Frederick A. Draper.

A very common desire of amateurs interested in electricity is that of a small lighting outfit, with accumulators or storage battery as the source of current. Many have hesitated to attempt setting up such an outfit, being deterred from so doing by the supposed difficulties of charging the battery, as they do not have recourse to a charging dynamo or lighting circuit. Where the above condition exists a charging battery composed of "gravity" or other cells, can be used, the chief objection being the long time required for charging. As the demand on the storage battery is generally but a few hours at a time, the charging battery has the remainder of the time for keeping the storage battery fully charged, so the matter of time is not as important here as it otherwise might be.

The outfit to be described contemplates the use of 10-volt, 6 C. P. lamps fitted with full size base, thus allowing standard plugs, sockets and fixtures to be used, which may be purchased at less cost than those known as "miniature. " This voltage will require five cells of storage battery, and as a serviceable and easily made type was described in the June, 1904, number of this magazine, readers are referred to that article for directions for that part of the work. The making of a "gravity " battery was also described in the November, 1901, number, and as quite a number of cells are required, they can be made at a considerable saving if materials can be readily and cheaply procured ; otherwise it would be best to purchase them complete.

The storage battery mentioned is of 15 ampere hours capacity ; that is, it will furnish a continuous Current of one ampere for 15 hours, two amperes for half that time, etc. As the lamps mentioned above require from .7 to .9 ampere each, we can easily calculate the number of lamps and the length of time for which the battery will supply current. Neglecting the resistence of the circuit, which would be small, it would be well to allow one ampere per lamp per hour, and as too fast a discharge rate is injurious for the battery, four lamps is about the largest number that can be used at a time, as nearly four hours could be obtained from each charging. As the charging battery is constantly at work the service mentioned can easily be obtained. By using lamps of less voltage and candle power, fewer cells in both storage and charging battery would be required. For lamps of 6 volts and 3 C. P., only three cells for the storage battery would be necessary.

In calculating the number of " gravity" or charging cells required, it is necessary to first determine the discharge rate of the storage battery. If the latter is to be used to about its full capacity each evening, the charging battery must have a greater number of cells than would be the case if only half the capacity was used each evening or the full capacity every other evening, and it may be well to state that if fitted up for the service last mentioned it is perfectly feasible to have service in either of the two ways. If the storage battery is used one evening to its full capacity, double the time is required for charging with the smaller battery as with the larger. With this explanation we can now determine the number of cells needed for the charging battery.

The discharge rate of a single "gravity " cell is about .5 amperes, at a trifle under one volt. The charging current should be about 2.5 volts per cell, making the voltage of the charging current 12.5 volts; which is what is obtained from 14 "gravity" cells when connected in series. At the rate of .5 ampere, 30 hours would be required to charge the storage battery; double the number of "gravity " cells connected in series-parallel; that is, two sets of 12 each in series connected in parallel, would do it in 15 hours. The reason is plain, therefore, why such a large number of charging cells are required.

Wiring Diagram

The battery described in the July, 1903, number of this magazine should work well as a charging battery, although the writer has had no personal experience with its use in this way, and has been able to obtain a discharge rate of a trifle less than 1.5 amperes, but even at this rate only 10 cells would be required to charge the storage battery to its full capacity for daily use. Those making up all the outfit are recommended to give this type of cell a trial, as the cost is very little

Having completed our batteries, the next thing to require attention is the assembling and wiring together with the necessary switches, etc. A volt and am-meter of suitable capacity would add much of interest in the operation of the outfit, and as well-made instruments of the required capacity can be obtained at little expense, they should certainly be included. The batteries should be placed in a suitable cupboard, the interior having first been painted with asphaltum paint, making it acid-proof. Two large shoe packing cases fitted with shelves will answer the purpose excellently. The wiring and several connections are clearly shown in the accompanying diagram. It will be noted that the lamps are connected in parallel. Ordinary annunciator wire, No. 16 gauge, will answer for wiring if not over four lamps are connected, the wires being separated an inch or more and wrapped with electricians' tape, where tacked to supports or, better, carried on small insulating knobs. Sold erall joints, as twisted joints are apt to corode and cause unnecessary resistance.

Having assembled the batteries and completed the wiring, the electrolyte poured in, charging should be started at once and continued without interruption until the plates are formed. About two days will be required for the first charging, a less time with each subsequent charging, until the normal working condition is reached. At first the positive plates will quickly become a dark brown color, changing to a lighter color, and then gradually darkening to a deep brown. The negative plates will, at the same time, turn to a dark grey and are then fully charged. They should be immediately discharged by means of the lamps, not by short circuiting, and then charged again. If time will permit before the second charging, it is of considerable benefit to the life of the plates if they are taken out, thoughly washed in water and allowed to dry for a couple of days before again being placed in the electrolyte.