An Efficient "B" Battery Accumulator

Radio Record, Volume I, Issue 39, 13 April 1928, Page 12

An Efficient "B" Battery Accumulator

Charges at Low Vo

By

MEGOHM

ERE ts tis promised B acgumulator, so arranged that it can be charged up quickly and reliably with the A battery charger dewhet) sctibed on March 2. The chief departure from the orthodox arrangement is that the test-tubes ate arranged iti rows, seven in each row, or a total of fourteen volts in each row. The end plate of each row is connected to a.length of wire sufficient to reach across the top of the battery and join up with a similar wire from the opposite end of the next row. The joining is accomplished quickly and eflectively by means of a battery-clip attached to the end of each flexible wire. When the battery is used for reception the clips attached to the positive ends of the rows are all connected to the negative end of the adjacent row, then putting the whole battery in series. When charging is requited the clips are all taken apart and all positive ones clipped on the upper edge of a brass or lead plate on the front of the battery, in which a_ terminal is inserted for connection to the positive terminal of the charger. All negatives are similarly connected to a plate at the back of the battery, with a terminal for connection to the negative of charger. Thus the rows are all connected in parallel, or form a 14-volt battery of much iticreased capacity, and can be charged with a charger giving 16 to 20 volts. A strip of wood above the centre of the battery forms a support for the clips out of the way of the acid, and whilst charging is in operation the clips and connections are ‘more out of the way, as they are ontside the battery "case. It is left for the constructor to decide just what voltage he requires, but rows of six or seven tubes in each should be adopted, and the number of rows constructed to give the near--est voltage, which will be 84, 98, 112, or 126 volts. Wight rows, giving 112 volts, is a useful size, 56 tubes being required. . ‘he plates to be described will go into inch test-tubes, but ~if l-inch test-tubes are used there will he more room for liquid, which will not evaporate so quickly, and_ will not reanire distilled water adding so often. THE LEAD PLATES. TPUE lead plates, which will be afterwards pasted, are cut from strips of ridging lead used by plumbers, This lead is in strips 14 inches wide and 8 fect long, and as it is machine-planed from thicker strips, it is bright and clean, ready for use. ‘These strips are te; be cut into 12-inch lengths, one tor every tube to be used. ‘The diagram _shows how each plate is to be eut, and - _-- {

tlie best way to mark these for uni-/ formity is to cut a cardboard template and lay it on each in turn, scratching round the position of the cut-out portion in the centre. A point to be noted is that the portion shown shaded is to be cut out as waste, and the outer strip left joined at X, afterwatds to stand up clear of the acid spray, and to which the wander-clips may be attached for voltage tappings. "Phe plates for the end positions in the rows are to be separated by cutting the central connector at the end near X. ‘This will leave the two halves separate with a tag on each. It is not feasible to cut the narrow tag much wider, because it would then interfere with the bending of the plates. Tags for taps will not be necessary on very many of the cells, as the ends provide convenient taps. The first two ends give 14 and 28 volts, a tap in the centre of the second row will give 22, and in the centre of other rows, 36,. 50, 64, 78, 92, and so on, so that only about six need be cut with tags besides those for the ends. The total length of the plates when pasted end folded up will be 117 inches, as 4 inch at each end is folded over. A number of holes not exceeding paste, with dilute sulphuric acid of punched in the plates with an inch nail or other convenient point. These holes should consist of a row of about 8 or 10 down the centre and the same number just outside each dotted line. he more holes the better, within rea‘gon. If it is desired to take the burr off the holes, it may be done with a sharp chisel, but the burr may be on what is to be the inside of the plates.

BENDING THE PLATES. BENDING is the next operation. The plates have first to be bent at the dotted lines running the full length, forming a kind of gutter shape half an inch wide inside, or the purpose, a strip of wood a half-inch thick is prepared, and the two corners slightly rounded off. This wood_ is then placed over the lead and the sides are bent up as shown in section. MAKING THE PASTE. THE plates are now ready to be filled with paste, one end of each plate being filled with positive and the other end with negative paste. The negative paste is made from litharge, | a buff-coloured powder, and the positive is made from ordinary red lead. These are not expensive, and the amount required will vary with the number of plates and the amount of paste put into them. Abont 1} to 2lb. of each should be ample. A quantity of powder is taken and mixed on a sheet of glass to a stiff paste, with dilute sulpkr.re acid of usual battery strength, usine a wooden spatula, which may be made from a strip of wood thinned down. When a quantity of one of the pastes has heen mixed, it can be laid in one end of each plate to a depth of one-eighth of an inch. The lead on each side is then folded down to overlap, and the quarter-inch at the bottom ends is turned up and all corners and joints attended to and pressed together to be as close as possible. The top ends also must be closed up, and to facilitate closing, the paste slould not be laid too near the ends. The other ends may next be treated with the opposite kind of paste and closed up. All the plates are now to he laid aside to drv for several days, or a week, if possible, as thorough drying helps the paste to stay in the plates, though the form of construction gives it little chance to get out. Care should he taken to make the end with the tags either all positive or all negative, to preserve uniformity for tapping THE BATTERY CASE. RxAct dimensions will be left to the constructor, as they will vary with the number and diameter of tubes decided upon. One item that should he adhered to is the division between the tubes, which should be #-inch wood. There are several ways of supporting the tubes. One method is to bore holes in a sheet of three-ply or }-inch wood, and in the base drill countersunk marks

