120 DIRECT-CURRENT DYNAMOS AND MOTORS. 
Series-wound motor: 
Com. Rf, = HO — LO re + rm’) tw + We + we] 
Com. Eff. = 
EG Pg es 
mesjaeonhi ie motor: 
Ce, Ta + Caan” + Wn twee + w), 
EHC “(4Q) 
Compound-wound motor: 
Done at. = EC—[Cw(r. +Tre V+ Conran” +Wr+We-twre] (TA) 
_ LC 
86. Friction Losses in Dynamo-Electric Machines. 
—In the above formulas all the quantities are known 
from the previous calculation of the machine, except the 
amount of power. lost by friction; the latter will not be 
accurately known until the machine is actually built, and 
must, therefore, here be assumed. Average values of we 
for various sizes of machines, as patersd from experi- 
ence, are given in Table 29, 
TABLE 29. 
AVERAGE FRICTION LOSSES IN DYNAMO-ELECTRIC 
MACHINES. : 
Capacity Average Friction Loss Friction Loss 
of Dynamo, in Watts. in per cent. 
in Kilowatts, We of Output. 
<1 20 20% 
25 4() 16 
a) 60 12 
yi ee 100 10 
3d. 400 8 
10. 700 rE 
25. 1500 6 
pa 2500 5. 
100.. ~ 4000 4 
500. 17500 34 
1000. 30000 3 
5900, 1250006 24 
