118 



THE WORLD'S ADVANCE 



parallel groups, each consisting of five or ten 

 cells in series. If you desire greater strength, 

 for a few moments only, you can put the two 

 coils in parallel rather than in series with each 

 other. Use No. 18 single cotton covered wire, 

 getting about 70 turns per layer, and 12 layers 

 per spool. Each spool will require slightly 

 over two pounds of wire. Make the flanges 

 of the spools at least H" deep. 



FLICKERING OF LIGHTS SUPPLIED 

 BY GENERATOR. 



(4) R. R., Humboldt, Kans., asks: 

 Q. i. What is the cause of flickering in the 

 electric lights operated from a certain direct 

 coupled dynamo? Latter is apparently in 

 good shape, and gives no volts and 30 am- 

 peres. 



A. i. The causes of flickering may be 

 many, some of them hard to find, and even 

 to remedy. It would be interesting to know 

 the name of the manufacturer of the gen- 

 erator. In a certain case known to the writer, 

 in which there were two large generators in 

 an isolated plant, the causes of flickering 

 were so involved in the design as to be irre- 

 mediable, and led to the "scrapping" of the 

 machines. Too few commutator segments, 

 irregular spacing of the brushes, unsymmetri- 

 cal armature winding, unequal spacing of the 

 poles, poor centering of the armature, and 

 poor engine regulation, may be stated as being 

 concerned in the cause. You should certainly 

 seek to remedy the cause, and any progres- 

 sive manufacturer ought to be anxious to re- 

 move all causes of criticism. 



PIG ALUMINUM AND INDUCTION 

 MOTOR DATA. 



1 

 asks: 



S. McD., Brandon, Manitoba, Can., 



Q. i. From what firm can he purchase 

 "pig" aluminum? 



A. i. In the States the principal makers 

 are the Aluminum Company of America, with 

 main offices in Pittsburgh, and works at 

 Niagara Falls. From them you could un- 

 doubtedly obtain the address of the nearest 

 Canadian firm with which they are affiliated, 

 and thereby save you the payment of import 

 duties. 



Q. 2. What general dimensions and wind- 

 ing should be followed for making an induc- 

 tion motor of i/io horsepower and 3,000 rev. 

 per min.? 



A. 2. As you do not state the voltage and 

 frequency, we are at loss to make any relia- 

 ble calculations. Possibly you desire a no- 

 volt machine, and the statement of speed sug- 

 gests that you have a supply at 50 cycles, 

 for with a 2-pole field that would yield the 

 synchronous speed. With 60 cycles the speed, 

 allowing for "slip," would be about 3,300. It 



would be worth while to know what range of 

 materials you may have at your disposal, for 

 some accommodation to meet them may be 

 possible. A stator having an outside diameter 

 of 6", inside of 3^", the stack of sheet iron 

 being iy 2 " thick, would be a good trial size. 

 Have 24 slots, the proportions being about as 

 given in Watson's articles. About No. 20 

 wire may be used, but arranged for two poles 

 rather than four. 



Q. 3. In making such a motor is it neces- 

 sary to have any external switches, resistances, 

 reactances, etc.? Such cumbrous adjuncts 

 seem to be omitted from ordinary makes. 



A. 3. While it is true that such starting 

 devices make additional expense, and espe- 

 cially in small sizes of motors are to be 

 omitted if possible, you must face the realiza- 

 tion that their omission may mean the reten- 

 tion of certain factors that lessen the regular 

 operating efficiency. Just as in the direct 

 current motors, if you have no starting rheo- 

 stat, it means that the motor is wound with 

 an inherent high resistance, and has a lower 

 working efficiency than otherwise. Certainly 

 in the case of all large motors, also those used 

 for railway and elevator service, plenty of 

 external devices are involved, and in their 

 design no small engineering skill is shown. 

 You can design a motor poor enough to per- 

 mit the absence of such devices, or good 

 enough to require them, thereby permitting 

 their losses to be maintained during the start- 

 ing operations only. 



GENERATOR DATA. 



(6) W. L., Riverside, N. Y., asks: 

 Q. i. How to wind a laminated field mag- 

 net and armature so as to get from 6 to 12 

 volts. Armature is i^" in diameter, 2J4" 

 long, with 12 slots 5/16" in diameter. 



A. i. In consequence of the inability of the 

 laminated structure of the field magnet to 

 hold any "residual" magnetism, you cannot 

 make the machine self -exciting. If it is to 

 be used for charging storage batteries, no diffi- 

 culty, however, will be experienced, for in that 

 case the electromotive force of the cells may 

 be relied upon to give the initial start. In 

 other cases you would find it necessary to 

 clamp the sheet iron between two cast iron 

 plates, say H" thick, and of the same shape 

 as one of the punchings. You might use No. 

 22 wire on armature, No. 25 on fields. 



QUESTIONS ANSWERED BY MAIL. 



For the benefit of those wishing^ to have 

 their questions answered by mail without the 

 delay involved in answering them in these 

 columns, there is a special service offered to 

 readers only. Questions will be answered by 

 mail within a few days' time if they are ac- 

 companied by the fee of fifty cents. If the 

 answers involve ^extensive calculation and re- 

 search, the inquirer will be advised r* * n * La 

 fee. 



