engine, thus
giving a constant source of supply, and insuring that the spare battery
will be full and ready for service by the time the other is discharged.
The method of determining the necessary resistance for cutting down the
line voltage for charging the battery is illustrated by the following
example: If a battery require about 3 amperes for charging, how is this
current obtained from a 110 volt circuit? Each 16 candle power carbon
filament lamp in the lamp bank would give approximately ⅓ ampere with
the cells in series in the lamp circuit. Therefore, 3 x 3 or 9 lamps
should be used in parallel to give 3 amperes.]
=Ques. If in charging a battery, one or more of the cells do not boil
at the completion of the charge, or fail to show the proper voltage,
what should be done?=
Ans. The charging must be continued until the cadmium test shows the
required voltage, but if the prolonging of the charge be liable to
damage the plates in the other cells, the defective cell or cells
should be cut out of circuit when the battery discharges and then
placed in circuit again when the battery is recharged. If the desired
result cannot be attained by this method, the plates which require
additional charging may be charged in a separate cell.
[Illustration: FIGS. 1,119 and 1,120.—Emergency connections for weak
ignition battery. It sometimes occurs through carelessness or neglect,
that the storage battery is discharged so low that the engine explosion
will not take place, and it is necessary to run somehow or other for a
short time. In such cases the following suggestion may be followed: If
there be two storage batteries, connect them in series. If there be one
storage battery and a set of dry cells, connect the positive terminal
of the storage battery to the negative or outside terminal of the dry
cell; set and connect to the coil leads as if they were one battery.
The above suggestions should only be followed in emergency, for it may
injure the coils, and is harmful to the battery.]
=Ques. How is the cadmium test made?=
Ans. A plate of cadmium is mounted in a hard rubber frame and immersed
in the electrolyte. The test consists in taking voltage readings
between the cadmium plate and the positive or negative plates of the
cell. During charge the cadmium plate reads negative to the negative
plate, until the cell is about full, when the reading should be
zero; the charge should be continued until the cadmium reads 0.2 volt
positive to the negative while charging at the normal rate.
=Ques. Name some portable instruments that should be provided for
testing batteries.=
Ans. 1, a hydrometer syringe (specific gravity tester); 2, an acid
testing set (can be used instead of the syringe); 3, a low reading
voltmeter; 4, suitable prods, and 5, a thermometer.
=Ques. What precaution should be taken in charging a battery?=
Ans. Care should be taken not to have a naked flame anywhere in its
vicinity.
To either charge or discharge a battery at too rapid a rate
involves the generation of heat. Thus, while this is not liable
to result in a flame under usual conditions, the battery may
take fire, if it be improperly connected or improperly used.
=Ques. What is the effect of varying the charging current?=
Ans. In charging a storage cell, particularly for the first time, a
weaker current than that specified may be used with the same result,
provided the prescribed duration of the charge be proportionally
lengthened. The battery may also be occasionally charged beyond the
prescribed voltage, ten or twenty per cent. overcharge effecting no
injury, although if frequently repeated, it shortens the life of the
battery.
=Ques. What are the charge indications?=
Ans. The state of the charge is not only indicated by the density of
the electrolyte and the voltage of the cell, but also by the _color of
the plates_, which is considered by many authorities as one of the best
tests for ascertaining the condition of a battery.
[Illustration: FIGS. 1,121 and 1,122.—Two methods of charging from a
direct current lighting system. The simplest method of charging is from
an incandescent light circuit, using lamps connected in parallel to
reduce the voltage to that of the battery, the current being adjusted
by varying the number of lamps in circuit. The group of lamps is in
series with the battery to be charged, and the combination is connected
across the circuit furnishing the current. If the charging source be a
110-120 volt circuit, and the rate required be 6 amperes, twelve 16 c.
p. or six 32 c. p. lamps, in parallel, and the group in series with the
battery, will give the desired charging rate, unless high efficiency
lamps be used, when more will be required. In case a lower charging
rate, say 2 amperes be used, then a proportionately fewer number of
lamps will be needed; but the length of time required to complete
the charge will be correspondingly increased. Instead of lamps, as
in fig. 1,121, a rheostat is sometimes used, as shown in fig 1,122.
