TWO PHASE MOTOR

[bernardgreen]

Are you saying that all the "two-wire" motors I've seen actually have two windings

Two wire Induction motors ( as opposed to motors with brushes and a commutor ) will have at least two out of phase magnetic poles.

These can be either

two separated windings with a capacitor in series with one

or

a single winding and one or more "shaded magnetic pole(s) " which are created by shorted turns of copper around part(s) of the magnetic path.

The shading coils delay the magnetic flux thus creating a pseudo magnetic phase and hence a "rotating" magnetic field.

 

[bernardgreen]

I don't understand the possible orange connection in this sketch unless it's a dual voltage motor,

The orange connection is not necessary for the motor to operate on the voltage between L1 and L2. ( single phase motor fed from a split phase supply ).

One use of the orange connection is when the motor is used to create a local Neutral for items that require only 120 volt ( one half of the split phase ) such as control gear and mayb lighting.

 

[JohnW2]

Two wire Induction motors ( as opposed to motors with brushes and a commutor ) will have at least two out of phase magnetic poles. These can be either
two separated windings with a capacitor in series with one ... or ... a single winding and one or more "shaded magnetic pole(s) " which are created by shorted turns of copper around part(s) of the magnetic path.

Ah, thanks. That has certainly shaken up some of the dust in my long-term memory - "shaded pole motors" are, indeed, a concept with which I am (or, at least, 'once was'!) familiar!

Kind Regards, John

 

[SUNRAY]

The orange connection is not necessary for the motor to operate on the voltage between L1 and L2. ( single phase motor fed from a split phase supply ).

One use of the orange connection is when the motor is used to create a local Neutral for items that require only 120 volt ( one half of the split phase ) such as control gear and mayb lighting.

Ah yes, Dansette record players...Pair of PCL86's and 27V for the heaters. Hope that's right from the memory bank of late 60's. Some versions simply ran in series with the motor, other had the tap off.

 

[SUNRAY]

a 'hidden' start capacitor?
Kind Regards, John

No they don't all use a capacitor, but as a general rule (which has become less relevant over the years) powerful non-com motor have had a cap - or other device to create a phase change.

A point of clarification, In the diagrams [bernards and mine] the capacitor is not a starting device.
It is a device to give a phase shift to run the motor, if the cap is removed whilst the motor is running it is very likely to run very lumpy and eventually stall. Not all motors will do this but I've not found one which will run without it.

 

[JohnW2]

A point of clarification, In the diagrams [bernards and mine] the capacitor is not a starting device.
It is a device to give a phase shift to run the motor, if the cap is removed whilst the motor is running it is very likely to run very lumpy and eventually stall. Not all motors will do this but I've not found one which will run without it.

Thanks. Yes, that also stirs up some dusty in my long-term memory - as I said, it a very long time (many decades) since I last had any reason to know much about motors!

... so (in an attempt to refresh some of that lost memory!) what does that mean in terms of small 'two-wire' motors which don't have any visible 'run' capacitor (and certainly no switched 'start' capacitor) - are they shaded-pole motors, is there a 'hidden' run capacitor, or what? ... or are they, perhaps, synchronous motors?

Kind Regards, John

 

[SUNRAY]

Thanks. Yes, that also stirs up some dusty in my long-term memory - as I said, it a very long time (many decades) since I last had any reason to know much about motors!

... so (in an attempt to refresh some of that lost memory!) what does that mean in terms of small 'two-wire' motors which don't have any visible 'run' capacitor (and certainly no switched 'start' capacitor) - are they shaded-pole motors, is there a 'hidden' run capacitor, or what? ... or are they, perhaps, synchronous motors?

Kind Regards, John

As far as I'm aware they will be shaded pole (thanks to Bernard for reminding me of the terminology), I have seen 2 coils on 2 cores [imagine 2 sets of bernards drawing] working on a single rotor for very low power applications.

 

[bernardgreen]

Syncronous come in a variety of types

Some of the cheapy ones use a permanent magnet rotor and two sets of magnetic pole pieces and a single coil. A strip down can be seen HERE .