DIRECT-CURRENT DYNAMOS AND MOTORS. 109 
The number of turns required with the above shunt cur- 
rent is: 
7,05 
i = 2,480, or 1,240 turns per core. 
T= 
The total number of ampere-turns as found from formu- 
las (37), (42), (43), and (45) must in a multipolar 
ring machine be supplied to each two cores, as the 
various pairs of cores form a number of parallel magnetic 
circuits. In order to obtain a total number of AT 
ampere-turns, each of these parallel circuits must there- 
fore be wound with AT ampere-turns. 
Since the number of turns per layer is 
34 + 071 = 44, 
there must be 
1,240 + 45 = 28 layers, 
making a winding depth of 
28 X .071 = 2 inches, 
not including the core-insulation, or about 24 inches total. 
The resistance of the four magnet coils in series is: 
Pera 45. x 99 y (OF +78) x7 x .00252 
= 29 ohms at 20° C., 
or . 29 X 1.14 = $3 ohms at 55° C. 
The actual shunt current required to produce the desired 
number of ampere-turns is: 
eet 2 iene 
Csn ae ee 2.8 amperes; 
hence, the total resistance of the shunt circuit: 
125 
387 44.7% ohms, 
which makes the resistance of the regulating rheostat 
44.7 — 33 = 11.7 ohms. 
ns eee iy RY, 3 
oN ETT NY ec pies L LABGRATARY: 3 
. acu REI | * py ry 
