What This Calculator Does
Single-phase AC induction motors often need a run capacitor to shift the phase of current in a secondary winding, improving starting torque and running efficiency. This calculator gives a quick estimate of the capacitor size (in microfarads) based on the motor’s full load current and supply voltage, using a widely used rule-of-thumb sizing formula.
The Formula
The estimate uses C (µF) = (2650 × I ÷ V) × (60 ÷ f), where I is the motor’s full load current in amps, V is the supply voltage, and f is the supply frequency in Hz. The 2650 constant is a commonly published rule-of-thumb factor for 60Hz single-phase motor run capacitor selection, scaled here for 50Hz systems since capacitive reactance is inversely proportional to frequency.
- Rule of thumb only: this gives a reasonable starting estimate, not an exact engineering calculation.
- Always check the motor nameplate or manufacturer documentation for the recommended capacitor value and voltage rating first, since actual capacitor requirements vary by motor design.
This calculator is for general planning and educational purposes only; consult the motor manufacturer’s specifications or a qualified electrician before selecting or installing a capacitor on real equipment.