Introduction to PSC Motors:
Commonly used in furnace blowers, condenser fans, older compressors, and circulator pumps.
Features: Low starting torque, medium efficiency, and low to medium cost.
Wiring of PSC Motors:
Basic wiring involves line voltage to common and run terminals.
The run capacitor is wired in series with the start winding, limiting current and pushing it out of phase.
Typically, the capacitor is pre-wired by the manufacturer.
Motor Speed and Pole Count:
Motor speed is determined by the number of poles (windings).
Formula: Speed = 7200 / number of poles.
Example: A 2-pole motor runs at approximately 3450 RPM, while a 4-pole motor runs at around 1750 RPM due to slippage.
Multi-Speed PSC Motors:
Run winding is segmented with multiple taps, allowing for different resistance levels and speeds.
High speed: Line power to RH terminal.
Medium speed: Line power to RM terminal (increased resistance, lower speed).
Low speed: Line power to RL terminal (highest resistance, lowest speed).
Three-Speed PSC Motor Wiring:
Standard color codes: Black (high speed), Blue (medium speed), Red (low speed).
Additional colors (Yellow/Orange) may indicate medium-low or medium-high speeds.
Capacitor wiring is typically done by the manufacturer.
Effect of Speed on Airflow:
Blower speed affects CFM (Cubic Feet per Minute) based on external static pressure.
High speed at 0.5 inches of water column: 1230 CFM.
Medium speed: 1119 CFM.
Low speed: 915 CFM.
Lower static pressure results in higher CFM.
PSC Motor Components:
Includes run capacitor leads, common wire, and speed taps (high, medium, low).
Additional speed options may be available, usually color-coded (e.g., orange/yellow).
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