The following table gives the variation of capacity for different rates of discharge:
Capacity Variation for Different Discharge Rates
+——————————-+——————————————————————+ | Discharge | Per cent of capacity | | rate | at 8 hour rate | +——————————-+——————————————————————+ | | =Plante= | =Faure= | | 8 hour | 100% | 100% | | 6 hour | 96% | 96% | | 4 hour | 80% | 88% | | 2 hour | 61% | 70% | | 1 hour | 56% | 48% | +——————————-+——————————+——————————-+
[Illustration: FIG. 1,136.—"Exide" connector puller for removing connectors.]
=Ques. How may the capacity of a battery be increased?=
Ans. By mixing organic materials with the lead oxide, _but any such mixture is always accompanied by a rapid deterioration of the plates_.
=Discharging.=—In discharging a battery its voltage should never be allowed to fall below 1.8 volts, under load, thus leaving about 30 per cent. of the total capacity unused. The normal discharging current may be equal to the normal charging current, but a discharge equal to 3 or 4 times the normal may be given without injury to the plates. Some types may be discharged at even six or seven times the normal rate. In such cases, however, the capacity will be reduced in the same proportion, as before explained in the paragraph dealing with battery capacities.
[Illustration: FIGS. 1,137 to 1,151.—Parts of the Witherbee battery. 1, jar; 2, inside cover; 3, cover; 4, handle; 5, vent cap; 6, cover, screws, nuts and washers; 7, handle eyes, nuts and washers; 8, rubber covered nut; 9, spannernut; 10, plate strap for positive plates; 11, plate strap for negative plates; 12, rubber separator; 13, wood separator; 14, positive group of plates; 15, negative group of plates; 16, positive plate; 17, negative plate; 18, cell connector. An element consists of a complete set of plates bound together on strap, with wood and rubber separators for a single cell. Positive plates are brown, negative plates, gray.]
=Ques. What is the effect of discharging too rapidly?=
Ans. It tends to break the plates, and in the case of pasted plates, a very sudden discharge will dislodge the paste.
=Ques. How is the discharge capacity of a storage battery stated?=
Ans. In ampere hours. This, unless otherwise specified, refers to its output of current at the eight hour rate. Most manufacturers of automobile batteries specify only the amperage of the discharge at three and four hours. Thus, at the eight hour rate, a cell which will discharge at ten amperes for eight hours is said to have a capacity of eighty ampere hours. It does not follow that eighty amperes would be secured if the cell were discharged in one hour. It is safe to say that not more than forty amperes would be the result with this rapid discharge.