RECTIFYING AND CHARGING

Radio Record, Volume I, Issue 14, 21 October 1927, Page 15

RECTIFYING AND CHARGING

A FEW HINTS ON TRICKLE: CHARGING When employing a trickle-charger to keep the A battery well up, it is not advisable for the A battery to be of large ‘€apacity. ‘The usual trickle-charger supplies a current somewhere around half am ampere, and if a large battery is in use and once gets down, such a comparatively small current would never recharge the battery, because charging time between sessions of listening-in would not be long enough for the charger to gain. In such a case the battery might be in an almost discharged state for some considerable time before the trouble was noticed, and on that account deteriorating rapidly, with at least a tendency to sulphating. With an A battery of from 15 to 20 ampere hours capacity such a position would be less likely to happen, he trickle-charger must, theoretic--ally, put back into the battery the anlount of energy that has just been used by the valve filaments, but as the time of listening will vary, and different valves of a greater or less number will be used at times, the only safe plan is tu have a trickle-charger that puts back a little more than is likely to be used in one dav, as it is really a 24-hour cycle that is to be reckoned upon, Overcharging, not carried to any extreme, will not harm a battery like undercharging docs, and if the battery is fully charged every twenty-four hours, it can be relicd upon to give full filament voltage at anv time. Anybody installing a trickle-charger should keep a close eye on the battery voltage and specific gravity during the first few weeks in order to make sure that the charge is keeping pace with current consumption. A verv small shortage in the daily charge will gradually get the battery down unless a careful watch is kept, CHEMICAL RECTIFIERS. When a chemical rectifier has been constructed and its output has to be suited to charge at a suitable ampere rate and voltage, it should be borne in mind that the amount of current passed depends upon the size of the electrodes. To pass the current required for a small B battery the aluminium electrode may be very small, and may be reduced either by cutting or by covering with rubber tape, as_already mentioned in this column, The lead electrode need not be any larger than the aluminium In most cases a resistance will be introduced with the circnit, generally by means of a lamp, and this reduces both amperes and volts, The addition of further resistance may cnt the voltage down so far as to leave no working margin, but if amperage alone is to be reduced, it is done by reducing active surface of the electrodes, and this has no effect upon the voltage. Although ammonium phosphate is the most reliable rectifying solution ordinarily used, either borax or baking soda (sodium bicarbonate) may be used. A recommenfled solution is half-and-half of sodium phosphate and potassium phosphate. These three alternative solutions should be strong, but not quite up to saturation point.