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3. Local couples formed in the manufacture of the positive

plates.

4. Local couples formed in the manufacture of the negative

plates.

5. Leakage of current between the cell terminals as a result of moisture grounds, etc.

Each of the above factors may be briefly commented upon as follows:

Impurities in the Electrolyte.-As a general rule any metallic impurities present in the electrolyte will cause a loss of charge at the negative plates. During charge such metallic impurities are deposited upon the negative plates where they form innumerable local couples with the active materials of these plates, with the consequent result that in the presence of the electrolyte discharge takes place, thus liberating hydrogen at the negative plates and with a loss of charge at these plates.

Such metallic impurities include antimony, arsenic, copper, iron, platinum and tin. Iron is in general the most active and destructive of the above-mentioned impurities, for due to the fact that the ions of this metal can exist in two different stages of oxidation, each stage of which is capable of being converted from one to the other, these ions continually oscillate from one group of plates to the other, when the cell is placed on open circuit, thus causing a consequent loss of charge at each group.

It requires only a comparatively small amount of iron in a cell to completely discharge it in a very short while when the cell is left on open circuit. Therefore, great care should be exercised when operating the storage battery that iron is prevented from entering the cell, such as through using electrolyte or water which contains iron, dropping into the cell iron nuts, bolts, washers, nails, tools, etc., or through any other cause. Furthermore, all iron which enters a cell from time to time is cumulative in effect, as none of this metal is lost by electrolytic decomposition or liberated in a gaseous state, as is the case with certain other impurities.

Impurities in the Materials Composing the Grids, and Defective Grid-Casting.-The alloy used in casting the grids of the storage battery cell consists of lead and antimony. If these metals are not refined to a very high degree the other metallic impurities contained will set up small local couples in the

presence of the electrolyte, thus causing a loss of charge of the plates. Also, if the lead-antimony alloy is not a homogeneous mixture or if there are segregations of pure antimony and pure lead in spots with blow-holes or shrinkage cracks in the casting as a result of improper cooling or insufficient mixing of the alloy before pouring into the molds, other local couples are formed, which accounts for a further loss of charge of the plates. Local Couples Formed in the Manufacture of Positive Plates. As outlined above, the grids are composed of leadantimony alloy, whereas the active material of the positive plates consists of lead-peroxide. We thus have a couple formed by the lead-peroxide and the grid in the presence of the electrolyte, which results in a certain amount of discharge of the positive plate, the amount of which depends upon the surface contact area between the positive active material and the grid. However, the discharge from this cause is of comparatively short duration, since a layer of lead-sulphate is eventually formed between the grid and the active material of the positive plate, thus forming an insulating medium which prevents further discharge.

Also, another source of internal or self-discharge of the positive plates, especially in the Planté type, is the failure to remove all of the forming agents which were used in forming the plates. If these plates are not thoroughly cleared of all such forming agents, the loss of charge from this cause is likely to prove quite appreciable in amount.

Local Couples Formed in the Manufacture of Negative Plates. As in the case of the positive plates, we have in the negative plates local couples formed by the lead-antimony alloy grid in contact with the sponge lead active material, and in the presence of the electrolyte a certain amount of discharge takes place in the negative plates from this cause. Also, as was described in the preceding paragraph relating to the positive plates, a thin insulating layer of lead-sulphate is similarly formed between the negative grid and the active material of this plate, thus preventing a further loss of charge from this cause.

Another loss of charge at the negative plate is due to the local action which takes place between the various materials used for obtaining porosity, increasing conductivity and the various expanders used in the manufacture of these plates.

Leakage of Current Between Cell Terminals.-Although, properly speaking, loss of discharge from this cause is not due to local action in the strict meaning of the term, it is nevertheless included here since it accounts for quite an appreciable amount of loss of charge in an idle storage battery cell if such a condition is allowed to exist sufficiently long without rectifying it; in fact, the loss of discharge through this cause is in some cases equal to, if not greater than, the combined loss of charge due to the other factors outlined above, provided the leakage of current between the terminals is of protracted duration.

METHOD OF CONDUCTING "TRICKLING CHARGE"

Having considered the effects of the various factors of local action in producing self-discharge of the idle storage battery cell, the object of the "trickling charge" in reducing to a minimum the effects of this local action, as well as maintaining the battery in a fully charged, healthy condition is, therefore, readily apparent.

As was explained in defining the term "trickling charge" in the early part of this article, only a fraction of an ampere of current is sufficient to counteract this local action, the amount of the current depending upon the type of the battery in respect to the size and the number of plates installed in the cells.

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LAMP-BANK METHOD

A very satisfactory and simple method of conducting the trickling charge" and one which is very conveniently applied on board ship is known as the Lamp-Bank Method, and consists in connecting lamp-banks in series with the battery and the charging busses of the ship's main supply lines, the number of lamps used depending upon the following:

(a) Type of battery; size and number of plates in the cells. (b) Number of cells in the battery.

(c) Voltage of the charging busses.

The function of the lamp-banks is that of a resistance to absorb the excess voltage in the main charging line over that required for the small amount of "trickling charge" current passing through the battery.

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Fig. I contains an illustration of the equipment and necessary connections required for conducting a "trickling charge" by the lamp-bank method on navy type storage batteries.

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The lamp-banks connected in series with the battery and the main charging busses are plainly shown in this illustration, as is also the double-pole snap-switch used for cutting on or off the trickling charge" current, as desired. The direction of the current in passing through the battery on charge is as indicated by the arrows in the drawing. In this regard, as in all other cases of charging storage batteries, it is essential that only direct current be used for this purpose and that the positive terminal of the battery be connected to the positive charging bus and the negative terminal of the battery to the negative bus. To do otherwise will result in serious harm to the battery.

In conducting the "trickling charge" by the lamp-bank method, the life of the lamps will be increased if the arrangement of the lamp-banks is such as to reduce the voltage sufficiently to cause the lamps to burn at a low incandescence. Also, as a general rule, on account of their high efficiency and long life, tungsten filament lamps should be used, if obtainable, in preference to carbon filament lamps, as they afford a finer degree of current and voltage regulation than the carbon filament lamps. However, if the conditions are such that it is not practicable to use tungsten filament lamps, carbon filament lamps may be used. The advantage in using lamp-banks as a resistance, instead of using regular commercial resistance units in conjunction with a low-reading ammeter, rests in the fact that lamp-banks at all times afford a reliable visual indication that current is “trickling" through the battery, whereas, the needle of the ammeter does not present so striking an indication of the charging current ; in other words, as long as the lights are burning it is definitely known that current is passing through the battery, and anybody on watch in the vicinity, whether he be a coal-passer or an ordinary seaman, can tell when the charging current is on or off.

At navy yards, shore stations and regular battery service stations, where the organization is such that someone is in constant attendance with the storage batteries on charge, commercial resistance units may well be used in connection with ammeters and voltmeters, as at such places proper facilities are at hand for using at all times accurately calibrated instruments, etc.

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