Cyclopedia of Telephony and Telegraphy, Vol. 2 / A General Reference Work on Telephony, etc. etc.

by American School of Correspondence

Initial Charge. As soon as the plates have been installed in the tanks and welded to the bus bars, the cell should be filled with electrolyte having a specific gravity of 1.180 to 1.190 to one-half inch above the tops of the plates and then the charge should be immediately started at about the normal rate. In the case of a battery consisting of cells of large capacity, it is customary to place the electrolyte in the cells as nearly simultaneously as possible rather than to completely fill the cells in consecutive order. When the electrolyte is placed in the cells simultaneously, the charge is started at a very much reduced rate before the cells are completely filled, the rate being increased as the cells are filled, the normal rate of charge being reached when the cells are completely filled. Readings should be taken hourly of the specific gravity and temperature of the electrolyte, voltage of the cells, and amperage of charging current. A record or log should be kept of the specific gravity and voltage of each of the cells of the battery regularly during the life of the battery and it is well to commence this record with the initial charge.

The initial charge should be maintained for at least ten hours after the time when the voltage and specific gravity have reached a maximum. If for any reason it is impractical to continue the initial charge uninterrupted, the first period of charging should be at least from twelve to fifteen hours. However, every effort should be made to have the initial charge continuous, as an interruption tends to increase the time necessary for the initial charge, and if the time be too long between the periods of the initial charge, the efficiency and capacity of the cells are liable to be affected. In case of a large battery, precaution should be taken to insure that the ventilation is exceptionally good, because if it is not good the temperature is liable to increase considerably and thereby cause an undue amount of evaporation from the cells.

The object of the temperature readings taken during the charge is to enable corrections to be made to the specific gravity readings as obtained by the hydrometer, in order that the correct specific gravity may be ascertained. This correction is made by adding .001 specific gravity for each three degrees in temperature above 70° Fahrenheit, or subtracting the same amount for each three degrees below 70° Fahrenheit. At the time the cells begin to gas they should be gone over carefully to see that they gas evenly, and also to detect and remedy early in the charging period any defects which may exist. If there is any doubt in regard to the time at which the cells reach a maximum voltage and specific gravity, the charge should be continued sufficiently long before the last ten hours of the charge are commenced to eliminate any such doubt, as in many cases poor efficiency and low capacity of a cell later in its life may be traced to an insufficient initial charge.

Operation. After the battery has been put in commission the periodic charges should be carefully watched, as excessive charging causes disintegration and decreases the life and capacity of the battery; while, on the other hand, undercharging will result in sulphating of the plates and decrease of capacity, and, if the undercharge be great, will result in a disintegration of the plates. It is, therefore, essential that the battery be charged regularly and at the rate specified for the particular battery in question. In order to minimize the chance of either continuously overcharging or undercharging the battery, the charges are divided into two classes, namely, regular charges and overcharges. The regular charges are the periodic charges for the purpose of restoring the capacity of the battery after discharge. The overcharges, which should occur once a week or once in every two weeks, according to the use of the battery, are for the purpose of insuring that all cells have received their proper charge, for reducing such sulphating as may have occurred on cells undercharged, and for keeping the plates, in general, in a healthy condition. The specific gravity of the electrolyte, the voltage of the battery, and the amount of gasing observed are all indications of the amount of charge which the battery has received and should all be considered when practicable. Either the specific gravity or voltage may be used as the routine method of determining the proper charge, but, however, if the proper charge is determined by the voltage readings, this should be frequently checked by the specific gravity, and vice versâ.

During the charging and discharging of a battery the level of the electrolyte in the cells will fall. As the portion of the electrolyte which is evaporated is mainly water, the electrolyte may be readily restored to its normal level by adding distilled water or carefully collected rain water.

Pilot Cell. As the specific gravity of all the cells of a battery, after having once been properly adjusted, will vary the same in all the cells during use, it has been found satisfactory to use one cell, commonly termed the pilot cell, for taking the regular specific gravity readings and only reading the specific gravity of all the cells occasionally or on the overcharge. This cell must be representative of all the cells of the battery, and if the battery is so subdivided in use that several sets of cells are liable to receive different usage, a pilot cell should be selected for each group.

Overcharge. If the battery is charged daily, it should receive an overcharge once a week, or if charged less frequently, an overcharge should be given at least once every two weeks. In making an overcharge this should be done at a constant rate and at a rate specified for the battery. During the overcharge the voltage of the battery and the specific gravity of the pilot cell should be taken every fifteen minutes from the time the gasing begins. The charge should be continued until five consecutive, specific-gravity readings are practically the same. The voltage of the battery should not increase during the last hour of the charge.

As the principal object of the overcharge is to insure that all of the cells have received the proper charge, it must, therefore, be continued long enough to not only properly charge the most efficient cells, but also to properly charge those which are lower in efficiency. The longer the interval between overcharges, the greater will be the variation between the cells and, therefore, it is necessary to continue the overcharge longer when the interval between overcharges is as great as two weeks. Before the overcharge is made the cells should be carefully inspected for short circuits and other abnormal conditions. These inspections may best be made by submerging an electric lamp in the cell, if the cell be of wood, or of allowing it to shine through from the outside, if it be of glass. By this means any foreign material may be readily detected and removed before serious damage is caused. In making these inspections it must be borne in mind that whatever tools or implements are used must be non-metallic and of some insulating material.

Regular Charge. Regular charges are the periodic charges for restoring the capacity of the battery, and should be made as frequently as the use of the battery demands. The voltage of the cells is a good guide for determining when the battery should be recharged. The voltage of a cell should never be allowed to drop below 1.8 volts, and it is usually considered better practice to recharge when the battery has reached 1.9 volts. If a battery is to remain idle for even a short time, it should be left in a completely charged condition.

The regular charges for cells completely equipped with plates should be continued until the specific gravity of the pilot cell has risen to five points below the maximum attained on the preceding overcharge, or, if only partially equipped with plates, until it has risen to three points below the previous maximum. The voltage per cell at this time should be from .05 volts to .1 volts below that obtained on the previous overcharge. At this time all the cells should be gasing, but not as freely as on an overcharge.