. Modern mechanism, exhibiting the latest progress in machines, motors, and the transmission of power, being a supplementary volume to Appletons' cyclopaedia of applied mechanics . f only a few volts of electromotive keep down the resistance, many collect-ing-brushes press on each end of each cylin-der. This dynamo has been used at Okerfor electroplating. 2he Forbes Dynamo has also attracted consideralile attention, on account of its enormouscurrent output for a given weight. Originally Prof. Forbes began by employing an iron diskwhich rotated between two cheeks of opposite polarity,
. Modern mechanism, exhibiting the latest progress in machines, motors, and the transmission of power, being a supplementary volume to Appletons' cyclopaedia of applied mechanics . f only a few volts of electromotive keep down the resistance, many collect-ing-brushes press on each end of each cylin-der. This dynamo has been used at Okerfor electroplating. 2he Forbes Dynamo has also attracted consideralile attention, on account of its enormouscurrent output for a given weight. Originally Prof. Forbes began by employing an iron diskwhich rotated between two cheeks of opposite polarity, the current being drawn from itsperiphery. He then doubled the parts. The next stage was to unite the two disks into onecommon cylinder, as shown at A in Fig. 82. Here the coils lying in their cases are shown insection, the dotted lines indicating the direction of the lines of magnetic force induced in theiron. These are practically closed on themselves, so that there is no external field at all. Forthis reason the inventor prefers to call this type of dynamo non-polar. A rubbing contact,for which purpose Prof. Forbes at one time used carbon brushes, and at another a number. Fig. 81.—Unipolar dynamo. 232 DYNAMO-ELECTRIC MACHINES. of sprinffv strips of metal-foil, is maintained at the two extremities of the periphery. One ofthe earlier forms of machine, with a single disk 18 in. in diameter, was stated to give ;J,117 ainjKTcs at a potential of 5-8 volts when runningat 1,500 revolutions per min. One of the latermachines, in which the armature is a cylinderof iron 9 in. in diameter and 8 in. long, is designedto give, at 1,000 revolutions per min., a current of10,000 amperes at a potential of 1 volt. Theelectromotive force of such machines increases asthe square of the diameter. The theory of theunifiolar disk machine has been given by Sir , who has shown that such a maeliine isnot self-exciting except above a certain criticalspeeil, (lej)endent on the resistance of t
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Keywords: ., bookcentury1800, bookdecade189, booksubjectmechanicalengineering
