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NORA Oilheat Technicians Manual

Start Switch Main Winding Older Burner Motor PSC Motor PSC (Permanent Split Capacitor) motors Most new oilburners feature PSC motors. A PSC motor uses a capacitor (a device that stores and releases an electrical charge) in one of the windings to increase the current lag between the two windings. Unlike conventional capacitor start motors, PSC motors have no centrifugal starting switch and the second winding is permanently connected to the power source. Both Table 10-1: Heating system motor testing chart (courtesy Beckett Corp.) Chapter 10 Motors Figure 10-11: Motor circuits PSC motor Test Parameter Split Phase PSC Comments Average starting current 15-25 Amps 7 Amps PSC has a decreased starting current, (locked rotor current) which extends primary control relay life. Average running current 2.0 - 2.4 Amps 1.5 Amps PSC draws an average 30% less current. Approximate starting torque 55 - 70 oz-in 49 oz-in General mini pump starting torque requirement: 13 - 20 oz-in. 1 Average electrical power 200 Watts 170 Watts PSC draws an average 15% less power. Efficiency 40 - 50% 60 - 65% Efficiency = output power (mechanical) divided by input power (electrical) AFG full load speed 3375 - 3450 rpm 2 3440 - 3460 2 PSC: Similar or increased output power. 1 Most standard oil pumps (for instance, the Suntec A or B models) do not require as much power or starting torque as the larger pumps (for instance, Suntec J and H models), which often are provided with a 1/5 hp motor. 2 Rule of thumb: Air flow (cfm) is proportional to motor speed, and static pressure varies with the motor speed squared (if the speed increases by 2%, the pressure increases by 4%). Chapter 10—Motors 10-9 Run (Main) Winding Start Winding L1 L2 L1 L2 Auxiliary Winding Capacitor the capacitor (auxiliary) winding, and the main winding remain in the circuit the entire time the motor is running—hence the name “permanent.” PSC Motors perform with better efficiency, offer equal or increased power output and lower starting and running current than conventional split phase motors. See Figures 10-11 and Table 10-1.


NORA Oilheat Technicians Manual
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