DIRECT-CURRENT DYNAMOS AND MOTORS. 107 
Number of layers: ——— = 
The height occupied by these 30 layers is 
30 x .041 = 1.24 inches, 
which gives a winding depth of about 14 inches, as taken 
above. 
There being 30 layers of 300 turns each, or 9,000 turns in 
all, in each coil, the total length of wire in both coils is: 
11} X. z 
12 
hence, the shunt resistance at 20° C., according to Table 
28: 
2 X 9,000 x = 54,200 feet; 
rsh = 54,200 x .00804 = 436 ohms, 
which at 55° C. (25° + 30°) amounts to 
ren’ = 486 X 1.14 = 498 ohms. 
The actual shunt current is, therefore: 
500 
Cen = 798 
which multiplied by the number of turns gives the actual 
excitation: 
AT = 2 X 9,000 X 1 = 18,000 ampere-turns. 
This is about 2 per cent. in excess of the magnetizing 
force needed. 
The total weight of the insulated wire in both coils is, by 
Table 28 : 
Wty = 54,200 X .0041 = 222 pounds, 
or 111 pounds on each magnet. 
= 1 ampere, 
Though not excessive, this is a somewhat greater weight of 
wire than would ordinarily be used on a machine of this 
kind. This is due to the fact that the length of the arma- 
ture is rather small for a bipolar machine, but was so 
chosen in order to adopt the same armature for the 4-pole 
