2 Engineering
2.9 Single-phase AC motors
40 DC1-S…20…, DC1-S…OE1 Variable Frequency Drives 05/21 MN040058EN www.eaton.com
However, the special characteristics behind the way the various AC motors
are made and operated, as well as their technical principles and design
aspects, must be taken into account, and a distinction needs to be made
between the following types:
• Split pole motor,
• Split-phase motors
• Capacitor-start/induction-run motors
• Capacitor motor (PSC-Motor),
• Three-phase motors run from a single-phase supply
(Steinmetz connection)
• Capacitor-start/capacitor-run motors (not allowed for DC1-S…)
2.9.1 Split pole motor
Figure 13: Shaded-pole motor
In shaded-pole motors, the magnetic field produced by the main winding
(stator winding) induces a lagging magnetic field in the short-circuited
shading coil (auxiliary winding), which is displaced in space. This elliptic
rotating field is heavily load-dependent (slip of approximately 7 to 10 %) and
is defined to a significant extent by the shaded poles’ saliency. Accordingly,
the starting torque will only be around 25 to 70 % of the rated torque, while
the efficiency will be approx. 30 %.
As a result of their design, shaded-pole motors cost less and have a much
smaller frame size than capacitor-start/capacitor-run motors with a
comparable output. Shaded-pole motors are used predominantly for short-
time operation at outputs of up to approximately 300 W, and their quietness
and long lifespan, combined with the fact that they are maintenance-free,
make them the motor of choice for small, direct-drive axial and radial fans
and blowers.
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