Its resistance should be such as to produce, when carrying the normal
charging current, a drop in volts equal to the difference between the
pressure of the charging source and that of the battery to be charged;
thus, if a battery of three cells, giving 6 volts, is to be charged
from a 110 volt circuit at a 6 ampere rate, the resistance would be,
according to Ohm's law,
(110 - 6) ÷ 6 = 17.3 ohms.
The carrying capacity of the rheostat should be slightly in excess
of the current required for charging. An ammeter with suitable scale
should be inserted in the battery circuit to indicate the current.
For charging more than one battery at a time from a 110 volt circuit,
the batteries should be connected in series (positive terminal of one
battery to the negative of the next, and so on). The charging rate
should be that of the battery with the lowest rate. The resistance to
be inserted will be less than if only one battery is being charged;
where lamp resistance is used, _this means more lamps in parallel_.
Care should be taken to remove each battery from the circuit as it
becomes charged, inserting additional resistance to take its place.]
=Ques. What are the colors of the plates?=
Ans. In the case of formed plates, and before the first charging, the
positives are of a dark brown color with whitish or reddish gray spots,
and the negatives are of a yellowish gray. The whitish or reddish gray
spots on the positive plates are small particles of lead sulphate which
have not been reduced to lead peroxide during the process of forming,
and represent _imperfect sulphation_.
As a general rule, the first charging should be carried on
until these spots completely disappear. After this the positive
plates should be of a dark red or chocolate color at the end of
the discharge, and of a wet slate or nearly black color when
fully charged. A very small discharge is sufficient, however,
to change them from black to the dark red or chocolate color.
If the battery has been discharged to a pressure lower than 1.8
volts, the white sulphate deposits will reappear, turning the
dark red color to a grayish tint in patches or all over the
face of the plate, or in the form of scales of a venetian red
color.
_The formation of these scales_ while charging indicates that
the maximum charging current is too large and should be reduced
until the scales or white deposits fall off or disappear, after
which the current can be increased again.
During charging, the yellowish gray color of the negatives
changes to a pale slate color which grows slightly darker at
the completion of the charge. The color of the negatives always
remains, however, much lighter than that of the positives.
=Ques. How are the best results obtained in charging?=
Ans. The rate of charge should be normal, except in cases of emergency.
At such a rate, unless the constant voltage method be employed, the
cell may be considered full when the voltmeter reads 2.5 volts during
charge. The electrolyte should be kept at uniform density throughout
the cell; when water is added, because of evaporation, it should be
added by means of a funnel reaching to the bottom of the cell. Care
should be taken never to add acid after evaporation; otherwise the
electrolyte will be too heavy. Hydrometer readings should be taken
regularly; the reading is an excellent indication of the amount of
charge in the battery. Hydrometer readings are useless, however, unless
the precaution be taken to keep the electrolyte of uniform density.
=Ques. What voltage should be used in charging?=
Ans. At the beginning of the charge the voltage should be about 5 per
cent. higher than the normal voltage of the battery, unless the latter
has been overdischarged, in which case the difference of pressure
should not exceed 2 per cent., otherwise the current might be too large.
[Illustration: FIG. 1,122.—Diagram showing charging connections for
"Exide" duplex sparking battery. C, charging source; D, double pole
single throw switch; E, single pole single throw switch; M, lamp
resistance "main" battery; R, lamp resistance "reserve" battery.]
=Ques. In what two ways may batteries be charged?=
Ans. They may be charged either at constant current or at constant
voltage.
Although the latter method is considered the better one by many
authorities, it is a fact, nevertheless, that if the charging
current be normal at the beginning of the charge, and no means
be provided for keeping it constant, it will diminish as the
charging progresses, thereby greatly increasing the length of
the time required for charging, and resulting in serious injury
to the plates.
=Ques. How may the charging current be kept constant?=
Ans. Its voltage should be gradually increased, first to about 10 or
15 per cent. above the voltage of the battery, and kept at that point
nearly to the end of the charge, where in consequence of the rapid rise
of pressure in the battery it might become necessary to increase the
voltage of the current to 30 or 40 per cent. above the normal of the
battery.
[Illustration: FIGS. 1,124 to 1,126.—Electric Storage Battery Co.
chloride cells. The voltage of cells of all capacities is slightly
above 2 volts on open circuit, and during discharge at the 8 hour rate
it varies from that point at the beginning to 1.75 volts at the end.]
