CHARGING ACCUMULATORS WITH DANIELL CELLS

Radio Record, Volume I, Issue 20, 2 December 1927, Page 12

CHARGING ACCUMULATORS WITH DANIELL CELLS

ALTERNATIVE TYPE OF CELL DISPENSES WITH POROUS POT

ft has been proved by experjence ‘that the method of charging small aceumulators from_a trickle-charge supplied by Daniell cells is quite a practicable proposition for listeners in country districts. The mistake must mot be made of expecting such an out"fit to work without any supervision whatever, but it is clear that if a certain amount of supervision is civen, -and any wrong tendencies corrected, sthat good service may be obtained at ‘tow cost. Au Auckland reader writes to say that he was using this method successfully for over three years some time ago. He also sends a journal ‘containing a description of the form "of Daniell cell used by him for the purpose. In view of the difficulty already foreseen in procuring porous pots in New Zcaland, this form of cell is welcome. -Leclanche cells of sac type have been mentioned as being suitable for this work, but "Megohin’’ feels cer-

tain from past experience that ~ the Daniells will easily out-distance any Leclanche type for constant service. The gravity cell is not new to the writer, and the endorsement of its ,ase for the purpose by an Ifnglish _ publication is reassuring, ' THE GRAVITY DANIELL CELL. The container is a Sib. glass jam ar, or its equivalent, with a large open seck, and a strip of wood one ich nide to rest on top to support the plates. This would be improved by lipping in melted candle-wax. Two erminals are provided. The positive clectrode is a strip of hin copper shect about 10 by 23 inches, ‘oiled in the bottom of the jar in

the shape of a letter S. A strip one quarter-iucli wide is gut from one edge of this, leaving one end connected, and this strip is bent upwards to connect to the uut under terminal. This strip has to be effectively insulated to prevent direct action across the zinc, and this is effected. by slipping over it a piece of cither rubber or glass tube. So long as the upper end of this comes well above the surface of the liquid it will be right. By doubling the copper strip all the. way along to make it one-eighth wide, narrow rubber tubing can be nsed as an insulating sleeve. ‘The usual zitic is a cast block of semi-circular shape, about one inch thick. Zine is almost as easily melted as lead, and a handy person could possibly cast such a block from scraps, using a plaster mould. A thick strip of zine pushed in just before the metal sets would act as a hanger. If a copper wire is used for that purpose it must be well shellaced to insulate it. In case of difficulty in the way of casting, no doubt thick sheet zine could be suitably cut and bent to give the same effect. It should be noted that there must be a space of two inches between the hottom of the zinc aud the top edge of the copper. TILLING THE CELLS.

When the plates are im position the jars are to be half-filled with either a solution of sulphate of zinc or a weak solution of sulphuric acid (not more than one part acid to four of water). Next, about a pound of copper sulphate crystals is dropped in, when the liquid should just rise above the zinc; if not, a little more solution can he added. More copper sulphate has to be added every two or three weeks as required, but the solution need not be renewed for montlis. When the copper sulphate is added it will be necessary to first draw off a depth of an inch or two of the upper liquid by means of 18 inches of thin rubber (or glass) tube used as a syphon, The end of this syphon must draw off the top of the liquid only, and not be allowed to go near the copper sulphate lower down, After the new crystals are added, water is put in tu the usual height. CELLS TO BRE KEPT IN CIRCUIT. The cells should always be kept in circuit, as shown in the original diagram. If they are cut ont of cir- cuit the copper sulphate solution will tise above the zinc and cout it--with copper. In case of not using inuch current for a time, perhaps While away ou a holiday, the copper sulphate may be allowed to run down and, if not replenished, the cells may be cnt out of

the circuit for a fortnight, or even three weeks. Upon replenishing with copper sulphate, the cells will be back to normal in about a quarter of an hour. Users are recommended to pour a thin film of machine oil on the surface of the liquid, to prevent both "creeping" of the solution and evaporation. ‘Ihe same number of cells will be required for each voltage as already specified for the original type of ceil, It is an essential to the working of these cells that they should not be shaken about, so that they should be kept in an accessible place in a sttitable box to exclude dust, SMALL ACCUMULATORS ESSENTIAL. A cortespondent points out that these cells are not to be looked upon as being for charging run-down accumulators, bat only for replenishing what is taken out. Of course, this is meant to imply that large current is not available for charging accumualtors on any big scale. It as just as well for constructors to bear this is mind, aud remember that the device is really a ttickle-charger, working slowly, to replace during the night and the early part of ext day the even- ing’s consumption of current. Small acctunulators are specified, and_ it must be understood that anybody wishing to work with accumulators of large capacity will not find it very satisfactory to do so, and if they are determinced to try, must de so at their own risk. Small accumulators are the correct thing for any system of tricklecharging. The gravity cell has a very low inral resistatice of about half an olim.