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:

For quick charging in three hours the rates should be: 50 per cent. 1st hour; 33¹/₃ per cent. 2nd hour; 16²/₃ 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:

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.

The vibrating armature of each unit is divided into two parts, which gives flexibility, affords increased current capacity and minimizes sparking, the two leads shown being connected together in one circuit.

A primary relay and a secondary switch (E and F, figs. 1,154 and 1,156), close their contacts when current is flowing.

Upon failure of the main alternating current line they operate to open the charging circuit. A storage battery is thus prevented discharging through the rectifier.

Upon resumption of the main alternating current, the rectifier starts automatically.

Every battery room should be provided with a water tap and sink. The floor should be paved with vitrified brick, preferably blue or yellow in color, of diamond pattern and sloping in all directions toward suitable drains. A floor of this type can be easily washed by flooding with water, and its patterns tend to keep it dry under foot at all times. Wooden floors are rotted very quickly by acid spillings and by the spray.

The room should be kept absolutely clear of everything, which may be injured, by the sulphuric acid fumes and it should be well ventilated to insure the safety and good health of the attendants.

A battery, even at rest, gives off hydrogen which when diluted with air forms a mixture which is very liable to explode if brought in contact with any kind of flame. Unless proper ventilation be provided, the breaking of the connection when a current is flowing, or the lighting of a bare flame lamp in the battery room would be dangerous.

Battery Attendants and Workmen.—Those employed in setting up batteries are liable to suffer from soreness of hands and the destruction of clothing unless proper precautions be taken to prevent the same. In order to avoid these troubles, the boots should be painted with paraffine mixed with an equal quantity of beeswax.

The clothing should be of woolen material, which, unlike cotton, is practically unaffected by the acid. If cotton shirts be worn, they should be dipped in a strong solution of washing soda and then rough dried.

An apron of sacking, backed with flannel should be worn over all the other clothes. A bottle of strong ammonia should be kept in the battery room at all times, and in case of an accidental splash of acid on the clothes, the immediate application of a small quantity of the ammonia, by means of the stopper, will at once neutralize the acid and prevent it burning a hole in the material. A pail containing water made strongly alkaline with washing soda should also be kept conveniently at hand during all operations in the battery room. The hands should be dipped occasionally in this water in order to prevent the skin smarting and becoming sore under the action of the acid.