90 
DIRECT-CURRENT DYNAMOS AND MOTORS. 
design are as follows: J," = 1.25 inches (the gap distance - 
~ of 2 x inch being increased by 25 per cent. to allow for 
distortion), J," = 6 inches, and l/,,” = 33 inches. The 
pole space angle in this case is 223°, one-half of which is 
about 11°. Therefore, the magnetizing forces required 
in the different parts of the circuit: ; 
at, = .313 xX 30,500 x 1.25 = 11,930 ampere-turns; 
C= BL KS = 190 ee 
tm = 51 X 33 = 1,680 “« 
is 1252x240 11° _ A 
at, = 1.25'X 1 iso 1,150 ; 
Total magnetizing force: AT = 14,950 “* 
In the formula for at,, the number of turns must here be 
multiplied by 2, because in a four-pole machine there are 
4 parallel armature circuits, hence in formula (21) the 
number of pairs of circuits has the value n, = 2. 
69. Calculation of Ampere-Turns for Four-Pole 
Toothed-Armature Dynamo.—For the toothed- 
armature design the lengths are /,” = + inch, 1,” = 74 
inches, and /,,” = 26 inches; and the angle of brush lead 
is about 6°; hence, we have: 
at, = .313 x 45,000 xX 4. = 3,520 ampere-turns; 
at,’ = 700 X2 =1,400 “ « 
tet x 31 x 54 ae. ENO re Ae 
at, = 651 X 26 = 1,330 “«  « 
2 250 X 240. 6 Pete 3 
at. = -1.26 X ETE CITA: 180 630 
Total magnetizing force: AT = 7,050 ampere-turns, 
Prinicd.in U.S.A, 
