On 2008-05-21, Steve Lusardi wrote:
Andy,
If the motor is an induction motor and single phase, rotation often can be
changed by reversing the armature end for end. This is especially true with
centrifugally switched, shaded pole starting.

It is *only* necessary for the shaded pole starting -- though I
have move the shading rings on clock motors to make them run in reverse.

Swapping the wires on the
start capacitor will not change the start direction on capacitor start
motors.

Agreed -- for the capacitor only.

Reversing single phase motors have two start windings, one for CW
and one for CCW.

*No*. At least not for single-phase motors of the horsepower
range needed for machine tools.

For a dual-voltage motor, you have three windings (beware, the
numbers which I have used to label the windings are for my convenience
in describing it, and are not likely to be used on commercial motors):

(1) o-----WWWWWWWWWWWWWWW---------------o (2)

(3) o-----WWWWWWWWWWWWWWW---------------o (4)
___
(5) o-----WWWWWWWWWWWWWWW---)|-o o------o (6)

Windings (1-2), and (3-4) are the two run windings. winding
(5-6) is the start winding -- with the centrifugal switch and the
capacitor.

To run at the lower voltage, you connect (1), (3), (5), and (L1)
together, and (2), (4), (6), and (L2) together.

To reverse it, you interchange where (5) and (6) are connected.

To run at the higher voltage, you connect:

(L1) to (1)

(L2) to (4)

(2) and (3) to (5)

Then:

To select one direction of rotation, you connect (6) to (L1) (1).
To select the other direction of rotation, you connect (6) to (L2) and (4).



Direction is determined which start winding is engaged with
a switch.

No! Only one start winding, two run windings, which are
connected in parallel to run at the lower voltage, or in series to run
at the higher voltage. The start winding is only designed for the lower
voltage, but by connecting one end of it to the junction of the two run
windings connected in series for high voltage operation, you have half
the applied voltage available between that point and either end, and
switching the free end of the start winding from one end to the other is
equivalent to reversing it -- but needs fewer switch contacts to
accomplish the task.

Motors that have only a single start winding can only be reversed
by rotating the run field winding. This can only be done if the end plates
are identical.

No -- as long as the start winding (with the capacitor and
centrifugal switch) is brought out as its own independent wires, all
that is needed is to reverse either the start winding or the run
winding, assuming a single voltage motor.

And reversing the field can be awkward with a centrifugal
switch, because part of it is mounted on one end of the rotor.

Enjoy,
DoN.

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