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The Electrical Review. The Electrical Review Book Review:. The Model Engineer and Electrician. The electrolyte is a paste of manganese dioxide and carbon.
Zinc-carbon cells are inexpensive and are usable at moderate temperatures, and in applications where the current drain is from moderate to high. They do not work well in extremely cold environments.
ALKALINE Alkaline cells have granular zinc for the negative electrode, potassium hydroxide as the electrolyte, and a substance called a polarizer as the positive electrode. An alkaline cell can work at lower temperatures than a zinc-carbon cell. It lasts a long time in low-current electronic devices, and is therefore preferred for use in transistor radios, calculators, and portable cassette players.
Its shelf life is much longer than that of a zinc-carbon cell. They provide 9 V and consist of 6 zinc-carbon or alkaline cells in series.
Transistor batteries are used in very-low-current electronic devices that are operated on an intermittent basis, such as radio-controlled garagedoor openers, television and stereo remote-control boxes, smoke detectors, and electronic calculators.
One type has spring contacts on the top. The other type has thumbscrew. Besides keeping an incandescent bulb lit for awhile, these batteries, usually rated at 6 V and consisting of 4 zinc-carbon or alkaline cells connected in series, can provide enough energy to operate a low-power two-way communications radio.
For this reason, they are sometimes called button cells, although some other types of cells also have this shape. They t inside wristwatches, subminiature calculators, and small cameras. They come in various sizes and thicknesses, supply 1.
They are known to have a at discharge curve. Silver-oxide cells can be stacked to make batteries about the size of an AA cylindrical cell.
They are manufactured in the same button-like shape. The main dierence, often not of signicance, is a somewhat lower voltage per cell: approximately 1. There has been a decrease in the popularity of mercury cells and batteries in recent years, because mercury is toxic.
When discarding mercury cells, special precautions must be taken, and these precautions are mandated by laws that vary from one locale to another. If you have cells or batteries that you suspect contain mercury, call your local trash-removal department, and get instructions on how to dispose of the cells or batteries.
These cells, like their silver-oxide cousins, can be stacked to make batteries. Lithium cells and batteries have superior shelf life, and they can last for years in very-low-current applications. They provide excellent energy capacity per unit volume. LEAD-ACID Lead-acid cells and batteries have an electrolyte of sulfuric acid, along with a lead electrode negative and a lead-dioxide electrode positive. Some lead-acid batteries contain an electrolyte that is thickened into a paste.
These are sometimes used in consumer devices that require moderate current, such as notebook computers, handheld computers, and portable video disc players.
They are also used in uninterruptible power supplies UPSs for desktop computer systems. Nickel-based button cells are used in cameras, watches, memory backup applications, and other places where miniaturization is important. Flooded cells are used in heavy-duty applications, and can have a storage capacity of as much as Ah.
They have a box-like appearance. Spacecraft cells are made in super-strong, thermally insulated packages that can withstand extraterrestrial temperatures and pressures. Nickel-cadmium NICAD batteries are available in box-shaped packages that can be plugged into any equipment to form a part of the case for a device. An example is the battery pack for a handheld radio transceiver. This type of battery should never be left connected to a load after it has discharged.
This can cause the polarity of one or more cells to reverse. Once this happens, the battery will not accept a recharge and will no longer be usable. When a NICAD cell or battery has discharged almost all the way, it should be recharged as soon as possible.
These batteries are in fact preferred, because they do not contain toxic cadmium. Some engineers believe that NiMH batteries also exhibit better behavior when repeatedly discharged and recharged. Suppose you want to make a 9 V battery by stacking silver-oxide cells. How many cells will it take? How can you be sure the polarity is correct? A single silver-oxide cell produces 1.
Therefore, 6 such cells are required. It is important that all. It is also important to pay attention to the polarity when using the battery. If this is not the case, the battery should be tested for polarity with an inexpensive multimeter, available at most hardware or electronics stores. Suppose you cant nd silver-oxide button cells, but only mercury button cells are available. How many of these will it take to produce 9 V? In order to gure this out, rst divide 9 V by 1. Even if we could cut the cells apart, which we would denitely not want to do with cells containing mercury, it would not change their voltage!
In most applications, either approach will produce satisfactory results. Photovoltaics A photovoltaic PV cell is a semiconductor device that converts visible light, infrared radiation, or ultraviolet radiation directly into electricity. This type of cell is completely dierent from an electrochemical cell. Its also commonly. Photovoltaic cells can be combined into photovoltaic batteries to obtain considerable voltage and power output.
It is made of two types of specially treated material, called the P type silicon and the N type silicon. The top of the assembly is transparent so that light can fall directly on the P-type material. Metal ribbing, which forms the positive electrode, is interconnected by means of tiny wires. The negative electrode is a metal backing called the substrate, placed in contact with the N type silicon. When visible light, infrared radiation, or ultraviolet radiation strikes the boundary surface between the P type and the N type silicon known as the PN junction , a potential dierence is produced.