to take the lower end of the tube. Another way of supporting the top end is by dropping } laths in between each row, a set of isths running each way, cne set resting on those below, and the lower ones resting on strips inside the two ends of the case. ‘The laths need not be fastened, as the tubes keep them in place. As much as possible of the front and back of the case should be left open to give a good view of the plates. The strip of wood over the top to ‘support the clips should not be less than 4in. above the tops of the tubes, and could be 1} to 2 inches wide. ‘The tubes should project nearly an inch above the strips that support them. Test tubes are very irregular in size, and "inch" tubes will vary in‘ inside measurement from + to }-inch. Messurements must be inade to allow for the largest sizes being accommodated.

BEFORE the tubes are put into place the tops shoula be smeared with vaseline with the finger for a depth of half-an-inch both inside and outside. All portions of the plates above the acid level to within abcut half-eh-inch of the topend of tags and over all cell-to-cell connectors. * If there are any soldered joints on tags it pays ‘to coat them with celluloid cement or shellac and then liberally apply vascline. In time the acid eats through un»rotected copper wire. On no account neglect the vaseline. GENERAL. (PoE connecting wires should be flexible wire with rubbcr covering only-any kind of fabric soon rots with acid spray. An alternative way is to double in half two lengths of 26’5 enainelled, clean the enamel off the loop end and fasten to the screw of the battery clips, and solder loose ends to tag of plate. Another method is to waste a small amount of lead by cutting separate end plates with a tag ofssufficient length and attach the clip to the end, Considering that the battery will only need charging about once every two weeks, when Well formed, there will not be much wear on the connectors.

Have the negative end of every row at the front and the positions at the back, or vice yersa. The two ends, negative and positive, can be permanently joined by a soldered wire to the front and back plates respectively. ‘The terminals will then he the negative and power-valve connections to the set when charging is finished. If preferred, a 1-16 drill could be used to make holes in the plates, as several could be drilled together, When not charging, a coarse cloth can be thrown over the top of the fattery to exclude dust, or otherwise a deep wooden lid could be anade to dropever the top. The plates are kept from touching in the tubes by a strip of motor-hood celluloid or glass, about 64in, long and a very easy fit for the width of the tube | used,

THE ACID SOLUTION, ie pays to use good acid in a small accumulator such as this, so pure sulphuric acid should be purchased, Five parts of acid to twenty-one of distilled water is the correct strength to use. Place the water in a basin and add the acid gradually, stirting with a glass rod or other acid-proof article, Considerable heat is generated during the process of mixing. If distiJled water is diflicult to procure, water that has been boiled and allowed to cool is a good substitute. Where there is choice, rain water is better than artesian, ag the latter often contains traces of 1iineral salts. When calculating the amount of liquid wequired for the tubes it must be remembered that it 7s only necessary to provide sufficient to properly fill half the number of tubes without plates in, because the other half is necupied by the plates. The plates must all be in position and all construction work finished when the acid is put in, and‘ then . the first charge may be proceeded with. THE: FORMING CHARGES. With the end-of every row connected to the nearest plate, the two terminals are connected to _ the charges, positive of battery to positive of charger, and negative to negative. A length of, say, five or six inches of 36's nichrome resistancé wire or ‘other kind of resistance should be inserted in the positive lead to ensure only a gentle current from the charger, but notice should be taken that minute bubbles soon begin to comie away from the plates, showing that charging is proceeding. The resistance should never be sufficient to lower the voltage below the necessary amount. Af-

ter 10 or 12 hours the wattery may be disconnected from the charger, connected up in series, and discharged through an electric bulb, 230 or 110 volts, fixed in a socket with wires to attach to the battery terminals. This lamp should be, left connected until it dies out, which will not be for several minutes, which should be carefully timed, as comparison will indicate the increased capacity with later charges. After this first charge, charge up again for, say, six hours, when, if anxious to test the battery, nse it on the set for a session, but immediately afterwards discharge with the lamp and put on, charge again for a further six hours. Altogether it is as well to give a total of 36 to 48 hours’ initial charging, but care must- be taken to keep the charging rate down with the resistance, which may be reduced a little after the third charge. The amount of resistance to be permanently used will depend upon the number of rows of cells. The total cost of the battery should be well under £2 for the 112-volt size. One-inch test-tubes cost about 18s. for the half-gross, and three-quatters a little less.

