Chapter 7 Sources of Electricity 115 cell only. Although the voltage has not increased, the life of the battery has been increased because the current is drawn from all cells instead of just one. Th e amperage is added by connecting cells in parallel. Series-Parallel Connection Cells can also be connected in a mixed grouping. In Figure 7-14, two groups of batteries, each with a six-volt terminal voltage, are connected in parallel. Th e total voltage is still six volts. But the capacity has been increased by this series-parallel method of connecting cells. Th e total current is added, giving two amperes. 7.1.5 Battery Capacity It is important that you understand the term capacity as it relates to batteries. Th e capacity of a battery is its ability to produce a current over a certain period of time. It is equal to the product of the amperes supplied by the battery and the time. Capacity is measured in ampere-hours (Ah). Th e description of an automotive battery might indicate a capacity of 100 ampere-hours. Th is would mean that the battery could supply: 100 amps for 1 hour 100 × 1 = 100 Ah 50 amps for 2 hours 50 × 2 = 100 Ah 10 amps for 10 hours 10 × 10 = 100 Ah 1 amp for 100 hours 1 × 100 = 100 Ah A battery will not perform exactly by this schedule, as the battery’s rate of discharge must always be considered. A rapidly discharged battery will not give its maximum ampere-hour rating. A slowly discharged battery may exceed its rated capacity. Th e Society of Automotive Engineers (SAE) has set standards for the rating of automotive batteries. A manufacturer must meet these standards in order to advertise a battery as a specifi c ampere-hour capacity. Several factors determine the capacity of a storage battery: ■ Th e number of plates in each cell. An increased number of plates provides more square inches of surface area for chemical action. Automotive batteries are commonly made with 13, 15, and 17 plates per cell. Th e number of plates is a determination of the life and quality of a battery. ■ Th e kind of separators used has an eff ect on the capacity and life of a battery. ■ Th e general condition of the battery with respect to its state of charge, age, and care will infl uence the capacity rating of any given battery. To compare primary and secondary cells and batteries, refer to Figure 7-15. Note that their most common uses are given. Flashlight Cells + – + – + – + – + – 1.5 V @ 1A 1.5 V @ 1A 1.5 V @ 1A 1.5 V @ 1A Schematic Symbols 1.5 Volts 4 Amperes Goodheart-Willcox Publisher Figure 7-13. Pictorial and schematic diagram of four cells connected in parallel. This connection only provides 1.5 volts, but with 4 amps of current. 1.5 V @ 1A 1.5 V @ 1A 1.5 V @ 1A 1.5 V @ 1A 1.5 V @ 1A 1.5 V @ 1A 1.5 V @ 1A 1.5 V @ 1A 6 Volts 2 Amperes Flashlight Cells + – + – + – + – + – + – + – + – 6 Volts 2 Amperes Schematic Symbols Goodheart-Willcox Publisher Figure 7-14. Pictorial and schematic diagram of two groups of cells connected in series and those two groups connected in parallel. Copyright Goodheart-Willcox Co., Inc.