PSC Motors - Schematics

Permanent Split Capacitor (PSC) Motors' Schematics

Attached are several Schematics describing the following type Single Phase Induction Motors:

Split-Phase Induction; Permanent Split Capacitor (PSC)

To discuss these items, please refer to the following Thread in the Electrical Theory and Applications Section:

Single Phase Induction Motor

Let me know if you have suggestions, questions or comments.

Scott

*** PLEASE NOTE ***
These Drawings do not include Speed Control; only Start/Stop + Forward / Reverse control.
For Speed Control PSC Schematics, please refer to the Technical Reference Section's "Menu".
Search for the link entitled: "Split-Phase 1Ø Motors: Series 3"


*** Drawings Uploaded 06/05/2008 ***

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*** NOTE ***

Either of the Two (2) "AC-IN" leads may be the System's Grounded ("Neutral") Conductor - for an L-N Circuit (i.e.: 120V, 277V);
or they may both be Ungrounded ("Hot") Conductors - for an L-L Circuit (i.e.: 208V, 240V, 480V).


*** BASIC OPERATION PRINCIPLES ***

This Motor is a Single Phase Squirrel-Cage Induction Motor: Split-Phase, Permanent Split Capacitor.

The Motor's Auxiliary Winding has a low value Capacitor in Series between the Winding and the "Opposite" side of the AC Circuit.

There is no Centrifugal Start Switch in series with the Auxiliary Winding / Capacitor, as would be normal with any other Split-Phase Motors - with the exception of the Cap. Start / Cap. Run Motor, or the Shaded Pole Motor.

The Auxiliary Winding + Capacitor remain connected to the AC Circuit thruout the entire operation of the Motor.

Starting Torque is very low, but Pullout Torque is not so bad!

Speed control of these Motors may be easilly achieved by reducing the input Voltage - either by an external means, or by an intregral Autotransformer wound into the Motor's Windings.

The Speed of the Rotor will be a result of the required True Power (Wattage) needed to drive the load on the shaft, and falling just below a "Slip Frequency" point.

*** STARTING PROCEDURES ***

To get the 1 Phase Motor's Rotor to begin spinning (as opposed to just sitting still), one "Side" of the Main Winding's Magnetic Field must be reduced in intensity. This is achieved by adding the "Auxiliary" (or "Start") winding into the Motor's Circuitry.

At Start, without the Aux. winding, the Main Winding produce an equal Field across its self + the rotor, which results in no Induced VARs (Reactive Power) into the Rotor - so the rotor just sits still.

With the Aux. Winding included to the Circuit, one "Side" of the Main Winding's Field is reduced, which allows for VARs to be Induced into the Rotor - thereby makes the Rotor start to spin.

The Rotor turns toward the "Side/End" of the Main Winding with the larger Field.

Speed increases to the point where the Rotor can develope the needed Torque / Horsepower, by drawing the necessary level of True Power (Wattage) from the Supply (Watage equates to output HP), along with the needed VARs (Reactive Power, or Volt-Amps Reactive).

Both of these Powers are contained in the "Apparent Power" (VA, or Volt-Amps)

Since the Single Phase 2 Wire Circuit has no "Polarity", reversing only the incoming leads will not reverse the Rotor's Direction.

The way the Rotor's Direction is changed is by "Reversing The Relative Polarity" of the Auxiliary Winding, as viewed by the "Relative Polarity" of the Main Winding (the Main Winding's Relative polarity does not get changed).

When this is done, the Magnetic field is reduced on the opposite end of the main Winding, so the Rotor begins to spin towards the "End" of the Main Winding with the larger Magnetic Field.
As a result, the Rotor spins in the opposite direction.

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FIGURE #1-1: BASIC PSC MOTOR CONNECTIONS:
DIRECTION = FORWARD

This Drawing shows the Permanent Split Capacitor Motor (hereafter referred to as "PSC Motor"), with Basic connection scheme for Forward Rotation Direction.


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FIGURE #1-2: BASIC PSC MOTOR CONNECTIONS:
DIRECTION = REVERSE

This Drawing shows the PSC Motor, with Basic connection scheme for Reverse Rotation Direction.


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FIGURE #1-3: BASIC PSC MOTOR CONNECTIONS:
DIRECTION = REVERSE

This Drawing shows what Fig. 1-2 actually looks like to the Rotor.

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FIGURE #2-1: DIRECTIONAL PSC MOTOR CONNECTIONS - SWITCH CONTROL:
DIRECTION = FORWARD

This Drawing shows the PSC Motor with SPDT Switches used for Forward / Reverse of the Motor.

Switches are thrown to position for _FORWARD_ Rotation.

"On/Off" Switch controls Motor's input, so if this Switch is Open (Off), the Motor will not run.

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FIGURE #2-2: DIRECTIONAL PSC MOTOR CONNECTIONS - SWITCH CONTROL:
DIRECTION = REVERSE

This Drawing shows the PSC Motor with SPDT Switches used for Forward / Reverse of the Motor.

Switches are thrown to position for _REVERSE_ Rotation.

"On/Off" Switch controls Motor's input, so if this Switch is Open (Off), the Motor will not run.

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FIGURE #3-1a: DIRECTIONAL PSC MOTOR CONNECTIONS - CONTACTOR CONTROLLED:
DIRECTION = N/A (MOTOR AT REST)

*** MOTOR CIRCUITRY ***

This Drawing shows the PSC Motor with Contactors used for Forward / Reverse of the Motor.

Control logic State = "REST" (Motor is Off).

See Fig.# 3-1b below, for Control Schematic

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FIGURE #3-1b: DIRECTIONAL PSC MOTOR CONNECTIONS - CONTACTOR CONTROLLED:
DIRECTION = N/A (MOTOR AT REST)

*** CONTROL CIRCUITRY ***

This Drawing shows the PSC Motor with Contactors used for Forward / Reverse of the Motor.

Control logic State = "REST" (Motor is Off).

See Fig.# 3-1a above, for Control Schematic

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FIGURE #3-2a: DIRECTIONAL PSC MOTOR CONNECTIONS - CONTACTOR CONTROLLED:
DIRECTION = FORWARD

*** MOTOR CIRCUITRY ***

This Drawing shows the PSC Motor with Contactors used for Forward / Reverse of the Motor.

Control logic State = "FORWARD".

See Fig.# 3-2b below, for Control Schematic

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FIGURE #3-2b: DIRECTIONAL PSC MOTOR CONNECTIONS - CONTACTOR CONTROLLED:
DIRECTION = FORWARD

*** CONTROL CIRCUITRY ***

This Drawing shows the PSC Motor with Contactors used for Forward / Reverse of the Motor.

Control logic State = "FORWARD".

See Fig.# 3-2a above, for Control Schematic

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FIGURE #3-1a: DIRECTIONAL PSC MOTOR CONNECTIONS - CONTACTOR CONTROLLED:
DIRECTION = REVERSE

*** MOTOR CIRCUITRY ***

This Drawing shows the PSC Motor with Contactors used for Forward / Reverse of the Motor.

Control logic State = "REVERSE".

See Fig.# 3-3b below, for Control Schematic

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FIGURE #3-3b: DIRECTIONAL PSC MOTOR CONNECTIONS - CONTACTOR CONTROLLED:
DIRECTION = REVERSE

*** CONTROL CIRCUITRY ***

This Drawing shows the PSC Motor with Contactors used for Forward / Reverse of the Motor.

Control logic State = "REVERSE".

See Fig.# 3-3a above, for Control Schematic

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_________________________
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!