=Ques. What tests should be made while charging?=
Ans. Occasional voltage and cadmium readings of each cell should be
taken for the purpose of ascertaining their condition and the behavior
of the separate plates.
=Ques. What tests should be made after charging?=
Ans. Each cell should be tested with a low reading voltmeter and
hydrometer about once a week. If any cell read low, it should be cut
out and examined to see if any material has been introduced which
would cause a short circuit. If this trouble do not exist, the cell
should be given an independent charge.
=Charge Indications.=—The state of the charge is not only indicated by
the density of the electrolyte and the voltage of the cell, but also by
the _color of the plates_, which is considered by many authorities as
one of the best tests for ascertaining the condition of a battery.
In the case of formed plates, and before the first charging,
the positives are of a dark brown color with whitish or
reddish gray spots and the negatives are of a yellowish gray.
The whitish or reddish gray spots on the positive plates are
small particles of lead sulphate which have not been reduced
to lead peroxide during the process of forming, and represent
_imperfect sulphation_.
As a general rule the first charging should be carried on until
these spots completely disappear. After this, the positive
plates should be of a dark red or chocolate color at the end
of a discharge and of a wet slate or nearly black color when
fully charged. A very small discharge is sufficient, however,
to change them from black to the dark red or chocolate color.
If the battery has been discharged to a pressure lower than 1.8
volts, the white sulphate deposits will reappear turning the
dark red color to a grayish tint in patches or all over the
surface of the plate, or in the form of scales of a venetian
red color.
The _formation of these scales_ during charging indicates that the
maximum charging current is too large and should be reduced until the
scales or white deposits fall off or disappear, after which the current
can be increased again.
=Ques. Describe the behavior of the electrolyte during discharge.=
Ans. There is a definite change in the density of the electrolyte for a
given amount of discharge.
The density of the electrolyte is, therefore, one of the best
indications of the state of charge, provided, of course, no
internal discharge due to local action takes place. If, when
the cell is charged, it show a density of 1.200, and when
discharged 1.130, the difference .07 represents the total
charge. If at any time the density be 1.165, then just one half
the amount of capacity has been taken from the cell.
It is necessary to stir the electrolyte well, in order for
these observations to be reliable.
If the discharge has taken place at a high rate, the cell
must stand for an hour or more before the electrolyte will
completely diffuse so that the density readings are correct.
[Illustration: FIG. 1,127.—Electric Storage Battery Co., arc lead
burning outfit. In assembling a storage battery element, a negative
plate is laid down with a separator on it, then a positive plate,
separator, negative plate, etc. The plates are so placed that all the
lugs of the positive plates are on one side and all the lugs of the
negative plates are on the other side. A strip, consisting of flat
strips of lead or lead alloy, having rectangular openings in it of the
same dimensions as the cross section of the lug of the plates, these
openings being spaced to register with the lugs, is then placed over
the plate lugs of the positive plates and a similar strap is placed
over the lugs of the negative plates. The lugs are then burned into
integral union with the straps.]
=Ques. Define the term "boiling."=
Ans. Boiling means the rapid evolution of gas when a cell is nearly
charged.
=Ques. What causes boiling?=
Ans. The amount of sulphate to be converted into peroxide becomes less
and less as the charge progresses and the plates therefore become
virtually smaller, so that the current becomes too large for the work
demanded of it. The result is, that part of the current not actually
used in the formation of peroxide decomposes the electrolyte into its
constituent elements.
=Ques. Why do the gases evolved produce a less milky appearance of the
electrolyte when a battery has been in use for a considerable time?=
Ans. The plates are better formed; consequently a larger charging
current can be used without producing "boiling".
[Illustration: FIG. 1,128.—Hydrogen gas generator for lead burning.
A complete lead burning outfit consists of the following parts: 1,
hydrogen gas generator; 2, trap for cleaning the gas and for preventing
the flame getting back in the generator; 3, air pump; 4, air tank; 5,
blow pipe; 6, lead burner's mixing tee; 7, length of 150 feet 5/16 inch
soft rubber tubing. When the generator is to be used for lead burning,
connect up the different parts of the apparatus as shown. Fill the trap
⅔ full with water and be sure to connect the gas generator to the
nipple on the bottle marked B. The stop cocks N and C must be closed.
