Chapter XLIV: Storage Batteries (1)

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=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.

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.

=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.

=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.

=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.

=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.

=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.

=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.

=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.

=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.

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.

=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.

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.

=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.

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.

=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.

=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.

=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.

=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.

=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.

=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.

=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.

(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.

=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.

=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.

=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".

=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?=

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.

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.

For rapid charging, when a battery has to be charged in four hours, the current should vary about as follows:

40 per cent. of total 1st hour
25 " " " " 2nd "
20 " " " " 3rd "
15 " " " " 4th "

For quick charging in three hours the rates should be: 50 per
cent. 1st hour; 33⅓ per cent. 2nd hour; 16⅔ per cent. 3rd
hour.

=Mercury Arc Rectifier.=—This is a device for obtaining direct current from alternating current for use in charging storage batteries. The transformation is obtained at a low cost, because the regulation is obtained from the alternating side of the rectifier, while the current comes from the direct current side.

The theory is as follows: In an exhaust tube having one or more mercury electrodes, ionized vapor is supplied by the negative electrode or cathode, when the latter is in a state of "excitation." This condition of excitation can be kept up only as long as there is current flowing toward the negative electrode.

If the direction of the voltage be reversed, so that the formerly negative electrode is now positive, the current ceases to flow, since in order to flow in the opposite direction it would require the formation of a new negative electrode, which can be accomplished only by special means. Therefore, the current is always flowing toward one electrode—the cathode, which is kept excited by the current itself. Such a tube would cease to operate on alternating current voltage after half a cycle if some means were not provided to maintain a flow of current continuously towards the negative electrode.

=Ques. Describe the construction and operation of a mercury arc rectifier.=

Ans. Fig. 1,135 is an elementary diagram of connections. The rectifier tube in an exhausted glass vessel in which are two graphite anodes A, A´, and one mercury cathode B. The small starting electrode C is connected to one side of the alternating circuit, through resistance; and by rocking the tube a slight arc is formed, which starts the operation of the rectifier tube. At the instant the terminal H of the supply transformer is positive, the anode A is then positive, and the arc is free to flow between A and B. Following the direction of the arrow still further, the current passes through the battery J, through one-half of the main reactance coil E, and back to the negative terminal G of the transformer. When the impressed voltage falls below a value sufficient to maintain the arc against the reverse voltage of the arc and load, the reactance E, which heretofore has been charging, now discharges, the discharge current being in the same direction as formerly. This serves to maintain the arc in the rectifier tube until the voltage of the supply has passed through zero, reversed, and built up such a value as to cause the anode A to have a sufficiently positive value to start the arc between it and the cathode B. The discharge circuit of the reactance coil E is now through the arc A'B instead of through its former circuit. Consequently the arc A'B is now supplied with current, partly from the transformer, and partly from the reactance coil E. The new circuit from the transformer is indicated by the arrows enclosed in circles.

=Ques. How is a mercury arc rectifier started?=

Ans. A rectifier outfit with its starting devices, etc., is shown in figs. 1,132 to 1,134. To start the rectifier, close in order named line switch and circuit breaker; hold the starting switch in opposite position from normal; rock the tube gently by rectifier shaker. When the tube starts, as shown by greenish blue light, release starting switch and see that it goes back to normal position. Adjust the charging current by means of fine regulation switch on the left; or, if not sufficient, by one button of coarse regulation switch on the right. The regulating switch may have to be adjusted occasionally during charge, if it be desired to maintain the charging current approximately constant.

=Capacity.=—The unit of capacity of a storage cell is the _ampere hour_, that is, the ability to discharge one ampere continuously for one hour. For instance, a 100 ampere hour battery will give a continuous discharge of 12½ amperes for eight hours. It should theoretically give a discharge of 25 amperes continuously for four hours, or 50 amperes for two hours, but in reality, the ampere hour capacity decreases with an increase of discharge rate.

It requires, theoretically .135 ounces of metallic lead on either element reduced to sponge lead or to lead peroxide to produce one ampere hour; in practice, from four to six times this amount is required.

The reason for this is because it is impossible to reduce all
the active material, to bring every particle in contact with
the electrolyte, or to cause every part to be penetrated by the
current.

Experiments show that from .5 to .8 ounces of sponge lead, and from .53 to .86 ounces of metallic lead converted into peroxide, are required on their respective elements to produce a discharge of one ampere hour at ordinary commercial rates.

The capacity increases with the temperature, being about one per cent. for each degree Fahr. increase in temperature.

Battery capacity depends on the size and number of plates; the quantity of active material present, and the quantity of electrolyte.

