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other, and this lamp-bank in turn placed in series with the battery, will allow a "trickling charge" of 1 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.
It will be noted in this diagram that the regular charging equipment consists of a variable rheostat, connected in circuit with the main current supply lines, for regulating the charging current to correspond with the prescribed “starting” and “finishing” rates for the particular types of battery used in the installation. Connections to ammeter and voltmeter are also shown in the diagram.
Charging and discharging are effected by means of the doublepole double-throw switch S, which may be closed on either side of the circuit, as desired. Manifestly, when discharging the battery, the double-pole snap-switch on the “trickling charge” circuit should be in the “open ” position; also, when the battery is receiving a "trickling charge” switch S should be thrown in the “open” position.
In conclusion it is safe to say that the storage battery has come to stay in our naval service, and the “trickling charge” will accordingly occupy a prominent place in the operation, care and maintenance of these batteries.