How do I calculate motor capacitor size?

For a run capacitor: C ≈ P/(2π×f×V²×η×cosφ) × 10⁶ μF. A rough rule of thumb is 30-50 μF per HP for run capacitors and 100-150 μF per HP for start capacitors.

What is the difference between start and run capacitors?

Start capacitors are electrolytic, high-value (70-400 μF), used only during startup then disconnected by a centrifugal switch. Run capacitors are film type, lower value (5-60 μF), and remain in circuit continuously.

What happens if the capacitor is too small?

Too small: motor may not start (low starting torque), may overheat, reduced efficiency. Too large: excessive current in auxiliary winding, overheating, possible winding damage.

Can I use a higher voltage capacitor?

Yes, using a capacitor with a higher voltage rating is safe. However, never use a lower voltage rating than required — typically 1.5× the supply voltage for safety margin.

What are PSC and CSIR motors?

PSC (Permanent Split Capacitor) uses a run capacitor only — simple but lower starting torque. CSIR (Capacitor Start Induction Run) adds a start capacitor with centrifugal switch for higher starting torque, typical for compressors and pumps.

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馬達電容計算器

計算單相馬達的啟動與運轉電容值。C = I / (2πfV)。估算基於馬達功率、電壓與頻率。

啟動電容運轉電容單相

結果

運轉電容（估算）

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啟動電容（估算）

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馬達電流

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電容最低電壓額定值

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電容公式

啟動電容通常為運轉電容值的 3–5 倍。運轉電容使用薄膜介電質；啟動電容使用電解質。

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馬達電容計算器 — C = I/(2πfV) | Vibromera

結果

電容公式

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