Electric Motors
Motor Capacitor Calculator
Estimate motor capacitor size from capacitor current, supply voltage, and frequency. The default values illustrate the workflow; replace them with measurements or ratings from one documented condition.
Inputs for this calculation
Use measurements from one operating condition.
Formula used on this page
This page evaluates C = I ÷ (2πfV). Its variables correspond to Capacitor current, Supply voltage, and Frequency.
For the example shown, required capacitance equals 41.52 µF. Treat that value as a demonstration, not a recommendation.
Estimate motor capacitor size from capacitor current, supply voltage, and frequency. Continue with Motor Poles Frequency Calculator to evaluate nearest even pole count.
How to use the result
The primary answer, Required capacitance, describes only the entered scenario. Compare it with starting demand, running current, torque, efficiency, slip, and thermal loading.
Keep the input set beside the output so another reader can reproduce it. Power Supply Ripple Calculator may be useful for the next related quantity.
Measurements and entries
Separate shaft output power from electrical input power. A source note beside each entry makes the result reproducible.
Values used below a division bar must stay positive. Check every prefix before entry; micro, milli, kilo, and mega are not interchangeable. A separate capacitive reactance result is available from Capacitive Reactance Calculator.
- Capacitor current
- Default example: 3 A. Enter capacitor current in A.
- Supply voltage
- Default example: 230 V. Enter supply voltage in V.
- Frequency
- Default example: 50 Hz. Enter frequency in Hz.
Where this estimate can fail
Motor winding design and manufacturer specifications govern the final capacitor selection.
The simple equation may need adjustment for load inertia, acceleration profile, harmonics, reduced-speed cooling, and mechanical loss. Use measurements, manufacturer data, or another calculation for effects that can change the decision.
Separate shaft output power from electrical input power.
Documenting the calculation
Document capacitor current, supply voltage, and frequency with required capacitance. Keep enough context to reproduce the result later.
Carry required capacitance unchanged when passing it to the next worksheet. Apply standard sizes only after all checks are complete.
Before relying on the answer
Which source values should I use for Required capacitance?
Choose entries that describe the same case. Record supply arrangement, speed, duty cycle, enclosure, and winding temperature.
What should I verify beyond the displayed inputs?
Motor winding design and manufacturer specifications govern the final capacitor selection. Also consider starting method, service factor, enclosure, and thermal duty.
Why might a second instrument give another answer?
Recheck units and operating state before investigating voltage imbalance, drive waveform, transient torque, and bearing load.