RADIO BATTERIES

Radio Record, Volume I, Issue 4, 12 August 1927, Page 14

RADIO BATTERIES

DRY AND WET CELLS INTERESTING FACTS, Between the storage battery and the dry battery are four outstanding differences in operating characteristics; Virst, the storage cell is rechargeable. Following the change of lead peroxide end sponge lead to lead sulplate in the normal discharge of the cell, this lead sulphate may be converted again to the original condition of peroxide on the positives and sponge lead on the negatives by connection to a suitable source of charging current, the cell then being again ready for another period of service discharge. In other words, the discharging process is reversable, and the succeeding operations of discharge as a source of electric power supply and charge to bring back the conditions under which the storage ce]l may again furnish electric current may be repeated indefinitely until the cell wears out in service. Various Differences. The primary or dry cell, however, may act but once, continuously or intermittently, as a source of electrical current. When discharged it is useless. Second, the difference in voltage of the storage cell between the state of full charge and that of nearly complete discharge is relatively slight. ‘The voltage is well maintained under given conditions of discharge rate for the larger portion of the discharge period, dropping down less rapidly at the start and holding well up until nearly at the end. With the dry cell the voltage drops in more or jess of a straight line from beginning to end of discharge and over a considerable range.

Internal Resistance. Third, the virtual internal resistance, that is, the resistance factor which produces yariation in voltage with change in current rate, is extremely low in the storage cell. Both storage and dry cells increase in internal resistance as discharge progresses Not only is this increase in resistance less marked in the storage cell but the initial value of resistance is so low that this effect is practically nil The dry cell, however, gives a voltage somewhere near its initial voltage for only a small portion of its rated capacity in terms of rate and time and exhibits more and more as discharge progresses variation of this voltage with current change. Fourth, the storage cell has to a marked extent the property of recovery. In intermittent operation, as usual in radio service, it gives at the beginning of any short discharge period a voltage higher than that given at the end of the previous discharge, and until the interfnittent discharges have integrated nearly to the rated capacity, the storage cell gives under these conditions of intermiittent use the voltage of a nearly charged condition.

~ Why Life is Shortened. Reverting for a moment to the first outstanding characteristic of the storage cell, the type of plate used in both A and B radio batteries will give in laboratory practice from 400 to 600 cycles of charge and discharge before disintegration. This would indicate a service life in radio of mauy years. Actually, this service life is greatly shortened, due to abuse, overcharging and overdis--charging, idle periods in a discharged condition, lack of attention to the necessity of refilling to replenish evaporation and other causes. In farm lighting plants, where the same type of plate is used and the battery is given a more or less coniplete charge, usually weekly or twice a week, a service life of ten years is not unusual, and six to eight years something like the average. ‘A wood radio A battery should give dependable service over a period of at least four to six years. In our second consideration, the open circuit voltage of the storage cell of the pasted plate type may be taken as 2.15 volts at full charge and initial operating voltage at low rates as 2.1. Ralio hat/teries are usually of sufficient capacity for several «weeks’ intermittent operation. ‘The final discharge voltage may be as low as 1.80, Greatest Discharge. By far the greater portion of the discharge at radio rates, whether con-

uuuous OF iernuttent, 1s between 2.05 and 1.95 volts. The final voltage is approached only as the cell nears complete discharge. This variation from 4.05 to 1.95 represents only 5 per cent. lowering in yoltage over most of the discharge period. In comparison, the initial voltage of the dry cell, 1.5, drops ‘down from the start, going to about 1.13 at the practical end of its useful service life, a variation of 25 per cent, ‘Now, again, if partially charged at more frequent intervals than would be represented by the full discharge period, or installed with a so-called trickle charger, the available voltage of the ‘Storage cell may be considered as constant at or near the 2.1 voltage or full charge, whereas the continual.loss in voltage of the dry cell is unavoidable, Making Wet Batteries,

Storage batteries for radio service are almost universally in the lead-acid type of the so-called Faure plates, ‘These are made with grids or lattice frameworks of lead antimony alloy, on which by special machine processes are pasted mixes of lead oxides, constituting the active material. After pasting, the plates are converted respectively into positives and negatives in the forming process, that is, by continued charging. ‘lhey are then in A battery manufacture, assembled into groups: by lead burning the plate lugs to so-called post straps, then asssembled with the separators, usually of wood, Port Oxford cedar, in compartment type rubber or glass containers. Cells are joined together by lead links, integrally lead burned to the posts of the positive and negative groups, and to gas and acid tight lead bushings moulded in the rubber covers. When finished, the batteries are shipped either with the acid, charged and ready for use, or more often in what is called the add-acid type In this form the batteries are without acid, but completely charged and ready for service upon the addition of the necessary acid electrolyte. Sizes of Batteries, Radio A hatteries range {n size from 18 ampere hours capacity at four volts for some types of super-heterodyne receiving sets, and 85 ampere hours at six volts for so-called trickle charge batteries, up to the larger A sizes of 15, 933, 105 and higher ampere hour capacities. B batteries are usually in two plate types, in glass jars, of capacities 2500 to 4500 milliampere hours and in assemblies of 12, 24 and 40 cells, giving nominally 24, 48 and 80 volts, aud covering the voltage range of standard 224, 45 and multiples of these figures in dry batteries. Both the A aud B types find application in broadcasting stations as well as for home receiving sets and aimateur transmission.