Ask A Scientist© Environmental Earth Science Archive

name         Moe A.
status       other
age          old

Question -   I have a motor that (reportedly) came from a cream
separator. The
nameplate reads:  McCormick-Deering
                   Intermational Harvester Co.
                   Chicago USA
                   Frame  IR6BU
                   Style  288 8415
                   Volts  110
                   Amps   2.6
                   HP 1/6   PH 1   Cyc 60
                   No. 1272150

I am cleaning up decades of accumulated cake and have disassembled
the motor.  I have never seen a motor like this.  It has a wound
rotor, terminated in a 37 segment commutator.  Two brushes spaced
about 90 degrees are shorted together, and presumably provide the
starting field.  Three small weights roll outward under centrifugal
force to press a shorting disk against the ends of the commutator
segments to (presumably) convert the wound rotor into the equivalent
of a "modern" squirrel-cage rotor, once the motor starts.

Question:  When did McC-D make this motor, or motors like it?

Question:  Are there any advantages of this design over a squirrel-
            cage to justify the higher cost, or was this a predecessor
            of the squirrel-cage design?
-----------------
It is pretty clearly a gimmick to add startup torque to an induction motor.
Purely symmetric AC induction-motors have zero torque when at zero velocity.
Shaded-pole motors have this symmetry broken a bit, but the startup torque is still too weak if there is a viscous or heavy load on the rotor.
Capacitor-start motors sound like the nearly equivalent thing today.
I cannot compare advantages in detail, but I tend to think your motor's characteristics are somewhere between
capacitor-start and shaded-pole.   I do not know the history.

Jim Swenson
=====================================================