See that the rubber plug at D is secured in place. Put the required
amount of zinc in the opening at H. (No. 1 generator requires: 15 lbs.
zinc, 9 gals, water, 3 gal. vitriol. No. 2 generator requires: 20 lbs.
zinc, 15 gals. water, 5 gals. vitriol). After putting in the zinc, add
the water and then the sulphuric acid, _and note that the water must
always be put in before the acid_. When making the connection be sure
that there are no low points in the hose between E and N, as water
is liable to accumulate at these low places, which will make the gas
damp which is detrimental to the burning. If water get into the line,
kink the hose between F and B, detach the hose at E and blow out the
water with air by opening the cocks, N, C and V. The length of the hose
between T and X must not be longer than five feet as the cocks N and C
must always be within the reach of the man who is using the flame. When
ready to use the flame, open N which allows the hydrogen gas to escape.
Light the same with a match and adjust the air cock C until the desired
flame is obtained. Different classes of work require different flames,
which can be obtained by changing the tips and by varying the amount of
gas and air with the cocks N and C. When the generator is laid up for
the night, or when the charge is exhausted, pull the hose off at F and
draw off the solution by removing the plug at D. The generator should
then be thoroughly washed by pouring water in A.]
=Ques. What may be said of charging a battery as quickly as possible?=
Ans. As a general rule, such a procedure should not be adopted unless
the battery be thoroughly discharged.
=Ques. What precaution should be taken?=
Ans. The danger to be avoided in rapidly charging a cell is its
tendency to heat.
=Ques. What apparatus is necessary in charging a battery?=
Ans. The battery may be charged from direct current mains having the
proper voltage. A current as near uniform as possible is required,
and existing conditions must be met in each separate case. Sometimes
a motor dynamo set with a regulating switchboard is used. Such an
apparatus consists of a direct current dynamo, driven direct from the
shaft of a motor, which, in turn, is energized by current from the line
circuit.
With a direct current on the line, a direct current dynamo may
be used; but with an alternating current an induction motor is
required. The speed of the motor is governed by a rheostat, and
the output of the dynamo is thus regulated as desired.
=Charging Through the Night.=—If an electric vehicle, after a late
evening run, is to be used in the morning, the battery may be charged
during the night without an attendant being present; but in doing this
great care must be taken not to excessively overcharge.
A careful estimate of the amount of current required should be made and
the rate of charge based on this estimate.
If, say, 72 ampere hours be required to recharge, and the time
available is nine hours, the average rate of charge must be 8
amperes.
If charging from a 110-volt circuit, the rate at the start
should be about 10 amperes; if from a 500-volt circuit, about 9
amperes; as, in charging from a source with constant voltage,
such as a lightning or trolley circuit, the rate into the
battery will fall as the charge progresses. This also applies
if the charging be done from a mercury arc rectifier without
attendance.
=Ques. What precautions should be taken in charging a battery out of a
vehicle?=
[Illustration: FIG. 1,129.—Interior view Northwestern storage battery.
The positive plate is of double grid construction, and the negative
plate consists of a special staggered grid. The separators used between
the plates are hard rubber, ribbed on one side so as to prevent the
positive plate from buckling. It is perforated so as to allow a free
circulation of the electrolyte and to decrease the internal resistance.
Rubber separators are better than the commonly used wood or paper
separators because they prevent local action. The flat side of each
separator is placed against a positive plate, preventing shedding or
jolting of the active material of the plate. This checks deterioration.
The jars are made of rubber composition; the walls are thick and the
covers well fitted to avoid spilling the electrolyte. All Northwestern
batteries are contained in rubber composition jars. The walls are thick
and the covers fit tightly to prevent spilling the acid. A hard wood
box, treated with a moisture repellant is used for the outer case.
These batteries are made in any voltage desired, the ampere capacity
ranging from 25 amp. hrs. to 300 amp. hrs.]
Ans. When a battery is being overhauled, the cells must be connected
together in series and to the charging source in relatively the same
manner as if they were in the vehicle; that is, the positive (+)
terminal of one group of cells must be connected to the negative (-)
terminal of the next group, and the two free terminals, one positive
and the other negative, must be connected respectively to the positive
and negative terminals of the charging circuit, but not until all of
the groups have been connected in series. Great care must always be
taken to have the polarities correct and the wire or cable for the
connections of ample size to carry, without heating, the heaviest
current used in charging.
