Unit 13 Batteries and Other Electrical Sources

Transcription

1 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.

2 Typical cell and battery schematic symbols.

3 Simple potato voltaic cell.

4 Simple nickel/paper/penny voltaic cell.

5 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.

6 Electromotive series of metals list.

7 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.

8 Voltaic cells.

9 Carbon-zinc cell.

10 Mercury button cell.

11 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.

12 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.

13 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.

14 Power comparison based on size.

15 Power comparison based on type.

16 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.

17 Series-connected batteries.

18 Parallel-connected batteries.

19 Combination-connected batteries.

20 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.

21 Solar cell schematic symbol.

22 Photovoltaic circuit.

23 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.

24 Thermocouple.

25 Thermopile.

26 A safety system using a thermocouple.

27 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.

28 Piezoelectric effect.

29 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?

30 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?