While it is true that in the past wound field
(shunt wound motors) had better brushware this is no
longer true in the past 10 years or so with the newer
magnetic matierals the performance and effeciencies of PM
motors is as good or better than for wound field motors.
With a wound field motor you have to keep the field
excited at a constant voltage while supplying a variable
voltage to the armature to control the speed in order to
maintain a constant torque constant (KT). Although the
current draw is low, a few amps, this actualy will make
the wound field less effecient than a PM motor. While
it is true that if you decrease the voltage to the
field of a wound field motor the speed will increase
the opposite is true about the torque. It will
dcrease. This is exactly the oposite type of a
characteristic that you need to propell a boat. As the speed
goes up so does the torque.<br>There are a number of
manufacturers of wound field DC motors I believe that ELCO uses
the General electric motor. There is also Baldor, US
motors and Reliance Electric to name a few. The are
involved primarily with industrial motors and they 5-10 Hp
motors that you mentioed would be designed with 240 volt
armatyure and 150 Volt fields.