| When the first charge has heen 0 | progress for half an hour, the owside of the plates should begin to show the respective colours, deep chocolate the positive and grey for the negative. At a later stage the positive plates will be inclined to show a lighter brown in colour, but will later assume the deep tone and_ retain it. The object of the initial charges is chiefly to turn the red lead into the correct positive compound. During the early life of the battery it will be as well to charge at Icast once a week, and after a few weeks the time of recharging may be extended. During this time keep an eye on the positives, and if they turn light in colour it may Le an indication that the battery has been standing too lone and requires a charze.

Do not attempt to increase the thickness of the paste over }in., wiich will give plenty of capacity. Plates must be at least half an inch above the bottom tubes to allow room for possible sediment. The liquid is to be kept a quarter of an inch above the tops of the plates, which are jin. below top of tubes Those who have not had much to _do with accumulators may be inclined to leave short tags for taps, but it is important to have them as long as possible clear of the spray and acid, as the latter creeps up gradually and causes dirty contact for tie clips. This battery can be charged with any charger giving 16 volts or more. Tf you have a charger giving only about 14 volts, put only six cells in a row. Every cell gives two volts. The plates ‘at back and front are made to stand ont by mounting on a strip of wood. Clips may then be attached to either the upper or the lower edge.

PHILIPS LABORATORIES AN advance copy of a.folder from the Philips Laboratories announces several new items, of which samples first appeared in Australa at the recent Sydney Radio and Electrical Exhibition. There is an audio transformer giving even amplification from 200 to 10,000 cycles, ratio 3-1, and it is claimed that if preceded by the 415 valve that the average "step-up" is 45 per stage. Splendid results are also obtained with A409 and A609. mS New Power-Valves. Two new 4-volt power-valves are announced, the B409 and B405. These are economical of plate current, and work on low grid bias. The B voltage recommended is 150. B ari C Eliminator. " The "Power-plus: B and C Elimirator gives grid-bias at three d‘fferent voltages up to 40 volts maximum. This is suited to ordinary receiving sets or those using A.C. valves. New A.C. Valves.. Three types of alternating-cur-rent valve are announced. C142 for R.F. amplification with a factor of 150, is a screen-grid type using’ a.c. directly on the filament. The F215 is a special detector, therefore indirectly heated, and has_an amplification of 15. The D143 is a power-tube with an amplification of 150 and contains three grids, the filament being heated directly with

a.C. Low Capacity R.F. Valves. Interesting news is the production of two special valves for R.F. amplification, dispensing with the usual neutralising devices, yet giving exceedingly high amplification of RF, signals. When used in cascade (several stages) they can be stabilised by very simple devices on account of the internal capacity being reduced to about 60 per cent. of that in the average valve. The A635 is a six-volt valve taking .06 amp., with amplification factor 35 and impedance 23,000 ohms. The A435 is a four-volt valye taking .06 amp. with an amplification factor ef 85 and impedance 29,000 ohms. The popular 18/6 is to be the price of these special valves. "A"? Trickle Charger. A trickle-charger for the ‘‘A" battery is also announced, which can be made to give an output varying from .01 to .17 ampere, the latter sufficient to keep an "A" battery operating the largest of teceivers always at peak. New Loudspeakers. A new loudspeaker of the cone type is a slightly smaller replica of the popular ‘"PCJJ"’ type, and sells at a lower price. Full volume is reproduced without rattle or distortion. It is to be known as the PCI Junior." A smaller and less expensive type still, incorporating the same balanced magnet and floating cone system is the "Baby Grand." (Continned on Page 18.)

