Lead-acid cells and batteries

Chapter Lead-acid cells and batteries

Teach Yourself Electricity and Electronics Third Edition Book
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Teach Yourself Electricity and Electronics Third Edition Book

  • to make a battery, the resulting voltage will be about 8.1 V rather than 9 V. One addi-tional cell can be added to the stack, yielding about 9.45 V.There has been some decrease in the popularity of mercury cells and batteries inrecent years. This is because of the fact that mercury is highly toxic. When mercurycells and batteries are dead, they must be discarded. Eventually the mercury, a chemi-cal element, leaks into the soil and ground water. Mercury pollution has become a sig-nificant concern in places that might really surprise you.Lithium typesLithium cells have become popular since the early eighties. There are several variationsin the chemical makeup of these cells; they all contain lithium, a light, highly reactivemetal. Lithium cells can be made to supply 1.5 V to 3.5 V, depending on the particularchemistry used. These cells, like their silver-oxide cousins, can be stacked to make bat-teries.The first applications of lithium batteries was in memory backup for electronic mi-crocomputers. Lithium cells and batteries have superior shelf life, and they can last foryears in very-low-current applications such as memory backup or the powering of a dig-ital liquid-crystal-display (LCD) watch or clock. These cells also provide energy capac-ity per unit volume that is vastly greater than other types of electrochemical cells.Lithium cells and batteries are used in low-power devices that must operate for along time without power-source replacement. Heart pacemakers and security systemsare two examples of such applications.Lead-acid cells and batteriesYou’ve already seen the basic configuration for a lead-acid cell. This has a solution of sul-furic acid, along with a lead electrode (negative) and a lead-dioxide electrode (posi-tive). These batteries are rechargeable.Automotive batteries are made from sets of lead-acid cells having a free-flowing liq-uid acid. You cannot tip such a battery on its side, or turn it upside-down, without run-ning the risk of having some of the acid electrolyte get out.Lead-acid batteries are also available in a construction that uses a semisolid elec-trolyte. These batteries are popular in consumer electronic devices that require a mod-erate amount of current. Notebook or laptop computers, and portable video-cassetterecorders (VCRs), are the best examples.A large lead-acid battery, such as the kind in your car, can store several tens of am-pere-hours. The smaller ones, like those in notebook computers, have less capacity butmore versatility. Their overwhelming advantage is their ability to be used many times atreasonable cost.Nickel-cadmium cells and batteriesYou’ve probably seen, or at least heard of, NICAD cells and batteries. They have becomequite common in consumer devices such as those little radios and cassette players you canwear while doing aerobics or just sitting around. (These entertainment units are not toosafe for walking or jogging in traffic. And never wear them while riding a bicycle.) You canNickel-cadmium cells and batteries125