Sunday, November 14, 2004

Lesson 14

ELECTRICITY LESSON 14 – Cells in Series and Parallel
Lesson: 14.
Take up Hwk: Discussion Questions text 307 #1-4
Quiz
Lesson: series and parallel circuits text pg. 310-311
Lab activity: build series and parallel circuits
Homework: pg. 311- 1-3



Board Note:

Cells and batteries may be connected in series, parallel, or combinations of both. Cells or batteries connected in series have the positive terminal of one cell or battery connected to the negative terminal of another cell or battery. This has the effect of increasing the overall voltage but the overall capacity remains the same. For example, the 12-V lead-acid automobile battery contains 6 cells connected in series with each cell having a potential difference of about 2 V. Another example of cells or batteries connected in series is shown in Figure 2. Cells or batteries connected in parallel have their like terminals connected together. The overall voltage remains the same but the capacity is increased. For example, if two 12-V automotive batteries were connected in parallel, the overall voltage for the batteries would still be 12 V. However, the connected batteries would have twice the capacity of a single 12-V battery. Another example of cells or batteries connected in parallel is shown in Figure 3.


Series and Parallel Cells Overhead

Portable equipment with high-energy needs is powered with battery packs in which two or more cell are connected in series. Figure 1 shows a battery pack with four 1.2-volt cells in series. The nominal voltage of the battery string is 4.8V.
Figure 1: Serial connection of four cells. Adding cells in a string increases the voltage but the current remains the same.



Parallel connectionTo obtain higher ampere-hour (Ah) ratings, two or more cells are connected in parallel. The alternative to parallel connection is using a larger cell. This option is not always available because of limited cell selection. In addition, bulky cell sizes do not lend themselves to build specialty battery shapes. Most chemistries allows parallel connection and lithium-ion is one of the best suited. Figure 3 illustrates four cells connected in parallel. The voltage of the pack remains at 1.2V but the current handling and runtime are increased four fold
Figure 3: Parallel connection of four cells. With parallel cells, the voltage stays the same but the current handling and runtime increases.



Here is a very good website for learning more on this topic:
http://www.batteryuniversity.com/partone-24.htm































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