Standard commercial resistance units of identical rating as standard size lamps may now be obtained; these resistance units are also designed to screw into the standard incandescent lamp sockets.

All storage batteries designed for stand-by circuits on board ship, as well as spare submarine cells kept in the battery service stations on submarine tenders, should be maintained in a charged condition by the "trickling charge" method. Also, spare submarine batteries stored at navy yards for emergency installation can be kept in good serviceable condition and with comparatively little cost of upkeep and maintenance by this method, and its practice should be encouraged.

COMPUTING THE "TRICKLING CHARGE" RATE

The number of positive plates contained in the cell constitutes the basis for computing the "trickling charge" rate for a given battery installation. For the portable types of storage batteries used in the naval service and having positive plates inch in thickness a trickling charging rate of .025 ampere per positive plate has been found to be sufficient to counteract local action and maintain the plate in a fully charged, healthy condition. Thus, if such a cell contains n positive plates, the "trickling charge" rate for this cell would be nx.025 ampere.

For all portable type cells having positive plates less than inch. in thickness .0125 ampere per positive plate, or one-half of the 4-inch plate rating, should be used in absence of any other specific rating designated by the battery manufacturer. In respect to this feature, the navy specifications for portable types of storage batteries require that each storage battery manufacturer submit detailed drawings of every type cell supplied on government contracts; in addition to containing detailed drawings of parts for the information and use of the battery service stations and operating personnel in ordering spare parts, making repairs, etc., these drawings also specify the number and size of the plates installed in the cells. For submarine type cells the battery manufacturers also supply the required "trickling charge" rate for each type.

Therefore, in order to ascertain the "trickling charge" rate for a given cell or battery installation, it is only necessary to con

sult these detailed drawings supplied by the battery manufacturers. The required "trickling charge" rate should also be found on the metal name-plate attached to the cell tray.

It has also been found that the charge voltage of a cell through which is passing the required amount of "trickling charge" current averages from 2.15 to 2.20 volts. Therefore, when calculating the “trickling charge " rate for a given installation if 2.15 volts per cell is used the results will be sufficiently accurate for practical application.

Example. The storage battery charging busses on board ship are connected across the 115-volt supply mains, and it is desired to place a set of auxiliary lighting batteries on "trickling charge"; each cell of this battery contains nine plates, four positive and five negative, and the entire battery consists of 12 cells, all of which are connected in series.

Find the "trickling charge" rate for this battery, and the amount of the resistance to be placed in series with the battery in order to conduct the "trickling charge" at the required rate.

Solution. This type of cell conforms to the navy standard for these batteries and contains four 4-inch positive plates. Hence, the "trickling charge" rate for this cell is:

66

Also, since there are 12 cells connected in series, the counter electromotive force produced by this battery when on trickling charge" at the required rate is:

12X2.15 volts=25.8 volts.

Therefore, 115-25.8-89.2 volts, which must be absorbed by a resistance placed in series with this battery.

R=892 ohms, the amount of the resistance to be inserted in series with the battery in order to allow a "trickling charge" of .I ampere to pass through the battery.

Therefore, in order to translate this resistance in terms of lamp-banks it is only necessary to select lamps of such rating and to so combine them that the value of the resistance offered by the entire lamp-bank will be 892 ohms; various combinations of lamps may be utilized for such a lamp-bank. For the particular problem outlined above it has been found that a bank consisting of three 25-watt metallic filament lamps placed in series with each

other, and this lamp-bank in turn placed in series with the battery, will allow a "trickling charge" of .I ampere to pass through the battery.

GASSING AND VENTILATION OF BATTERIES DURING "TRICKLING CHARGE" AND CARE OF COMPARTMENT IN WHICH

THEY ARE LOCATED

Although, as has been stated, when, the "trickling charge" is properly conducted, the amount of gas evolved from the storage batteries is relatively small, yet, as a precaution during this charge, the trays of these batteries should be left uncovered and the compartment in which they are located should also be well ventilated, periodically, at least, in order that any gas which is evolved will be dissipated before an explosive mixture is formed.

In this regard, tests conducted are conclusive that a 4 per cent mixture of hydrogen in air is dangerous and it is the established policy in operating storage batteries requiring forced ventilation in our service, such as the submarine types, to design the ventilating apparatus on a basis of sufficient capacity to keep the amount of hydrogen present in the air at any instant below 2 per cent, thus insuring a substantial factor of safety in the operation of these batteries.

The compartment in which the batteries are located should be kept free from sweating and otherwise as dry as possible in order to reduce the likelihood of moisture grounds occurring around the batteries. The tops of the cells, sides and tops of the trays, stowage racks, etc., should also be kept dry and free from acid spray, as in addition to causing leakage between the cell terminals and other such grounds, the cell trays and other woodwork around the batteries will become acid soaked, which will eventually result in rotting of the woodwork of the trays and other parts. It is good practice to give the cell trays and other woodwork around the batteries a coating of asphaltum or other acid-resisting paint periodically as necessary. All metal work in the compartment in which the batteries are installed should also be coated with acid-resisting paint to protect them from the corrosive action of the acid fumes and spray given off from the batteries. It is essential to successful operation of the batteries

that the compartment be kept clean and no metals, tools or other materials stored around or on top of the batteries.

WATERING BATTERY AND ROUTINE OVERCHARGE

In conducting the "trickling charge," the cells should be watered regularly with pure distilled or other approved battery water to replace that lost in evaporation. Under no conditions should acid be added to replace evaporation.

Also, for best results, the battery should, as a routine practice, be given an "overcharge" at the prescribed "finishing" rate at least once a month in order to thoroughly mix the added water with the electrolyte and to prevent the injurious effects of stratification of the acid in the electrolyte. In this regard, cells which are allowed to remain inactive for protracted periods, that is. not being subjected to regular cycles of charge and discharge, are subject to this acid stratification in the electrolyte, in that the heavier and more concentrated acid tends to settle to the bottom of the cell with the result that effect of local action on the plates is more pronounced in the lower part of the cell. Although, as has been pointed out, the "trickling charge" is designed to reduce the effect of local action to a minimum, the trickling charge" rate is not sufficient to produce enough gassing in the cell to stir up or agitate the electrolyte, and for this reason the periodic overcharge is helpful in dissipating any tendency to stratification of the acid.

The duration of this overcharge should be sufficiently long to insure that a maximum specific gravity reading has been obtained, as shown by four successive readings taken at equal intervals for a period of one hour. Such a maximum gravity reading insures that practically all acid has been driven out of the plates, if the cells have received the proper attention during previous operation.

There is shown in Fig. 2 a composite wiring diagram of the complete equipment required for charging or discharging a set of storage batteries on board ship. In addition to the "trickling charge" equipment which has already been described, this diagram also includes the necessary connections and equipment for giving the storage battery a normal charge, and "overcharge," as well as the connections for discharging the battery through the discharge service lines.