Unit 13 Batteries and Other Electrical Sources

Transcription

1 Batteries and Other Electrical Sources

2 Objectives: Discuss the differences between primary and secondary cells. List voltages for different types of cells. Discuss different types of primary cells. Construct a cell from simple materials. Discuss different types of secondary cells.

3 Objectives: Connect batteries in series and parallel to obtain desired voltage and ampere-hour ratings. Discuss the operation of solar cells. Connect solar cells in series or parallel to produce the desired output voltage and current capacity.

4 Objectives: Discuss the operation of thermocouples. Discuss the piezoelectric effect.

5 Battery History Luigi Galvani in 1791 first noticed indications of electricity while experimenting with frog legs. Alessandro Volta in 1800 created the first practical battery. Batteries are composed of one or more cells.

6 Typical cell and battery schematic symbols.

7 Simple potato voltaic cell.

8 Simple nickel/paper/penny voltaic cell.

9 Voltaic Cells The individual cell voltage is determined by the construction materials. The electromotive series of metals ranks how easily they give up electrons. A primary cell cannot be recharged. A secondary cell can be recharged.

10 Electromotive series of metals list.

11 Voltaic Cells The amount of current a cell can deliver is determined by the surface area of its plates. The current capacity is the amount of power a cell can deliver. Primary cells are rated in milliampere hours.

12 Voltaic cells.

13 Carbon-zinc cell.

14 Mercury button cell.

15 Nickel-Metal Hydride Cells (Ni-MH) This type of cell is similar to nickelcadmium cells. Both types of cells have 1.2 volts per cell. Both types of cells have similar charge/discharge curves.

16 Nickel-Metal Hydride Cells (Ni-MH) Nickel-metal hydride cells have 40% higher energy density. Ni-MH cells are more environmentally friendly. Ni-MH cells are replacing nickel-cadmium cells.

17 Lithium-Ion Cells Lithium-ion cells can be recharged and have a very high energy density for their size and weight. The weight energy density is three times greater than nickel-cadmium cells. They have a voltage of 3.6 volts per cell.

18 Power comparison based on size.

19 Power comparison based on type.

20 Batteries Batteries have internal resistance that affects their performance. Series-connected batteries add their voltages while their current remains constant. Parallel-connected batteries add their currents while their voltage remains constant. Never parallel connect batteries of different voltages.

21 Series-connected batteries.

22 Parallel-connected batteries.

23 Combination-connected batteries.

24 Solar Cells Solar cells use the principle of photon energy striking a semiconductor material to produce electricity. Silicon solar cells produce an open circuit voltage of.5 volts in direct sunlight.

25 Solar cell schematic symbol.

26 Photovoltaic circuit.

27 Thermocouples A thermocouple is a junction of two dissimilar metals that produce a voltage when heated. A thermopile is a series-connected assembly of thermocouples used to increase voltage output.

28 Thermocouple.

29 Thermopile.

30 A safety system using a thermocouple.

31 Piezoelectricity Piezo is derived from the Greek word for pressure. Piezoelectricity is produced by some materials when placed under pressure. The pressure can be caused by compression, twisting, bending, or stretching.

32 Piezoelectric effect.

33 Practical Application 1 Your job is to order and connect lead-acid cells used to supply a UPS (Uninterruptible Power Supply). The battery output voltage must be 126 volts and have a current capacity of not less than 250 ampere-hours. Each cell has a rating of 2 volts and 100 ampere-hours. How many cells are required?

34 Practical Application 2 Your job is to replace a bank of nicad cells used to supply emergency lighting with a bank of lead-acid cells. There are 100 cells in the original nicad bank. Each cell has a 120 ampere-hour rating. The lead-acid cells each have a 60 amperehour rating. How many cells are required?

35 Review: 1. The first practical battery was invented by Alessandro Volta in A voltaic cell converts chemical energy into electrical energy. 3. A battery is a group of cells connected together. 4. Primary cells cannot be recharged. 5. Secondary cells can be recharged.

36 Review: 6. The voltage produced by a cell is determined by the cell materials. 7. A voltaic cell can be constructed from almost any two unlike metals and an electrolyte of acid, alkali, or salt. 8. Voltaic cells depend on the movement of ions in a solution to produce electricity.

37 Review: 9. The amount of current a cell can provide is determined by the area of the cell plates. 10. Primary cells are often rated in milliamperehours or watt-hours. 11. The amount of energy a battery can contain is called its capacity or energy density.

38 Review: 12. When cells are connected in series, their voltages add and their ampere-hour capacities remain the same. 13. When cells are connected in parallel, their voltages remain the same and their ampere-hour capacities add.

39 Review: 14. Cells or batteries of different voltages should never be connected in parallel. 15. Solar cells produce electricity in the presence of light. 16. Thermocouples produce a voltage when the junction of two unlike metals is heated.

40 Review: 17. Thermocouples in series produce a higher voltage and are called thermopiles. 18. The piezoelectric effect is the production of voltage by pressure.