Shunt-wound motors are superior to series wound
for electric boats and should be seriously considered
for all boat designs that do not use a permanent
magnet motor.<br><br>(1) series wound motors have
highest torque at lowest speeds, the opposite of what we
need in electric boats, shunt wound motors are
superior in this respect. Too high torque for a given
speed is not desirable because it wastes
energy<br><br>(2) shunt wound motors can use cheaper control
systems because controlling the constant field power is
much easier than controlling the 20 X higher power of
the armature <br><br>(3) shunt wound motors are often
used for regeneration, this is their main
attribute<br><br>(4) a 48 V shunt wound motor (hp 2.7 to 11.50) was
Yamaha's choice for its golf cart that uses regenerative
braking <br><br>(5) BTW, the Bombardier (small electric
automobile) NEV uses a 72V shunt wound ADC motor with a
Curtis regenerative controller.<br><br>(6) those in the
electric auto industry often use shunt wound motors of
less than 100 V at high horsepower because of the
regenerative braking available from these. It is hard to find
controllers advertised for this purpose to individuals
because of legal reasons (when the car crashes, blame the
controller maker for faulty brakes) and I understand that
controller makers may not sell regenerative controllers to
individuals for that reason.<br><br>(7) the permanent magnet
motors are limited to having a fixed magnetic field that
is not always optimum for lower speed operation,
Lynch in fact just got a patent on adjusting the
permanent magnetic field mechanically, something that shunt
wound does electronically.<br>If the shunt magnetic
field sucks out 5% extra energy then the motor would be
5% less efficient this is a real deficiency but
needs to be compared in an overall context. I myself
prefer a permanent magnet rare earth motor, but if I use
an electromagnet motor, I would choose shunt wound
for boat applications rather than series
wound.<br><br>(8) the rare earth magnet motors will rapidly lose
magnetism at overspeed conditions, although I cant forsee
this happening with a permanently loaded motor it does
happen in some (certainly unusual) situations. In any
event, I am not suggesting that shunt wound is better
than PM, only that it is better than series
wound.<br><br><br>Why doesn't the Electric Boat Association of the
Americas include a panel discussion about the merits and
demerits of each type of motor for its Maryland meeting
this summer? I see a bifurcation of any discussion
into two categories of motor: (1) 3-10 hp motors
designed for lowest cost performance (less than $1,000 per
motor, not including controller); and (2) 3-10 hp motors
designed for best performance, (unlimited cost, but
generally less than $5,000) <br><br>What do you say Ken
Matthews?
