Free Engineering Tool
Motor Capacitor Calculator
Calculate start and run capacitor values for single-phase motors. C = I / (2πfV). Estimates based on motor power, voltage, and frequency.
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Capacitor Formula
Start capacitors are typically 3–5× the run capacitor value. Run capacitors use film dielectric; start capacitors use electrolytic.
Run cap ≈ 30–50 μF/HP. Start cap ≈ 100–150 μF/HP. More precisely: C = I/(2πfV) for the auxiliary winding current.
Start: electrolytic, 70–400 μF, momentary use with centrifugal switch. Run: film, 5–60 μF, continuous duty.
Motor may not start, overheat, or have reduced efficiency. Too large causes excess auxiliary winding current and overheating.
Yes, higher voltage rating is safe. Never go lower. Use ≥1.5× supply voltage for safety margin.
PSC: run cap only, simple, lower starting torque. CSIR: start cap + centrifugal switch, higher starting torque for compressors/pumps.
The procedures described on this page were developed and field-tested by the Vibromera team using the Balanset-1A, a portable dual-channel balancer and vibration analyzer for on-site rotor balancing.
Professional instruments. Used in 50+ countries.
Nikolai Shelkovenko
Nikolai Shelkovenko is a vibration analysis engineer and the founder and CEO of Vibromera. For more than 15 years he has balanced rotating equipment in the field rather than on a test bench: mulchers, industrial fans, crushers, centrifuges, shafts and spindles. That work is what the Balanset instruments grew out of — they were designed as a tool a specialist can carry to the machine and use alone, on site, not as laboratory equipment. Vibromera was founded in 2017 and has been based in Porto, Portugal, since 2023. Development, assembly and support of the Balanset line all happen here. The flagship instrument is the Balanset-1A, a portable analyser for single- and two-plane balancing and for vibration diagnostics. Nikolai is personally involved in customer support, in working through difficult balancing cases and in the development of the software. He works with customers worldwide, in any language.