The intensity of the current from the PV cell, under constant load conditions, varies in direct proportion to the brightness of the light striking the device, up to a certain point. Beyond that point, the increase becomes more gradual, and it nally levels o at a maximum current called the saturation current. The ratio of. Silicon solar cells produce about 0. If there is low current demand, it doesnt take very bright light to produce the full output voltage.
As the current demand increases, brighter and brighter light is needed to produce the full output voltage. There is a maximum limit to the current that can be provided from a PV cell, no matter how bright the light is. This limit depends on the surface area of the cell. If more current is required than a single PV cell can deliver, then two or more cells can be connected in parallel.
If more voltage is needed than a single cell can produce, then two or more cells can be connected in series. For example, a 50 parallel-connected set of 24 series-connected cells provide approximately 13 V with substantial deliverable current.
Some solar panels are extremely large, covering hundreds of square meters. Although high voltages such as V can theoretically be obtained by connecting many photovoltaic cells in series, this is not practical because the internal resistances of the cells add up, limiting the current output and causing voltage-regulation problems.
If high voltage is needed from a solar panel, a device called a power inverter can be used along with a high-capacity rechargeable battery, such as a lead-acid automotive type. Power inverters are available at large department stores, home supply stores, and hardware stores.
The solar panel keeps the battery charged; the battery delivers high current on demand to the power inverter. It uses a large solar panel, a large-capacity lead-acid or a nickel-based battery, a power inverter to convert the low-voltage DC into utility AC, and a sophisticated charging circuit. Such a system is best suited to environments where there is sunshine a high percentage of the time.
Solar cells, either alone or supplemented with rechargeable batteries, can be incorporated into an interactive solar electric energy system. This requires a special arrangement with the electric utility company. When the solar. Conversely, when the solar power system supplies more than enough energy for the needs of the home, the utility company can buy the excess.
Suppose you have access to an unlimited number of identical silicon PV cells. Each cell supplies 0. You want to produce a power source sucient to operate a device that requires 12 V DC at 1 A.
What is the smallest possible PV array that will accomplish this, assuming that you have an environment where bright, direct sunlight shines when you need to use the device? When two or more identical PV cells are connected in series, the maximum deliverable current of the combination is the same as that of any one of the cells. In this case, that is 50 mA. In order to get 1 A of current, youll have to combine 20 of the series PV sets in parallel.
The resulting series-parallel array contains PV cells, and is a by matrix. In the above situation, suppose you build sets of 20 PV cells in parallel, and then combine 20 of these parallel sets in series. Will this work as well as the arrangement described in Solution , or not? This will work just as well as the arrangement described in Solution Instead of having 20 sources of 12 V, each capable of delivering 50 mA and all connected in parallel, you will have 20 sources of 0.
The two matrixes, while dierent in their interconnection geometry, produce the same results in practice. Fuel Cells In the late s, a new type of electrochemical power device emerged that is believed by many scientists and engineers to hold promise as an alternative energy source: the fuel cell. As its name implies, it derives electricity from hydrogen. The hydrogen combines with oxygen that is, it oxidizes to form energy and water.
There is no pollution and there are no toxic by-products. When a hydrogen fuel cell runs out of juice, all it needs is a new supply of hydrogen, because its oxygen is derived from the atmosphere. Instead of combusting, the hydrogen in a fuel cell oxidizes in a more controlled fashion, and at a much lower temperature. There are several schemes for making this happen. The proton exchange membrane PEM fuel cell is one of the most widely used fuel cells.
A PEM hydrogen fuel cell generates approximately 0. In order to obtain higher voltages, individual cells are connected in series. A series-connected set of fuel cells is technically a battery, but the more often-used term is stack. Fuel-cell stacks are available in various sizes. A stack about the size and weight of an airline suitcase lled with books can power a subcompact electric car.
Smaller cells, called micro fuel cells, can provide DC to run devices that have historically operated from conventional cells and batteries.
These include portable radios, lanterns, and notebook computers. Almost anything that combines with oxygen to form energy has been considered. Methanol, which is a form of alcohol, has the advantage of being easier to transport and store than hydrogen, because it exists as a liquid at room temperature. Propane is another chemical that has been used for powering fuel cells. This is the substance that is stored in liquid form in tanks for barbecue grills and some rural home heating systems. Methane, also known as natural gas, has been used as well.
Some scientists and engineers object the use of these fuels because they, especially propane and methane, closely resemble fuels that are already commonplace, and on which society has developed the sort of dependence that purists would like to get away from. In addition, they are derived from so-called fossil fuel sources, the supplies of which, however great at the moment, are nevertheless nite.
Cost is the main reason. Hydrogen is the most abundant and the simplest chemical element in the universe, and it does not produce any toxic by-products. This would at rst seem to make it the ideal choice for use in fuel cells. But storage and transport of hydrogen has proven to be difcult and expensive.
This is especially true for fuel cells and stacks intended for operating systems that arent xed to permanent pipelines. An interesting scenario, suggested by one of my physics teachers all the way back in the s, is the piping of hydrogen gas through the standard utility lines designed to carry methane. Some modication of the existing system would be required in order to safely handle hydrogen, which is lighter than methane and can escape through small cracks and openings more easily.
