THE "B" BATTERIES

Radio Record, Volume I, Issue 42, 4 May 1928, Page 15

THE "B" BATTERIES

WHEN TO DISCARD THEM. Failures in wireless receivers are being traced daily to the discharge of the high-tension (‘‘B’’) battery. The lowtension (‘A’) battery is :*®.ays under observation, because, unless it is fully charged, the valves do not light to customary brilliancy. It is, therefore, a. simple matter to judge when it needs recharging, by noting the condition ot | the valve filaments, although this method is not recommended as a scientific test, There is no corresponding crnde test which can be applied to the hightension battery, and its condition therefore often escapes attention. The only satisfactory method of testing a hightension battery is by the use of a voltmeter, High-tension voltmeters are now so cheap that one should form part of the equipinent with every valve receiver. It is worth remembering, however, that some of the cheaper hightension voltmeters are badly designed, in that they impose a rather heavy drain on the battery undergoing test. They should therefore be used as little as possible, and left on the battery only long enough to obtain an accurate reading, It will usually be found that the pressure of a high-tension battery will fall off fairly steadily until

it has dropped to about four-fifths its original voltage. When Trouble Starts. After that point is reached, the battery becomes noisy, and it is likely to be unreliable, as the voltage may fall without warning to twv or three volts. Thus, it is generaily wise to discard a high-tension battery when it has been used nutil its voltage has dropped to 86 in the case of a 45-volt block, or 18 in the case of a 224-volt block. In ordinary circumstances the life of the battery to this point should be between three months and a year or more, depending on conditions of use. If a sudden battery failure occurs before the battery is about three months old, it is likely to be due to the failure of one section. Most batteries are now divided off by terminals into sections of different voltages, and these sections can be tested one after the other by the voltmeter. When the defective section is found it can be bridged over by a piece of wire so that it is removed from the circuit, and the battery will then probably last for manw weeks longer, giving a slightly lower pressure, of course, than if one section had not failed.