C = (P * η / (U₀² * f)) * 100
Where：
C = Capacitor (μF)
P = Power (W)
η = Efficiency (%)
U₀ = Single‑phase voltage (V)
f = Frequency (Hz)
Use this free single-phase motor capacitor calculator to quickly find the right starting capacitor value (in μF) for reliable motor startup. Enter your motor’s power, efficiency, voltage, and frequency to get an accurate recommendation—ideal for DIY repairs, maintenance, or motor retrofitting.
This tool helps you avoid common mistakes like using oversized capacitors (which cause overheating) or wrong types (which fail prematurely). Only CBB-type AC capacitors rated ≥400V should be used.
Use the formula: C (μF) = (100,000 × P × η) / (U₀² × f), where P is the motor’s rated output power in watts, η is efficiency as a decimal (e.g., 0.75 for 75%), U₀ is the single-phase voltage in volts, and f is the supply frequency in Hz. Our calculator automates this—just enter your motor specs to get the correct μF value instantly.
The required capacitor size depends on motor power, voltage, and frequency. For example, a 0.75 kW motor at 230V/50Hz needs about 127 μF. Always use the calculated value—never guess or reuse old capacitors without verification.
No. Only capacitor-start motors require a start capacitor. Permanent Split Capacitor (PSC) and shaded-pole motors use only a run capacitor or no capacitor at all. Check your motor nameplate or wiring diagram to confirm type.
Common signs include: motor won’t start (but runs if spun manually), loud humming noise, bulging or leaking capacitor case, or overheating. You can test it with a multimeter in capacitance mode—if the measured value is more than 10% below rated, replace it.
No. An oversized capacitor causes excessive starting current, which can overheat windings, damage the centrifugal switch, or shorten motor life. Always use the calculated “right μF” value for safe and efficient operation.
Only use non-polarized CBB-type (polypropylene) AC capacitors rated for at least 400V AC. Never use electrolytic, DC, or oil-filled capacitors—they are unsafe and will fail quickly under AC motor conditions.
Only use non-polarized CBB-type (polypropylene) AC capacitors rated for at least 400V AC. Never use electrolytic, DC, or oil-filled capacitors—they are unsafe and will fail quickly under AC motor conditions.
No. An oversized capacitor causes excessive starting current, which can overheat windings, damage the centrifugal switch, or shorten motor life. Always use the calculated “right μF” value for safe and efficient operation.
Common signs include: motor won’t start (but runs if spun manually), loud humming noise, bulging or leaking capacitor case, or overheating. You can test it with a multimeter in capacitance mode—if the measured value is more than 10% below rated, replace it.
No. Only capacitor-start motors require a start capacitor. Permanent Split Capacitor (PSC) and shaded-pole motors use only a run capacitor or no capacitor at all. Check your motor nameplate or wiring diagram to confirm type.
The required capacitor size depends on motor power, voltage, and frequency. For example, a 0.75 kW motor at 230V/50Hz needs about 127 μF. Always use the calculated value—never guess or reuse old capacitors without verification.
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