A 112-VOLT B ACCUMULATOR

Radio Record, Volume I, Issue 3, 5 August 1927, Unnumbered Page

A 112-VOLT B ACCUMULATOR

SIMPLE AND EASY TO CONSTRUCT

(CONCLUDED FROM LAST WEEK.)

"tue: acid used should be pure sulphuric acid, as the small extra cost is worth while and ensures long life for the battery. Fiye of acid to twenty-one parts of distilled water is the correct proportion to use. Place the distilled water in a basin and pour the acid in gradually, stirring constantly with a glass rod. Fill the tubes by means of a hydrometer or a jug and smali glass funnel, being careful not to spill. The acid should come about fin. above the wide patt of plates. Hach tube requires about ten drams of solution, and when flie plates are not in this reaches a depth of about 3} inches. Mix 68 fluid ounces of distilled water and 15 fluid ounces of acid, which may fill the tubes unless their diameter is above the usual average. | The panel of jin. ebonite measures 6; by 8% inches, and on it are placed the ‘sockets for tapping off voltages from each row of cells. If the con--structor desires other voltages in addition to those given, he can add the necessary sockets and tap the cells when required, but a strip of lead should always be soldered to the plate connector to stand upright, and the tap soldered to the top in the same way as done on gpe end plates. The sockets used will depend upon the pattern that can be purchased, but the style that siul flush with the panel makes the neatest job. Seven holes are drilled din. apart for the top row of sockets, ana ifin. from the top edge are spaced out tre holes for 0 and 112 socket, and the flex leads and fuse connections. Three-eighths of an inch above the bot.tom edge are the centres of the terminals carrying the three voltages, and the nevative and charging connections, and Zin. from the bottorn of panel .three holes are drilled to take fin. brass boits, fieads inside the panel, mad a washer and nut outside for the ends of the fuses. Under these bolts and the terminals is asmail plate of thin brass as 4 connector, and under the top end of which the fuse is clipped. Allow room at the sides for the thickness of tie wood supports and screw-holes to fix panel. Each piece of flex is abont six inches long, one end being connected to a pin to fit the sockets. The other end of the three voltage flexes goes behind the panel to the fuse bolt on its right The negative flex connects behind the panel to the negative terminal below it. The charging terin-_ inal at the right is merely connected to: the 112 socket as a convenience in con- | necting up the charger. When charg: ing up, all pins but the negative are plugged into the wood strip below the panel, and the charger is connected to the negative terminal, and the positive charsing terminal at the other end of panel. | The fuses are wade by pasting a siece of thin tinfoil upon a piece of writing paper, and then cutting this: into fine shreds with sharp scissors. ‘The best cuttings just over an inch long can be stuck with scccotine to a strip of strong paper, trimmed to size and the ends slipped under the washers and brass plate provided. These fuses may be considercd a difficult: thing to construct, but so long as there is a thin place in the length they will answer well, though very unevenly cnt, ainl will absolutely protect any valve from: damage by I.T. being "shorted". oyer the filament. | _ The acid should on no account be put into the tubes until the whole battery. is completed and ready for the plateforming. When all is ready, connect

