Fig. 1,130.—The Willard underslung battery box for automobiles. The general tendency in automobile design, is to keep everything off the running board as far as possible, and to get tool boxes, battery boxes, etc., placed somewhere under cover. To meet these conditions the box here illustrated is arranged so that it can be underslung beneath the rear footboard or supported on auxiliary cross members made of strap iron and attached to the side members of the chassis. It is usually suspended under the rear footboard or the rear seat. The box has a chemically treated wood lining to make it acid proof. The lining is so made that there is air space between the battery and the sides of the box, except at the corners. Ventilation is thus obtained and the battery kept dry. Accumulation of water or spilled electrolyte in the bottom of the box is prevented by grooves in the bottom board, extending downward from the corners to an outlet at the center of the board. The box is also fitted with rubber bushings in the holes where wire leaves the battery box.
The charging of unformed plates is similar in all respects to that of formed plates, except that the first charging should extend over a period of at least 70 consecutive hours without stopping, at the end of which time the plates should have the characteristic colors of those of a fully charged battery. If they do not, the charging should be prolonged and the cell tested for density of electrolyte, and voltage, as already described until the desired conditions are attained. Then the battery may be discharged and recharged.
It is probable that a total of 300 to 400 hours of charging with intervening discharges will be required to form the plates until they acquire a good color, and the density of the electrolyte becomes stable.
In regular charging, the rate should be rapid when the battery is nearly exhausted, but it should be greatly reduced at the end of the charge after passing the point of boiling. Charging at too low a rate is always injurious.
Ques. What may be said with respect to the capacity of a new battery?
Ans. A new battery will never give its full capacity till after about twenty discharges. During this time it should be given about 25% overcharge. After that, 10% overcharge, that is, 10% more charge than was taken out, will be sufficient for ordinary work.
High Charging Rates.—Occasionally it is desirable to charge a battery as quickly as possible. As a general rule, such a procedure should not be adopted unless the battery be thoroughly discharged, and not then, unless done by a person who thoroughly understands what he is about; battery makers will always furnish data and directions to meet emergencies.
In charging a battery at a high rate, the danger to be avoided is the tendency of the cells to heat. The troubles that might arise from this cause may be prevented by immediately reducing the current strength. The proper rate of charge for a given battery of cells may be thus discovered by experiment. A battery should never be charged at a high rate unless it be completely exhausted, since it is a fact that the rate of charge that it will absorb is dependent upon the amount of energy already absorbed.
Fig. 1,131.—Instructions for taking voltage readings ("National" batteries). The batteries are made up of several cells, usually two or three, each cell representing approximately 2 volts when battery is on "open circuit" (neither charging nor discharging). It is sometimes advisable to take individual readings of the cells, both to determine on charge if all the cells be evenly charged, and also on discharge to be sure that the cells are evenly discharged. To do this, a low-reading voltmeter must be used with prods attached to the voltmeter leads that can be forced into the terminals so as to insure good contacts. To test the positive end cell, put the positive prod on the positive terminal of the battery and the negative prod into small hole back of positive terminal in hard rubber cover. Middle cell (in 6 volt, type "Y" batteries) is tested by inserting the positive prod in the small hole back of the positive terminal, and the negative prod in small hole back of negative terminal. In the 120 ampere hour, Auto type of battery, the middle cell is tested by inserting the positive prod in the small hole back of the positive terminal and the negative prod on the middle terminal. The negative end cell is tested by putting the negative prod on the negative terminal and the positive in the small hole in rubber cover back of the negative terminal. A charging cell at end of charge should read about 2.55 volts. A fully charged cell on open circuit should read about 2.1 volts. Since open circuit readings vary under different conditions, as to age, acid, etc., little significance should be attached to them. A discharged cell voltage will vary considerably with the many different coils, engines, etc., but in the majority of cases should read between 1.8 to 1.9 volts, while motor is in operation.