[Electric engineering.] . thus it will now be readily seen why the watt-hourefficiency may be considerably less than the ampere-hourefficiency. If we wish to charge 50 cells in series, the dynamo mustbe capable of furnishing 50 X 2 = 100 volts at the beginningof the charging, and this voltage must be increased volts as the cells become fully charged. 50 ELECTRIC TRANSMISSION. § 15 This is usually done by cutting resistance out of the fieldof the dynamo as the charging process proceeds. If only20 cells, say, are to be charged, we will require from 40 to50 volts; and if they are to
[Electric engineering.] . thus it will now be readily seen why the watt-hourefficiency may be considerably less than the ampere-hourefficiency. If we wish to charge 50 cells in series, the dynamo mustbe capable of furnishing 50 X 2 = 100 volts at the beginningof the charging, and this voltage must be increased volts as the cells become fully charged. 50 ELECTRIC TRANSMISSION. § 15 This is usually done by cutting resistance out of the fieldof the dynamo as the charging process proceeds. If only20 cells, say, are to be charged, we will require from 40 to50 volts; and if they are to be charged from a 100-voltdynamo, enough resistance must be inserted in series withthem to take up the extra 60 to 50 volts. Hence, if thecharging current were, say, 5 amperes, there should be atleast 6-g-°- = 12 ohms resistance in series. If this were notused, the charging current would be excessive and the cellswould be injured. Cells should not be discharged to suchan extent that their pressure falls below CARE AND OPERATION OF STORAGE CELLS. 61. Installation.—Cells should be installed in a roomwhere the ventilation is good and where they may be easily inspected. They are gen-erally mounted on a heavyframework that has beenpainted with acid-proofpaint, and if the space islimited, are arranged in twoFlG- 50- or more tiers. Storage cells are heavy and the framework should be very is necessary to watch the cells to see if any of the platesget into bad condition, also to test the condition of theelectrolyte and renew it when necessary. It is important,therefore, that the cells shall be so arranged that theattendant can readily move around among them. The cellsshould be well insulated, otherwise the acid film that is sureto accumulate sooner or later may result in considerableleakage. It is a common practice to set each cell in a shal-low tray about half full of sand and then support this trayon insulators. Fig. 50 shows an oil insulator that has be
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