DIRECT-CURRENT DYNAMOS AND MOTORS. 
_ Total resistance of shunt circuit: 
gain 
T= a ae 60 ohms. 
Resistance of field regulator: 
60 — 56 == 4 ohms. 
Weight of shunt winding: 
wt, = 4X 77 X 40 X 2.54 X .0051 = 159.5 lbs, 
Total wei ght of winding: 
Wm = 1594 + 304 = 190 lbs. 
CALCULATION OF EFFICIENCIES. 
8i. Electrical Efficiency.—The electrical efficiency, or, as 
it is sometimes called, the economic coefficient of a dy- 
namo, is the ratio of its useful power to the total electrical 
power in its armature. The total electrical power is the 
sum of the useful power and of the power losses due to 
the armature and field resistances; hence the electrical 
efficiency of a generator: 
We Ww (56) 
El. Ef. = yn = paaopae 
and that of a motor: 
_ WwW _ W— (wa + Wn) 
El. Eff. = y= W sorts keies (57) 
where W = electrical power at terminals of machine; 
W’ = electrical power active in armature; 
W, = power absorbed by armature winding; 
Wm = power used for field excitation. 
In the case of a generator, W is the output available at. 
the brushes, while in a motor it is the total power deliv- 
ered to the terminals, that is, the intake of the motor. 
