On 8/14/2021 11:50 AM, whit3rd wrote:
> On Saturday, August 14, 2021 at 6:19:53 AM UTC-7, bud-- wrote:
>> On 8/13/2021 10:29 PM, whit3rd wrote:
>
>>> ... a winding INSIDE that single-phase powered motor generates another phase.
>>> The rotor, typically, has conductive elements (short-circuited ones, with zero voltage
>>> applied). Calling the motor 'single-phase' ignores the internal structure, just as
>>> most circuit diagrams omit that detail.
>
>> So 3-phase motors are actually 6-phase motors.
>
> The physics of motor movement make it impossible to start clockwise with
> only one phase of excitation, but 3-phase motors can work without any trickery
> (large-ish synchronous motors, for instance) internally. Or, they can be induction
> motors with internal extra phases in the rotor. The only apparent difference is
> that the synchronous motor motion locks exactly to the input frequency.
>
> All capacitor-start or capacitor-run motors also form extra phases even if the input
> power is single phase.
>

The original quote was "To produce a rotating field in a motor, at least
3 phases are needed."

My reply was that a second phase is created in a start winding to start
a single phase motor, same as what you probably just said. Phase shift
to a start winding in the stator is done with capacitors or inductance.
"At least 3 phases" are not needed, single phase motors start on 2 phases.

But more to the point, as I said, a single phase motor will run (but not
start) on only single phase. There is a "rotating field" in the stator
(but it can be considered clockwise or counterclockwise). When the motor
has started, induction works from the rotating field. "At least 3
phases" are not needed. Single phase induction motors run on a single phase.

Capacitor start induction motors use the capacitor with a start winding
only for starting. Capacitor run motors are also capacitor start (likely
a much larger capacitor), and are 2 phase.

Synchronous motors are another subject. Three phase "large-ish
synchronous motors" won't simply start across the line. They require
"trickery". Three phase induction motors don't have a problem.

bud-- <null@void.com> wrote in news:cGaSI.40954$yS5.23096@fx46.iad:

> But more to the point, as I said, a single phase motor will run
> (but not start) on only single phase. There is a "rotating field"
> in the stator (but it can be considered clockwise or
> counterclockwise). When the motor has started, induction works
> from the rotating field. "At least 3 phases" are not needed.
> Single phase induction motors run on a single phase.
>

There is a grinding wheel at work that does not start on its own and
will run in either direction, depending on the (mechanical) boost
direction one gives it at the time of energization.

On Sunday, August 15, 2021 at 6:47:31 PM UTC-7, DecadentLinux...@decadence.org wrote:
> bud-- <nu...@void.com> wrote in news:cGaSI.40954$yS5....@fx46.iad:
> > But more to the point, as I said, a single phase motor will run
> > (but not start) on only single phase. There is a "rotating field"
> > in the stator (but it can be considered clockwise or
> > counterclockwise). When the motor has started, induction works
> > from the rotating field. "At least 3 phases" are not needed.
> > Single phase induction motors run on a single phase.
> >
> There is a grinding wheel at work that does not start on its own and
> will run in either direction, depending on the (mechanical) boost
> direction one gives it at the time of energization.

Usually, that's a bit of dirt in the centrifugal switch. On a (woodwork)
table saw, a bit of sawdust. Chopstick and compressed air fixed that
without dismounting the motor, last time mine had the issue.

whit3rd <whit3rd@gmail.com> wrote in
news:840c3bea-4d1e-4ac0-8cba-59d7cbc0aa3dn@googlegroups.com:

> On Sunday, August 15, 2021 at 6:47:31 PM UTC-7,
> DecadentLinux...@decadence.org wrote:
>> bud-- <nu...@void.com> wrote in
>> news:cGaSI.40954$yS5....@fx46.iad:
>> > But more to the point, as I said, a single phase motor will run
>> > (but not start) on only single phase. There is a "rotating
>> > field" in the stator (but it can be considered clockwise or
>> > counterclockwise). When the motor has started, induction works
>> > from the rotating field. "At least 3 phases" are not needed.
>> > Single phase induction motors run on a single phase.
>> >
>> There is a grinding wheel at work that does not start on its own
>> and will run in either direction, depending on the (mechanical)
>> boost direction one gives it at the time of energization.
>
> Usually, that's a bit of dirt in the centrifugal switch.

Except in this case. This is an old antique pedistal grinder with
two wheels, and it has no centrifugal assembly in it. Better watch
which way you plug the two wire cord in as well.

> On a
> (woodwork) table saw, a bit of sawdust. Chopstick and compressed
> air fixed that without dismounting the motor, last time mine had
> the issue.
>
Probably could have freed it with a heat gun too. Tends to loosen
things like that up. Toss in a squirt or two of good ol' WD-40.

But not with this grinder.