company! And if it shuts in thick, a careful course is more than ever essential. For nearly five hours the operation goes on, each ship taking up the planting as another leaves off. Darkness descends, but your neighbor shows you no "light in the window." He is just a black mass. The compass is the thing now. A flash from a blinker tube from ship to ship and the job is done. We go "ships right" off the field and take up the route formation for home. Spirits are lighter, speeds are better, and the 200-mile run to port is a jaunt. Let the "sub" on watch in The Hole have a go at us now, who cares? But he will not; he is not a sport. At early daylight we part company off Cromarty Whistler and the race for assigned berths is on. If it has been your pleasure-and duty-to be on the bridge for two days and nights on end, chilled, soaked, muscle-sore, and hungry, and your ship gets a line to the buoy, can you a second later be in your bunk, hunger forgotten, the world forgotten, fast asleep? You know what I mean! [COPYRIGHTED] U. S. NAVAL INSTITUTE, ANNAPOLIS, MD. THE "TRICKLING CHARGE" AS APPLIED TO By LIEUT. COMMANDER LUCIUS C. DUNN, U. S. Navy The chemical action which manifests itself in the storage battery cell and the normal cycle of life of this cell may be said to be analogous in many respects to that of the human body; that is, there is a constant wearing away and building up of tissues with a gradual lapse into debility and old age after a more or less definite period of activity. Moreover, just as the human body requires food, water, exercise and a reasonable amount of care and attention to preserve it in a vigorous, healthy condition for performing its characteristic functions of life, so does the storage battery also require, in effect, food, water, exercise and a reasonable amount of attention to enable it to efficiently perform its designated functions. The application of the storage battery to the art of electrical engineering in our naval service is daily increasing at an unprecedented rate, so much so, in fact, that there is now a storage battery stand-by installation designed for practically every electrical circuit on board ship, and, in many instances, the storage battery constitutes the prime source of power for some of those circuits; also, in addition to the application of the storage battery on board ship, it is extensively used for similar purposes on shore stations and in the aviation branch of our service. Therefore, in order that these storage batteries may receive the proper care and attention which they deserve, thereby insuring that they will efficiently perform the various duties required of them when called upon, it is essential that our personnel 66 charged with the operation, care and maintenance of these batteries duly appreciate the foregoing analogy and bear in mind that there is a certain amount of human nature" even in a storage battery. This done, it is believed that the sphere of usefulness of the storage battery will be further increased and that it will prove a stepping-stone to even greater achievements in the now rapidly developing art of electrical engineering in our naval service. A very necessary routine practice in the care and maintenance of the storage batteries designed for the various duties of our naval service, and a practice which should be encouraged to the end that these batteries may always be maintained in the prime of condition and ready for instant duty, is known as the "trickling charge," and it is the purpose of this article to attempt an explanation of the salient principles upon which this practice is based, as well as to describe the methods by which it may be applied to the storage batteries under regular service operating conditions on board ship and in the general naval service. "TRICKLING CHARGE" DEFINED It is well at this point to define the term "trickling charge"; it may be defined as follows: 66 When the storage battery is connected across the electrical supply mains or bus-bars and the conditions obtain wherein the battery is at all times receiving just enough current to counteract local action and thus maintain it in a full charged condition, the storage battery is said to be receiving a trickling charge." A fraction of an ampere only, the amount of which depends upon the size of the battery, is required for this "trickling charge," and, aside from the advantages obtained as a result of counteracting local action in the cell, the battery at all times has its entire capacity available for instant use when required. In other words, the small amount of charging current passing or "trickling" through the battery is just sufficient to reduce the small layer of lead-sulphate (PbSO1) normally formed in the plates as a result of the local action incident to the "internal or self-discharge" of the battery, and, furthermore, this small amount of charging current is not sufficient to cause any deleteri ous effects through heating or undue gassing of the battery. In fact, when the "trickling charge" is properly conducted practically no rise in temperature is apparent, and there is only a slight amount of gas evolved, if any. In order that a thorough understanding may be had as to the object of the "trickling charge," it is well in the beginning to consider the prime constituents of the lead-acid storage battery cell and the fundamental equation of the reactions which take place in this cell during the cycle of charge and discharge. FUNDAMENTAL EQUATION OF THE LEAD-ACID STORAGE BATTERY CELL The active constituents of the lead-acid storage battery cell are as follows: (a) Positive plate; lead-peroxide (PbO2), which is of a velvety "chocolate" brown color. (b) Negative plate; finely divided sponge lead (Pb), which is of a "battleship" gray color. (c) Electrolyte; dilute sulphuric acid (H2SO), consisting of chemically pure sulphuric acid diluted with pure distilled water. The generally accepted fundamental equation for the normal chemical action which takes place in this cell may be thus indicated as follows: Pb+ PbO2+2H2SO,; cell in charged condition. Therefore, in combining the above, the fundamental equation of the complete reaction is written as follows: Pb+PbO2+2H2SO (✈) 2PbSO1+2H2O. In other words, the conventional sign () indicates that this reaction is completely reversible; that is, reading this equation from left to right (→) denotes the action which takes place during discharge of the cell, and reading from right to left (<), that which takes place during charge. It is, therefore, apparent from the above equation that during discharge the acid radical, SO,, of the electrolyte combines with the active materials of the positive and negative plates and converts both of these plates into lead-sulphate (PыSO1). More over, during charge the lead-sulphate is reduced by the charging current and the acid radical returned to the electrolyte, the active materials of both plates being accordingly restored to their original states; that is, to sponge lead and lead-peroxide. SELF-DISCHARGE OF AN IDLE BATTERY It is an established fact that if a fully charged or a partially charged battery is allowed to stand idle long enough it will eventually become completely discharged of its own accord. This is manifested by a reduction in the cell voltage, a drop in the specific gravity of the electrolyte and the formation of leadsulphate in the positive and negative plates. In other words, although the circuit connecting the terminals of the battery has not been closed during the idle period and, consequently, no current drawn from the battery, the acid radical of the electrolyte has nevertheless combined with the active materials of both sets of plates, converting them into lead-sulphate in the same manner as though the battery had been subjected to a regular useful service discharge. A fully charged battery will completely discharge itself in approximately 100 days if allowed to remain idle without receiving a freshening charge during this period. However, the degree of acid concentration in the electrolyte and the temperature to which the battery is subjected are governing factors in the time element required for a battery to become discharged through self-discharge, high acid concentration and high surrounding temperatures tending to lessen the time element. necessary for a complete self-discharge as outlined above. FACTORS WHICH PRODUCE SELF-DISCHARGE There are several factors which are in various degrees responsible for the internal or self-discharge which takes place in an idle storage battery. These factors, when considered either individually or collectively, are, in battery parlance, usually referred to under the general term "local action." Chief among these several factors may be stated the following: 1. Impurities in the electrolyte. 2. Impurities in the materials composing the grids, and defective grid-casting. |