Compound motor

It is possible to arrange for part of the field  coil to be in series with the armature and part in parallel

This gives rise to a motor with a mix of the characteristics of shunt and series connected motors, the mix depending upon the armature connection point in the field winding.

Power production
 
The mechanical power produced by a motor is:
 
P = T . ω
 
(power is in watts if torque is N.m and ω in rad/sec). Some of this will be lost due to friction and windage. The remainder is available as mechanical output power. The input electrical power that is converted to mechanical power is that due to the product of the back emf and the armature current.

Hence

P = e. I_a


Note that e is not equal to the applied voltage, V. Some electrical power is dissipated due to the armature resistance and field coil resistance. (In an ac motor, other losses occur due to magnetisation and eddy current losses).