A/C Electric Motor Compared to a D/C Motor

Joe Flemming “I felt that we should abandon the D/C motor and go with the A/C motor for the reliability, the simplicity of design, efficiency and ultimately the lower cost. D/C motors have brushes and commutators, and the part that turns is the armature or the rotor and that has windings on it including field windings. Where there is a shut wound motor or a series wound motor, the two types of D/C motors, there is quite a bit of losses. The efficiency on even a good D/C motor is seldom above 80-85 percent efficient which sounds pretty good. Now take an A/C motor, especially a 3 phase A/C induction motor there are no brushes, no commutator, there is no rotating, winding and the efficiency of a good motor starts at the high 80 percentile and goes up into the low 90 percentile. So you are talking about something like a ten percent more efficient. The other thing is that a good D/C motor will give you two to three thousand hours of life, which sounds like a tremendous amount of time, but an average A/C motor can certainly give you up in to the fifty thousand hour life, and it isn’t just the motor that wears out, it’s typically the bearings and they are easy to replace. The motors we use are regular standard off of the shelf ball bearings, deep groove permanently lubricated, sealed ball bearings, you put the motor in and you never have to worry about it. With a D/C motor in a boat you have moisture conditions which can cause corrosion on the commutator, make the brushes stick. So a D/C motor does require periodic maintenance, the three phase issue motor requires zero maintenance.”