36 
DIRECT-CURRENT DYNAMOS AND. MOTORS. 
338. 
339. 
340. 
341. 
B43. 
344. 
345. 
346, 
Give approximate formula for the total E. M. F. of an 
ordinary compound dynamo. 
What is the formula for the approximate total E. M. F. 
of a 5 per cent. over-compounded dynamo? 
How is the cross-section of the series field wire of a com- 
pound dynamo determined ? 
In which case must the size of the series wire, obtained by 
the rule referred to in the preceding question, be in- 
creased? 
By means of Table 28, Instruction Book, determine the 
number of turns of No. 8 wire that can be put in each 
layer of a coil 124” long. | 
How many turns of No. 14 wire can be wound in a coil 
space 8?” long and 14” high? 
A magnet of 17” diameter is wound with 15,000 turns 
of No. 19 B. & S. wire to a height of 1% inches; find 
the bare and covered weight of the wire and its resist- 
ance at 20° C. 
Calculate a series winding for the machine given in Ques- 
tion 295 (Part 3), supposing that its armature is 
wound for 5,000 volts and 10 amperes, and assuming 
that the magnetizing force required for its excitation 
was obtained as 20,000 ampere-turns; the length of 
each magnet core is 22 inches; allow a wire cross-sec- 
tion of 1,650 circular mils per ampere. 
The machine considered in Question 295 is to be shunt- 
wound for an output of 125 volts and 480 amperes; the 
winding to be calculated for a magnetizing force of 
20,000 ampere-turns and a temperature increase of 20° 
C.; depth of magnet winding 1} inches; allow a drop 
of 15 per cent. for regulating resistance, and take as 
cooling surface the cylindrical portion of the magnets 
only. 