For an eight hour rate of discharge and 60 degrees temperature, the capacity of American batteries varies from 40 to 60 ampere hours per square foot of positive plate surface ( = 2 × number of positive plates in parallel × length × breadth).

The following table gives the variation of capacity for different rates of discharge:

Capacity Variation for Different Discharge Rates

+——————————-+——————————————————————+
| Discharge | Per cent of capacity |
| rate | at 8 hour rate |
+——————————-+——————————————————————+
| | =Plante= | =Faure= |
| 8 hour | 100% | 100% |
| 6 hour | 96% | 96% |
| 4 hour | 80% | 88% |
| 2 hour | 61% | 70% |
| 1 hour | 56% | 48% |
+——————————-+——————————+——————————-+

=Ques. How may the capacity of a battery be increased?=

Ans. By mixing organic materials with the lead oxide, _but any such mixture is always accompanied by a rapid deterioration of the plates_.

=Discharging.=—In discharging a battery its voltage should never be allowed to fall below 1.8 volts, under load, thus leaving about 30 per cent. of the total capacity unused. The normal discharging current may be equal to the normal charging current, but a discharge equal to 3 or 4 times the normal may be given without injury to the plates. Some types may be discharged at even six or seven times the normal rate. In such cases, however, the capacity will be reduced in the same proportion, as before explained in the paragraph dealing with battery capacities.

=Ques. What is the effect of discharging too rapidly?=

Ans. It tends to break the plates, and in the case of pasted plates, a very sudden discharge will dislodge the paste.

=Ques. How is the discharge capacity of a storage battery stated?=

Ans. In ampere hours. This, unless otherwise specified, refers to its output of current at the eight hour rate. Most manufacturers of automobile batteries specify only the amperage of the discharge at three and four hours. Thus, at the eight hour rate, a cell which will discharge at ten amperes for eight hours is said to have a capacity of eighty ampere hours. It does not follow that eighty amperes would be secured if the cell were discharged in one hour. It is safe to say that not more than forty amperes would be the result with this rapid discharge.

As a general rule, the one hour discharge rate is four times
that of the normal, or eight hour discharge, and considerations
of economy and prudence suggest that it should never be
exceeded, if, indeed, it ever be employed. The three hour
discharge, which is normally twice that of the eight hour,
is usually the highest that is prudent, while the four hour
discharge is the one most often employed in vehicles for the
average high speed riding.

=Ques. What should be the maximum rate of discharge?=

Ans. The one-hour rate; this when used, should not extend over fifteen or twenty minutes. In the case of regulating batteries a forty-five minute rate of discharge may be allowed for one or two minutes during great fluctuations of load.

=Ques. How does the capacity decrease?=

Ans. It decreases with the increase in current output.

An 80 ampere hour cell, capable of delivering 10 amperes for 8
hours, would, when discharged at 14 amperes, have a capacity of
70 ampere hours; when discharged at 20, its capacity would be
60; and when discharged at 40, its capacity will have decreased
from 80 to 40 ampere hours.

=Ques. What, in general, are the indications of the quantity of electricity remaining within a cell?=

Ans. The voltage, and the density of the electrolyte.

=Ques. What should be done after discharging?=

Ans. Whenever possible the battery should be immediately charged.

=The Battery Room.=—Precautions should be taken to prevent any direct sunlight falling on the battery cells in glass jars, as the breakage of such jars due to unequal expansion of the different portions of the glass, is a source of constant trouble and danger.

The exclusion of direct sunlight also tends to keep the evaporation of the electrolyte at a minimum.

Operation of Edison Rectifier

The operation of the Edison rectifier may be explained as
follows with the aid of figs. 1,154 to 1,156 (the parts being
uniformly lettered in the figures): The primary circuit taken
from the alternating current mains by the cord B, embraces the
primary winding of the transformer T, a condenser C, and the
coils P, of the vibrating units, fig. 1,155.

The secondary circuit from the transformer embraces the
massive carbon and copper contacts (N and O, fig. 1,156) which
pass only the positive waves of the alternating current, for
charging batteries or other duty.

An ammeter and rheostat may be placed in this charging circuit
if the current is to be varied, or a fixed connection may be
substituted on the base of the rectifier if it is to be used
for the maximum duty of 8 or 16 amperes.

The vibrating unit (fig. 1,155), which operates in a manner
similar to the well known action of a polarized relay, includes
a permanent magnet M; the coil in the primary circuit P; the
vibrating armature of steel with removable carbon contact N;
the stationary copper contact with comb top for heat radiation
O, and the screw Q for adjusting the amplitude of the armature
vibration.

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Hawkins Electrical Guide v. 04 (of 10)Chapter XLIV: Storage Batteries (1)

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