Ceiling Fan & Pump Motor Capacitor Calculator: PSC Run µF

For the reduced two-phase equivalent circuit at one operating point, take RMS supply V as the phase reference and use positive inductive reactances. The branches are $Z_m=R_m+jX_m$ and $Z_a=R_a+j(X_a-X_C)$, with $X_C=1/(2\pi fC)$. Then $I_m=V/Z_m$, $I_a=V/Z_a$, $I_L=I_m+I_a$, and $V_C=|I_a|X_C$.

Setting $\arg I_a-\arg I_m=90^\circ$ gives

This is a phase-quadrature target, not automatically a balanced-motor design. With $a=(N_a k_{wa})/(N_m k_{wm})$, balance also requires $a|I_a|/|I_m|=1$. At the phase target this ratio reduces to $aX_m/R_a$; equivalently, $a=R_a/X_m$. If it differs from one, no capacitor alone achieves both requirements in this fixed-impedance model.

The equations above are derived here from branch KVL and phasor quadrature. University of Utah ECE 3600 notes, attached s1 pp. 2–4, give the fixed-slip approximation and independent run/start worked examples. NPTEL Electrical Machines II lectures 69–73 provide the broader single-phase starting and phase-splitting context.

The auxiliary copper-loss comparison is $(|I_a|/|I_{a,90}|)^2$, assuming unchanged copper resistance. Equivalent input resistances include rotor/load effects and are not treated as pure copper resistance. The tool does not calculate temperature.

Label mode copies the specified capacitance. Fan-example mode reads a sourced, editable model row. Winding mode uses the analytical phase target. None overrides a manufacturer's approved run-capacitor specification.

Sinusoidal single-phase supply; ideal lossless series capacitor; windings displaced by 90 electrical degrees. Winding impedances are effective terminal values for the same fixed speed, load and frequency, before capacitor addition. Treating them as independent constant branches is a local approximation; mutual/sequence effects and changes of slip are not re-solved when capacitance changes.

The winding defaults (500+j600 Ω main, 1000+j440 Ω auxiliary, effective turns ratio 5/3) are an authored illustrative example, not measured fan data. They are not used to select a replacement in nameplate or fan-example mode. In those modes the phasors show an idealised 90° concept without numerical motor-current claims. In nameplate and fan-example modes, every winding calculation is explicitly labelled as an unrelated repair-mode teaching example. The calculation details identify the exact hidden illustrative impedances beside this group. Those numbers do not predict the repaired motor. In winding-data mode, the same equations use the visible winding inputs.

The Ventair size presets are specific published model examples, not population averages for Indian or Pakistani ceiling fans. The user can edit a preset or enter an exact marking. A matching AC voltage rating assumes the original part was correct; this comparison is not a complete capacitor qualification.

Use for conventional permanent-split-capacitor fan and pump motors with the run capacitor permanently in series with the auxiliary winding. Not for BLDC/electronically commutated fans, three-phase conversion, multi-section speed-control capacitor networks, or short-duty start-capacitor sizing. Pump and compressor start/run topology must be identified from the manufacturer's circuit.

Winding-model predictions are local to the entered operating point. Do not use locked-rotor impedances as running data, or change frequency while keeping reactances from another frequency. The start-condition reference cases validate the same phasor algebra at standstill; they are not run-capacitor recommendations.

No shaft-speed, torque-speed, saturation, harmonic, thermal, transient or service-life prediction is made. Capacitor RMS voltage may exceed the mains. Match the original µF and AC rating; any alternative rating requires manufacturer approval with suitable continuous duty, tolerance and temperature class. The ampere-turn warning identifies departures from mathematical equality within 10⁻⁶; it is not a permissible design tolerance.

Installation, testing and replacement belong to a qualified person. Isolate the supply, prevent reconnection and verify safe capacitor discharge before handling.