You can get this on a common / ground lead and a power lead that
is hooked to the internal switch. The switch is in the start winding
at dead stop. Once turning fast, the switch flips and the run winding
is powered and the start is turned off. It is a Single Pole, double
throw switch that is controlled my speed.

Having a phase shifted internal winding gives you on a scope a waveform
and the non-shifted is only the power line. The run doesn't get anything.

The funny motor you are talking about is a milk station that has

A neutral/GND and two Legs of xxx volts that are really 2 legs of 3
phase.

I have 2 phase on my property. Two Highlines and I could have 3 phase
if I wanted with three transformers. I created my own from Single phase.

Martin

On 12/3/2017 10:41 PM, DoN. Nichols wrote:
On 2017-12-03, Martin Eastburn wrote:
I would not call a cap start motor a two phase at all.

Call it a "temporary two phase", as that is present only as the
motor is starting, and is generated by the start cap.

I would call it a dual winding single phase. The starter winding -
large diameter short winding with a cap - dumps the AC power through
the winding as XL is canceled by XC for the tech guys.

Yes, two windings, but one gets standard phase, and the other
gets shifted phase, by the XL and XC causing a shift. This provides a
second magnetic field at an angle to start the motor spinning. You
*can* start the single phase motor with just one widing, if you have a
way to spin it just before you switch on power -- such as a rope wound
on the shaft.

The run winding is used once up to speed and an internal switch throws
at speed - switching run in and start out.

Not quite. The inertial (also internal) switch switches the
start winding out, but the run winding is connected full time -- as long
as there is power to the motor.

Look at the inertial switch when you have a motor open. It
only has the contacts to open the start winding -- not any more contacts
to close the run winding.

Or -- just apply an ohmmeter to the motor from outside (and with
AC power disconnected, too, to keep from frying the ohmmeter). It will
draw current and show a fairly low resistance. If the run winding were
open, you would only see a swing of the needle (if a meter) or a short
display of low resistance moving slowly to infinite resistance, as the
start cap charges. (Well ... some leakage in the cap, so you won't
really get all the way to infinite, as a perfect capacitor would.)

If you apply power *only* to the start winding, you still lack
the shifted phase relative to the run winding, so the motor still won't
start, without something external to spin it up. But, because it is
sitting there drawing lots of current, it *will* blow up the start cap
in short order. :-)

When the power company runs low voltage - starter winding is used
longer, meaning more power used and then the run is enabled.

And then the start winding is switched out, leaving just the run
winding which was already enabled.

Now -- I grant that this is not a precise phase relationship
between the two windings -- dependent on the value of the cap and the
inductance of the winding -- as well as the frequency of the AC applied
to it.

Two phase is 2 of 3 phase in a Delta wiring of a 3 phase motor.
It is called an "Inverted V" or lost leg.

This is when the phases are 120 degrees apart. There are also
two phase power lines (uncommon these days) which have a 90 degree phase
relationship -- and a tricky transformer circuit can convert between
true two phase and true three phase -- either direction. I forget the
full name of it, but 'T' is part of the name.

This is a basis of very high rel 3 phase. Input and output are 3 phase.
If a phase is lost on the input the output has 3 phase at 66% power IIRC.

One could in theory loose two one inside and outside. Dropping more,
but still running just fine. Hospitals and Police/Mil run these like
this in case of attack.

Understood -- but this is still talking about phases shifted 120
degrees relative to each other. So you could call them "partial three
phase". The two phase for motor starting is different, with 90 degrees
being ideal, but usually not hit precisely.

Enjoy,
DoN.