Resistance for Battery Charging

Radio Record, Volume I, Issue 43, 11 May 1928, Page 12

Resistance for Battery Charging

A HANDY UNIT FOR EXPERIMENTERS

ERE is a handy regulating re-| sistance to use in conjunction with the A battery charger described on March 2. This resistance is kept connected‘up to the charger, and by means of the switch, all resistance may be cut out, or a suitable amount may be put into the circuit for

3 charging small cells or B_ battery cells in series-parallel, as described on April 13. The panel measures 7% by 4% inches, and may be of fibre or ebonite. A switch arm and nine contacts will be required, and the panel is drilled to take these in the position shown. The base is constructed drilled in these brass bolts are plac-

gf two pieces of 3-8in. wood, 4% by 24 and 4% by 1% respectively. The narrow strip is screwed to the back of baseboard and to the front edge of it the panel is secured by screws. Two terminals are placed in the front of the base. A couple of strips may be placed underneath at the sides, and two holes should be rrovided in the base so that the whole may be fastened to shelf or table by means of screws. THE RESISTANCES. HE resistance is provided by 28’s S.w.g. nichrome resistance wire. A size either way will serve if 28's is unprocurable. The wire is made into coils to be as compact as possible, by winding round a piece of 1-8in. brass rod to make a _ close spiral. A convenient number of contacts is nine, the one on the left being an "all out" position. The spiral may be stretched out more or les.; to determine the amount of resistance between any adjacent two stops. It is a good plan to stretch out well for the first two, so that a small amount of resistance can be put in, and allow the spiral turns to be closer on the succeeding spans, and very close on the last one. This will give a good range to suit most cases. GENERAL INSTRUCTIONS. O the top of the panel is screwed a strip of wood projecting back an amount equal to the portion on the base. A narrow strip of fibre is secured to the back edge of each of the strips, and through holes ed to hold the resistances and taps. The taps are soldered to the resistance wire when in place, the resistance wire being well cleaned where the joint is to be made. The switch contacts should be numbered, so that once the suitable position for any given purpose has been found, it can be used again without any uncertainty. Further explanation should be unnecessary, as details may be seen in the diagrams. A light type of switch arm will serve to carry 1.3 ampere, but for larger currents the switch must be of suitable heavy pattern to prevent heating. A heavier gauge of resistance wire would also be necessary to carry several amperes without undue heating. An ammeter could be conveniently mounted on the panel in the space above the switch. It must be remembered that the introduction of resistance into a charging circuit cuts down both voltage and amperes, so that only sufficient resistance can be introduced that will still leave the voltage higher than that of the cells to be charged,