Resistance, and Self- Capacity of Magneto Windings. 59 



In an experiment using' a certain armature coil, without 

 brass end-plates or other metal parts, the following data 

 were obtained : — 



/ = 6'2 x 10 4 — per sec. 

 I = 7-85 xl0~ 2 amp. 

 H eq = 2*5 ohms. 



R 2 = 2200 ohms (without iron core). 

 C = 2100 picofarads. 

 C 2 = 50 



Thus equivalent series resistance for charging current 

 r C2 =l*25 ohm, and therefore the series resistance equi- 

 valent to dielectric loss, R ! eq — R e q — r e? =l*25 ohm. Equi- 

 valent dielectric resistance for particular case of magneto 

 secondary winding 



^ d ~ co 2 C'R' eq 



= 1*2 xlO 6 ohms. 



Loss at / = 6'2xl0 4 — and Vmax. = 140 volts = 7 -7 

 x 10~ 3 watt. Assuming loss a fY 2 max.*, the amount 

 dissipated during one quarter period prior to the passage 

 of the spark when V max. = 10 4 volts, is 1*57 X 10~ 4 joule, 

 ?'. e. only 6 per cent, of ^C 2 V 2 2 . Inclusion of the loss 

 arising from the charging current in the winding increases 

 this percentage to 7. 



(7) Calculation of Energy Loss in Primary and Secondary of 

 Magneto prior to the passage of the spark. 



In calculating the energy loss in a magneto, we are only 

 concerned with the energy which is lost during the time 

 which elapses between the breaking of the primary current 

 and the passage of the spark. The following method of 

 calculation is approximate, but it serves to show the order 

 of magnitude of the loss. 



Let V 2 = secondary voltage when spark passes. 



O2 = self-capacity of secondary ■+• capacity of leads 



to spark gap. 

 R e2 = effective resistance of secondary. 

 Irms = root mean square of current. 



Then current in secondary at any instant is i 2 = C 2 — r^ . 



* See G. E. Bairsto, Proc, Roy. Soc. A. vol. xevi. pp. 363-382 (192W. 