=Charging Small Cells.=—For cells of the portable type, having
capacities from 10 to 100 ampere hours, the normal charging and
discharging rate should be about one-tenth the stated capacity, but
the discharging rate may be increased to double this value, in case of
necessity.
If the cells be provided with formed plates and not charged, the jars
should be filled with the proper electrolyte, and then charged for at
least 10 hours steady, or until they boil, then they may be discharged.
In the case of unformed plates, the charging should be from 30 to 40
hours, until the cells boil, and the plates assume their proper color.
=Ques. How are small cells easily charged from 110 or 220 volt
circuits?=
Ans. This may be conveniently done by inserting in one of the charging
leads an incandescent lamp which will pass the required quantity of
current. If the current required be as large as 10 amperes, a suitable
resistance or 10 lamps in parallel, each passing one ampere, may be
used. Great care should be taken to see that the battery is connected
properly.
=Period of Charging a New Battery.=—In the case of batteries provided
with formed plates, the first charge should extend over a period of
not less than 30 consecutive hours, without stopping, if possible,
or for periods of not less than 10 hours a day for three consecutive
days. The electrolyte will then commence to "boil" or "gas," assuming
a milky appearance due to the ascending bubbles of gas. At this stage
the density of the electrolyte as shown by the hydrometer placed in
each cell should be at least 1.200; it is essential that the charging
should be continued until every cell boils equally. From this point the
charging should be prolonged until the pressure, as determined by a
voltmeter or a cadmium tester, rises to about 2.55 volts.
[Illustration: FIG. 1,130.—The Willard underslung battery box for
automobiles. The general tendency in automobile design, is to keep
everything off the running board as far as possible, and to get tool
boxes, battery boxes, etc., placed somewhere under cover. To meet
these conditions the box here illustrated is arranged so that it can
be underslung beneath the rear footboard or supported on auxiliary
cross members made of strap iron and attached to the side members of
the chassis. It is usually suspended under the rear footboard or the
rear seat. The box has a chemically treated wood lining to make it
acid proof. The lining is so made that there is air space between the
battery and the sides of the box, except at the corners. Ventilation
is thus obtained and the battery kept dry. Accumulation of water or
spilled electrolyte in the bottom of the box is prevented by grooves in
the bottom board, extending downward from the corners to an outlet at
the center of the board. The box is also fitted with rubber bushings in
the holes where wire leaves the battery box.]
The charging of unformed plates is similar in all respects to
that of formed plates, except that the first charging should
extend over a period of at least 70 consecutive hours without
stopping, at the end of which time the plates should have the
characteristic colors of those of a fully charged battery. If
they do not, the charging should be prolonged and the cell
tested for density of electrolyte, and voltage, as already
described until the desired conditions are attained. Then the
battery may be discharged and recharged.
It is probable that a total of 300 to 400 hours of charging
with intervening discharges will be required to form the
plates until they acquire a good color, and the density of the
electrolyte becomes stable.
In regular charging, the rate should be rapid when the battery is
nearly exhausted, but it should be greatly reduced at the end of the
charge after passing the point of boiling. Charging at too low a rate
is always injurious.
=Ques. What may be said with respect to the capacity of a new battery?=
Ans. A new battery will never give its full capacity till after about
twenty discharges. During this time it should be given about 25%
overcharge. After that, 10% overcharge, that is, 10% more charge than
was taken out, will be sufficient for ordinary work.
=High Charging Rates.=—Occasionally it is desirable to charge a
battery as quickly as possible. As a general rule, such a procedure
should not be adopted unless the battery be thoroughly discharged, and
not then, unless done by a person who thoroughly understands what he is
about; battery makers will always furnish data and directions to meet
emergencies.
In charging a battery at a high rate, the danger to be avoided
is the tendency of the cells to heat. The troubles that might
arise from this cause may be prevented by immediately reducing
the current strength. The proper rate of charge for a given
battery of cells may be thus discovered by experiment. A
battery should never be charged at a high rate unless it be
completely exhausted, since it is a fact that the rate of
charge that it will absorb is dependent upon the amount of
energy already absorbed.