Fig. 1,129.—Interior view Northwestern storage battery. The positive plate is of double grid construction, and the negative plate consists of a special staggered grid. The separators used between the plates are hard rubber, ribbed on one side so as to prevent the positive plate from buckling. It is perforated so as to allow a free circulation of the electrolyte and to decrease the internal resistance. Rubber separators are better than the commonly used wood or paper separators because they prevent local action. The flat side of each separator is placed against a positive plate, preventing shedding or jolting of the active material of the plate. This checks deterioration. The jars are made of rubber composition; the walls are thick and the covers well fitted to avoid spilling the electrolyte. All Northwestern batteries are contained in rubber composition jars. The walls are thick and the covers fit tightly to prevent spilling the acid. A hard wood box, treated with a moisture repellant is used for the outer case. These batteries are made in any voltage desired, the ampere capacity ranging from 25 amp. hrs. to 300 amp. hrs.
Ans. When a battery is being overhauled, the cells must be connected together in series and to the charging source in relatively the same manner as if they were in the vehicle; that is, the positive (+) terminal of one group of cells must be connected to the negative (-) terminal of the next group, and the two free terminals, one positive and the other negative, must be connected respectively to the positive and negative terminals of the charging circuit, but not until all of the groups have been connected in series. Great care must always be taken to have the polarities correct and the wire or cable for the connections of ample size to carry, without heating, the heaviest current used in charging.
Charging Small Cells.—For cells of the portable type, having capacities from 10 to 100 ampere hours, the normal charging and discharging rate should be about one-tenth the stated capacity, but the discharging rate may be increased to double this value, in case of necessity.
If the cells be provided with formed plates and not charged, the jars should be filled with the proper electrolyte, and then charged for at least 10 hours steady, or until they boil, then they may be discharged.
In the case of unformed plates, the charging should be from 30 to 40 hours, until the cells boil, and the plates assume their proper color.
Ques. How are small cells easily charged from 110 or 220 volt circuits?
Ans. This may be conveniently done by inserting in one of the charging leads an incandescent lamp which will pass the required quantity of current. If the current required be as large as 10 amperes, a suitable resistance or 10 lamps in parallel, each passing one ampere, may be used. Great care should be taken to see that the battery is connected properly.
Period of Charging a New Battery.—In the case of batteries provided with formed plates, the first charge should extend over a period of not less than 30 consecutive hours, without stopping, if possible, or for periods of not less than 10 hours a day for three consecutive days. The electrolyte will then commence to "boil" or "gas," assuming a milky appearance due to the ascending bubbles of gas. At this stage the density of the electrolyte as shown by the hydrometer placed in each cell should be at least 1.200; it is essential that the charging should be continued until every cell boils equally. From this point the charging should be prolonged until the pressure, as determined by a voltmeter or a cadmium tester, rises to about 2.55 volts.
