Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . s around them, each consisting of anumber of turns of phosphor bronze wire. Mica is interposedbetween the band wires and the armature wires, and theformer soldered together, thus producing a solid band. Acommutator with 8 bars will be required since there are 8 coilsand the coils are to be joinedin series. Connect the be-ginning of coil No. 1 to bar1 and the ending of coil to bar 2, Fig. 344 ; the be-ginning of coil No. 2 to theending of coil No. 1 at bar2; the ending of coil No
Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . s around them, each consisting of anumber of turns of phosphor bronze wire. Mica is interposedbetween the band wires and the armature wires, and theformer soldered together, thus producing a solid band. Acommutator with 8 bars will be required since there are 8 coilsand the coils are to be joinedin series. Connect the be-ginning of coil No. 1 to bar1 and the ending of coil to bar 2, Fig. 344 ; the be-ginning of coil No. 2 to theending of coil No. 1 at bar2; the ending of coil No. 2to bar 3 and to the beginningof coil No. 3, and so on untilfinally the ending of coil 8will connect to the be-ginning of coil 1 at bar coils are thus all in Series around the armature ; Fig. 344.—Connecting the Armaturethe commutator bars form- Coils to the Commutator, ing the connecting links between the coils. Many more turnscould be wound per layer, and more layers per division, toincrease the induced E. M. F. After the first set of coils iswound a second set may be wound on top of them, with. ARMATURES. 361 proper insulation between them ; 16 bars would have beenrequired had this method been adopted in Fig. 343. Themethod of varying the winding according to the potentialdesired is illustrated in Fig. 345, which represents the numberof wires per coil on an 8 H. P. dynamo when it is wound for125 volts, as in A ; 250 volts, in B ; 500 volts, in C. The sizeof the wires decreases as the voltage increases, since for thesame power the current will be less, and the turns increase indirect proportion to the voltage, there being 3, 6, and 12 turns
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