wendel,
Brief answers, to your question regarding the PSC Motor:
On a typical HVAC 3 speed PSC motor, are speeds determined by individual windings - with only the neutral being common to all; or are there taps off one large winding?
The PSC (Permanent Split Capacitor) type Single Phase Induction Motor achieves a reduced speed, by reducing the Voltage observed at the Motor's Main and Auxiliary Windings.
The PSC Motor uses an intregal Autotransformer for speed control selections, rather than including multiple Poles for altering the Frequency - as would be done with other types of Squirrel-Cage, "Short-Circuited Rotor" type Induction Motors.
The Autotransformer is wound to the same Stator Assembly, as the Main and Auxiliary Windings are wound to.
The Autotransformer is connected to the Main and Auxiliary Motor Windings' "common" connection point on one side, and brings in one side of the 2 wire circuit through one of the tapped speed selection leads (or directly to the Motor Windings for full speed).
The Autotransformer is tapped at various points along the Winding's "Build", relative to the number of turns required for a certain Voltage.
These taps are connected to the AC input through a selector switch, which allows only one lead to be connected at a time (or no leads connected to turn the Motor off).
Example Speed Selections For A "3-Speed PSC Motor":
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[*] The "Full / High Speed" input selection tap is made between the "_END_" of the Autotransformer Winding, and the "_BEGINNING_" of the Main Motor Winding.
This selection point bypasses the speed control Autotransformer, and runs the Motor at Designed RPMs - applying full Voltage to the Motor Windings,
[*] The "Medium Speed" input selection tap is made on the Autotransformer's Winding - at apx. 50% of the Winding's length, which reduces the Voltage at the Motor's Windings by apx. 20% (+ or -),
[*] The "Low Speed" input selection tap is made at the "_BEGINNING_" of the Autotransformer's Winding - the opposite end from which the Motor Winding leads are connected. This reduces the Voltage at the Motor's Windings by apx. 40% (+ or -).
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The remaining Motor Windings' "Ends" are connected directly to the "2nd Conductor" of the 2 wire AC circuit.
Typically, on Circuits using a Grounded Conductor for "L-N" 2-Wire AC Circuitry, this "2nd Conductor" is the System's Grounded Neutral Conductor.
For "L-L" 2-Wire AC Branch Circuitry, no Grounded Conductor is utilized on the Circuit, so that "2nd Conductor" is an Ungrounded Conductor.
Since there is no relative "Polarity" involved with a 2-Wire AC Circuit, it does not matter which Conductor is terminated to any certain Motor Input Lead. Direction of Motor rotation depends on "Which Side Of The Main Winding Gets Reduced By The Auxiliary Winding", not by the 2-Wire AC input Circuitry.
(i.e. The input 2-wire circuit's terminations to the Motor's input may be reversed, with no change in direction for the Motor's rotation).
Attached are a few Schematics, which describe some Single Phase Induction Motors.
Feel free to comment or ask additional questions, regarding this topic &/or the Schematics.
Scott35
Images Below...........................
Fig. 1.1: PSC Induction Motor Circuit Diagram-C.C.W Rotation (normal rotation)
"L1" + "L2" = Motor Input Line Leads,
"1" = Main Winding,
"2" = Auxiliary Winding,
"3" = Capacitor (always in circuit),
"4" = Squirrel Cage rotor,
"5" = AC Line Input,
"6" = Intregally Wound AutoTransformer (for speed control).
Fig. 1.2: PSC Induction Motor Circuit Diagram-C.W Rotation (reversed rotation)
"L1" + "L2" = Motor Input Line Leads,
"1" = Main Winding,
"2" = Auxiliary Winding,
"3" = Capacitor (always in circuit),
"4" = Squirrel Cage rotor,
"5" = AC Line Input,
"6" = Intregally Wound AutoTransformer (for speed control).
Fig. 1.3: Speed Control Switch Detail
*Note: The AutoTransformer shown in Fig. 1.1 and 1.2 is wound onto the same "core"
as the Motor's Stator windings. Additional taps may be inserted for increased levels of speed control.
The "100%" tap is both the end of the AutoTransformer and the Motor's Lead.
Connecting directly to this lead will result in full Motor speed.
Fig. 1.1: Capacitor Start Induction Motor Circuit Diagram-C.C.W Rotation (normal rotation)
"L1" + "L2" = Motor Input Line Leads,
"1" = Run (Main) Winding,
"2" = Start (Auxiliary) Winding,
"3" = Centrifugal Start Switch,
"4" = Squirrel Cage rotor,
"5" = Start Capacitor,
"6" = AC Line Input.
Fig. 1.1: Capacitor Start/Run Induction Motor Circuit Diagram-C.C.W Rotation (normal rotation)
"L1" + "L2" = Motor Input Line Leads,
"1" = Run (Main) Winding,
"2" = Start (Auxiliary) Winding,
"3" = Centrifugal Start Switch (shown in the "Run" position, connecting the "Run" Capacitor),
"4" = Squirrel Cage rotor,
"5" = "Run" Capacitor,
"6" = "Start" Capacitor,
"7" = AC Line Input.
Fig. 3.1: Shaded Pole Induction Motor Circuit Diagram
"L1" + "L2" = Motor Input Line Leads,
"1" = Run (Main) Winding,
"2" = Shading Coil (Auxiliary Winding),
"3" = Short Circuiting Connection,
"4" = Squirrel Cage rotor,
"5" = AC Line Input.
Fig. 1.1: Resistance Start Induction Motor Circuit Diagram-C.C.W Rotation (normal rotation)
"L1" + "L2" = Motor Input Line Leads,
"1" = Run (Main) Winding,
"2" = Start (Auxiliary) Winding,
"3" = Centrifugal Start Switch,
"4" = Squirrel Cage rotor,
"5" = AC Line Input.
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