Ques. What voltage should be used in charging?
Ans. At the beginning of the charge the voltage should be about 5 per cent. higher than the normal voltage of the battery, unless the latter has been overdischarged, in which case the difference of pressure should not exceed 2 per cent., otherwise the current might be too large.
Fig. 1,123.—Diagram showing charging connections for "Exide" duplex sparking battery. C, charging source; D, double pole single throw switch; E, single pole single throw switch; M, lamp resistance "main" battery; R, lamp resistance "reserve" battery.
Ques. In what two ways may batteries be charged?
Ans. They may be charged either at constant current or at constant voltage.
Although the latter method is considered the better one by many authorities, it is a fact, nevertheless, that if the charging current be normal at the beginning of the charge, and no means be provided for keeping it constant, it will diminish as the charging progresses, thereby greatly increasing the length of the time required for charging, and resulting in serious injury to the plates.
Ques. How may the charging current be kept constant?
Ans. Its voltage should be gradually increased, first to about 10 or 15 per cent. above the voltage of the battery, and kept at that point nearly to the end of the charge, where in consequence of the rapid rise of pressure in the battery it might become necessary to increase the voltage of the current to 30 or 40 per cent. above the normal of the battery.