112 DIRECT-CURRENT DYNAMOS AND MOTORS. 
The four series coils being connected in parallel, the 
current in each coil is 
240 + 4 = 60 amperes, 
while the magnetizing force per magnet is 
2,430 + 2 = 1,240 ampere-turns; 
hence, the number of series turns per coil: 
1240 
fie — 60 ~ — 21. 
The size of the series field conductor is: 
d,,” = 60 X 1,000 = 60,000 circular mils, 
or 3 No. 7% wires. 
The series winding is usually wound upon the core first. 
Assuming it to occupy a height of 4 inch, the mean length 
of one turn is: 
1,” = (68 + 4) X a = 22.4 inches, or 1.87 feet. 
There being on each magnet 3 coils in parallel, each hav- 
ing 21 turns, the joint series resistance (four magnets in ~ 
parallel) is therefore found: 
ee RL X 1.87 X 10497 
date 3x 4 
or .00163 X 1.12 = .00183 ohm at 50°C. 
Hence, the total power loss in the series winding: 
240° > .00183 = 105 watts. 
Since the diameter of No. 7 wire is .154 inch, each layer 
will hold 
= .00168 ohm at 20° C., 
(4 — 4) + .154 = 21 turns, 
and there will be 
(21 X 3) + 21 = $ layers, 
occupying a height of 
pee 3X .154 = } inch. 
This, ‘according to Table 2%, leaves a winding depth of 
~. 