Construction | Continued —

DEVELOPMENT OF THE DETECTO St ee Vy ERE it not for the valve, wireless telephony, as we know it, would neyer have been born, Though attempts were made in the early days to employ an "Are System,"’ the valve is necessary in all the present-day practical systems of transmission. And owing to its amplifying effect, the valve becomes an almost indispetisible ad--junct for the comparatively distant lis--tener who desires to hear the transmissions on what are really the very low powers used in ordinary broadcasting. The advent of high-powered broadcasting stations has, of course, opened the eyes of the ‘man in the street’’ to the fact that the "range" of a crystal set depends on the power of the transmission, and not on any inherent "range of reception’? of the receiver. Before that the writer met several crys-_ tal users who were under the impres. sion that ‘a crystal couldn‘t receive farther than 15 miles."’ ‘Ihe fact that signalling was for years carried on commnietcially over very long distances by. the use of receivers much less sen-| sitive than the crystal, and without the aid of any amplifiers whatever, was mews to them. It is, of course, the amplifying property of the valve and not any great superiority purely as a detector that enables us to receive weaker signals, even with a single-valve set, than we ean with a crystal. Rud the original valve was in existence a loug time hefore it could compete successfully with the other methods of detection. What: really brought the valve to the fore was the discovery of reaction, which is essentially nothing more than ‘2 means of providing H.F. amplification ly means of the detecting valve itself, ii addition to the L.F. amplification inherent in the 3-electrode, though not in the originel Fleming 2-electrode detecting valve. Visible Detection. BEFORE the discovery of reaction the valve, even the 3-electrode valve, was comparatively ‘small potatoes." In the 1911 edition of the "Admiralty Manual of Wireless ‘Telegraphy,’’? a hook of some 370 pages, the whole subject of valves, which had been in existence some time, even, in the case of the Fleming valve, a long time, is dismissed in a single pagel ‘The ‘Audion,’ as the 3-electrode valve is there called, is condemned because of the necessity (reaction being unknown) of burning the filament so brightly, to obtain the maximum sensitivity, that the life. of the valve is very short, and the valve detector, therefore, toe expensive for general aloption! What, then, were the detectors that had been used up to that time, and with which, unaided by amplification, signals were received over hundreds of miles, even across the Atlantic ? Historically, the first method employed was the observation of the minute sparks jumping the gap in a nearly elosed circuit. Since the pressure produced in an aerial by even the most powerful signals is exceedingly small, it will be understood that this gap, across which the pressure had to force the sparks, was necessarily very marrow. So nearly had the ends to he joined that the use of a microscope was tried to watch for the sparks! This, the original detector, was naturally very insensistive and not very practical, The Coherer. A GREAT sfride was made with the " introduction of the ‘‘coherer,’’ the first standard detector used in the Navy. There were a number of such devices, the best known being that invented by Marconi, . This consisted of a glass tube exhausted of air, and containing a small pinch of nickel and silver filings between two silver plugs. The loose fil-

umemeed \ ‘ings offered a fairly high resistance to the passage of a direct current, but had the property of "cohering," or sticking together, when an oscillating current was applied. The resistance then fell, and the current from a small local battery was enabled to pass. This current was used to operate a machine, known as the ‘inker," which recorded the signals on a tape, in the same way as the familiar "tape machine." There were two grave disadvantages to this method. Firstly, the coherer required to he "tapped," by a_ special mechanical device, to shake the filings apart after each ‘‘long’’ or "short" had been recorded, and, secondly, the itker recorded atmospherics and other interferences as well as signals. Sir Oliver Lodge produced a coherer which did not require to be tapped, but the whole system was rendered obsolete by the invention, by Marconi, of the ‘magnetic detector." Marconi’s Maguetic Detector. THIS was a very ingenious device, depending on the fact that iron, when magnetised or de-magnetised by passage through a permanent magnetic field, does not either take up or part with its magnetism immediately.

ENNUDRAIOOOUR TOD ENSUES Several other types were introduced, but the magnetic detector held its own against them for a considerable time. The Electrolytic Detector. "THE electrolytic methodis one which | even now retains considerable in-| terest. ‘The principle is that a very. fine wire, preferably tipped with plat--inum, is adjusted so as just to touch the surface of a.small quantity of acid in a lead cup. This adjustment can bemade in a very similar way to the ordinary cat’s-whisker adjustment of a crystal detector. A small battery and a. pair of ’phones are connected with this arrangeirent, the whole circuit being exactly similar to that of a carborundum crystal detector, except that the detector and *phones are in parallel, The potentiometer is used to adjust the detector, the process being rather delicate, and there being no space to describe it in detail here. When adjusted, the effect of the current from the battery is to cause a tiny bubble of oxygen to form on the platinum point of the cat’s-whisker. ‘This bubble (being an insulator) stops the further flow of current. ‘The arrival of signals upsets the equilibrium of the arrangement, knocking the bubble off the cat’s-whisker, so that the battery sends a momentary current through the *phones, and the signal is heard, Directly the oscillations cease, the bubble of course re-forms, and the detector resets itself. This detector is very sensitive, but for obvious reasons it did not lend itself very readily to employment at sea. But it is still well worth the "erystal’? experimenter’s notice. The discovery of the "unilateral conductivity" of certain substances brouglit in the crystal detector, which is too well known to need description.