up the charger, only the negative flex being plugged into the panel. urn on the current from the 2380-volt mains with a good resistance, one lamp at least, in series with the recitifier, Forming currents should be gentle, and nothing will be gained in any way by forcing the pace, In a few minutes the ositive plates wiil begin to show a colour if all is going well and the charging may proceed for an hour or so under supervision at frequent intervals. Then reverse the connections of the charger and leave for an equal time, so that the plates are reversed, those that should be negative now being brown. Then reverse again for double the time-now the positive plates will gain their proper colour, and in two hours reverse again, after which the charger may be connected the proper way and left for a few hours. The battery will not hold much current at first, but with continued charging cach day, and not being allowed to stand very long, capacity will soon come, and will increase rapidly with alternate charging and use. The rule that applies to other accumulators ap plies to this also-never to let it stand very long in a discharged state. Before commencing to form the plates if a chemical rectifier is to be used, make sure that the aluminium in it is pure, a thin strip of good metal will be far more efficient than a thick rod of doubtful quality, ‘There should only be a gentle glow round the aluminium, and if there is liberal sparking from it, rectification is not taking place, as thoroughly as should be desired. If there is any tendency for both negative and positive plates to turn whitish and a white deposit to be precipitated to the bottom of the tubes, charging should be stopped iminediately and nroper rectification obtained. However, if 2 reliable rectifier is being used, no trouble whatever is likely to be experienced. Use only enamelled wire, 22’s or 20’s for all wiring, and do not let the tap wires slope so that any Moisture on them will run to soldered joints or down to the panel. To charge this battery from 105-volt made or peocured, mounted on a small ebenite panel and fixed in a convenient position on the outside of the case. ‘The only actual alteration in the battery is to take ont the wire connecting 56-volt tap to 58 minus, the latter then being connected to the middle contact of switch. A wire is led from 56 tap (b) to the right-hand arm of switch; the left-hand is connected to O socket, and the right-hand contact of switch is connected to 112 socket. Theleft-hand contact of switch is a blank. When the switch is pushed to the right over tlie two contacts, the two halves of the battery are placed in parallel for charg. ing at 105-volts or thereabouts. When charging is completed the switch is pushed to the left, and so places the battery in full series for reception. With chemical rectifiers a lamp or suitable resistance must be included in the circuit, whatever the voltage of the Mlaisis, If it is decided to put paste into the plates, holes must be ptinched through them from what is to be the inside, and any excessive burr can be taken off with a sharp chisel. A two-inch nail will make a suitable punch. Instead a nn eee se of the plates being folded into a U. shape, they must be folded over a strip of 1-16th brass 3 wide and, say, 6in. long. Where the long edges meet they are to be turned towards each other on the edge of the brass by tapping, so that they meet fairly closely with the

brass strip inside. The strip can now be withdrawn at the end, and the two edges of the plate separated far enough to allow of the paste being put in, sufficient for a thickness of, about 1-16th of an inch. Now the two parts of the plate are pushed together again and the ends tapped down with a hammer to keep the paste in place, whilst the whole can be tapped down with a piece of wood laid on and struck with the hammer in order to consolidate the paste. ‘There must be no wide gaps at the joins or the paste will gradually d its way out. The constructor would probably get the paste from old accumulator plates as the readiest source of supply, and each pair of plates must have one filled with the positive and one with the negative paste, and eight end plates of each. ‘The celluloid separators, one for each cell, can be strips 6in. long and 4 or $ wide, bent by warming, to give the acid free contact with the surface of the plates. It would always be possible to convert the plain plates into pasted ones even after the battery had been in use for some time. It is just as well to note tliat all dimensions given should be taken as

approximate only, and that they may be modified as found necessary. Unless the tubes are very full in size, the plates should be cut 1} inches in width to give minimum trouble in fitting. The separators can be put into the plain plates before the latter are put into the tubes, each pair down one side of the row to have a separator near the top of each, and those on the other side to have a separator near the bottom of each. The main point in making the frame is to make all divisions an equal square that will take the largest of the tubes without any jamming or forcing. An easy way to arrange this is to mark on the edge of a piece of paper the width that will take the tubes and the thickness of the laths used.. Then take a piece of lath and mark off these dimensions the required number of times, remembering that no lath thickness is required at the ends, as all four sides are put on separately, nailed with thin brads. The cleaning of the lead is very important, whether pasting or not, and none of the cleaning material should be left on the surface. If the battery is intended for heavy! duty, pasting will be well worth the trouble, as it will give several times the capacity, and almost full capacity will he available at once, which is not the case with the plain plates. To make the paste, old accumulator plates are broken up, negative and positive kept separate; the hardened paste is then ground to a powder and made into a stiff paste by mixing with acid of the saine strength as used in the battery. The old plates used must he free from "sulphate," which is a whitish deposit that shows on the surface. Tor pasted plates more holes may be made in the lead than are shown in the diagram, and so long as the diameter is well under one-eighth inch they might com

veniently be made with a pair of punch-. ing pliers, afterwards hammering flat. Cut a trial pair of plates and test them for fitting in the tubes before cutting of the whole lot. This may save a deal of extra work at a later stage. When all the plates and separators are in place ready for the acid, test across each cell with a dry cell and ‘phones or galvanometer, which will show if any plates are touching and require separation. f lead weighing 3lb. to the square foot can be obtained, it will answer well, and in that case the total weight will be about 24lb. ;