But hydrogen, if obtained at a reasonable cost and in abundance, could be used to power large fuel-cell stacks in common households and businesses. The DC from such a stack could be converted to utility AC by means of the same types of power inverters now used with PV energy systems. The entire home power system would be about the same size as a gas furnace. Suppose you need a rechargeable battery that can provide 12 V DC at 7.
Which of the following is the right choice? The maximum deliverable current from a lead-acid battery depends on a the mass and volume of the battery. A by series-parallel array of silicon PV cells, exposed to direct sunlight, can be expected to produce a 0. A stand-alone solar electric energy system requires a a storage battery of some sort.
If a NICAD battery is allowed to discharge completely, to the extent that the polarity of one or more of its cells reverses, what should you do? This is a set of four silicon PV cells connected in parallel. What is wrong with this circuit? The polarities should all agree, so the cells are connected minusto-minus and plus-to-plus. In the circuit of Fig. What will be the DC voltage E when the array is exposed to bright sunlight and there is no load connected?
A rechargeable cell is also generally known as a a standard cell b a lead-acid cell c a secondary cell d a fuel cell. The length of time a battery will keep its useful charge, if it is allowed to sit around and is never used to provide power to anything, is known as its a maximum deliverable time. Test: Part One Do not refer to the text when taking this test. You may draw diagrams or use a calculator if necessary. Answers are in the back of the book.
Its best to have a friend check your score the rst time, so you wont memorize the answers if you want to take the test again. The premise is false. High voltage isnt any more dangerous than low voltage, whether other factors are held constant, or not. A voltage of mV is the equivalent of a , mV. Suppose there are 5 resistors, each with a value of , are connected in series.
What is the net resistance of the combination? Suppose you are drawing a schematic diagram, and you have to make two lines representing wires cross on the page. You want to indicate that they are connected. You can do this by a. How many elementary charge units ECU are there in a volt?
The current in an electrical conductor is considered by physicists to ow from the positive pole to the negative pole. Nevertheless, in a conventional conductor, the particles responsible for the current are a negatively charged ohms. Suppose that 5 resistors, each with a value of , are connected in parallel. Suppose that 6 ashlight cells, each producing 1. What is the net voltage of the combination? In the circuit shown by Fig. Test, suppose the battery consists of 1.
How many cells are there in this battery? Test, what does the meter read, assuming it is calibrated properly and is of the correct range to give a meaningful reading of the DC in this circuit? Suppose several more neon lamps, all identical to the one there now, are connected in parallel with the battery in the circuit of Fig.
What will happen to the current drawn from the battery? It will increase in direct proportion to the number of lamps. It will decrease in direct proportion to the number of lamps. It will increase in proportion to the square of the number of lamps. How much power is dissipated by the neon lamp in the circuit of Fig. How much energy is dissipated by the neon lamp in the circuit of Fig.
A button cell would most likely be used as the main source of power for a a wristwatch. Suppose you let a 60 W bulb stay aglow continuously. Energy in your location costs 10 cents per kilowatt hour. How much does it cost to leave this bulb on for 10 days and 10 nights? Suppose that 16 resistors, each with a value of , are connected in a 4-by-4 series-parallel matrix.
Suppose a single solar cell is capable of supplying exactly 81 mW of DC power when exposed to direct sunlight. If 3 of these cells are connected in series, the resulting set of solar cells can theoretically provide a 9 mW of DC power in direct sunlight. If 3 of these cells are connected in parallel, the resulting set of solar cells can theoretically provide a 9 mW of DC power in direct sunlight. Which of the following sources of DC power can make use of hydrogen as the chemical from which the power is derived?
Electrical current is expressed in terms of a the rate of change in voltage between two points per unit time. Test, the ve symbols at the top with the arrows represent a conventional dry cells.
Test, the ve symbols at the right with the zig-zaggy lines represent a conventional dry cells. Test, the ve symbols down the middle with the single arrows and the pairs of little circles represent a fuel cells.
Test, the ve symbols consisting of large circles with ovals inside represent a light bulbs. Suppose that all ve of the components at the top of the circuit in Fig. How will this aect the performance of the whole arrangement? It wont have any practical eect. It will burn out all the components whose symbols consist of large circles with ovals inside. Test, the switches are all a open. Suppose one of the components at the top of the circuit in Fig.
Test13 is removed, leaving an open circuit in its place. Suppose that the component at the extreme lower right of the circuit in Fig. Test is removed, leaving an open circuit in its place. It will make one of the bulbs fail to glow, regardless of the status of the switches. Suppose two electrically charged objects are brought near each other, and an electrostatic force is observed that tends to push them apart.
If the objects are brought closer and closer together, the electrostatic force will a. A frequency of , Hz is the equivalent of a 0. Which of the following equations is true pertaining to the circuit in Fig. As you progress, you'll also conquer topics such as absolute value, nonlinear inequalities, inverses, trigonometric functions, and conic sections.
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