kWからアンペア計算機 ロゴ
kWからアンペア計算機
🛠️ モーター出力監査

アンペアから 馬力に 計算機

ラインから引き込む電流に基づいて、モーターの出力を馬力で逆算します。現場での機器仕様確認に最適です。

モーター出力監査

電流 → 出力馬力

小数点以下
2
モーター出力
—
HP

電気入力に基づく軸馬力です。

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変換式

モーター出力馬力は電気入力から計算されます。効率と力率が、どれだけのエネルギーが機械的仕事になるかを決定します。

直流モーター
HP = (I × V × Eff) ÷ 746

電気入力電力（I×V）に効率を掛けると出力ワットが得られ、それを746で割ると馬力になります。

単相ACモーター群
HP = (I × V × Eff × PF) ÷ 746

交流モーターには力率が必要です。実効電力部分（V×I×PF）のみが機械的出力に変換されます。

三相ACモーター群
HP = (√3 × I × V × Eff × PF) ÷ 746

√3係数は3つの相にわたる電力分配を考慮したものです。三相モーターは単相よりもアンペアあたり多くの電力を供給します。

How to Convert Amps to Horsepower

Converting amps to horsepower lets you determine a motor's mechanical output from its electrical input measurements. This is useful when the motor nameplate is damaged or missing, when verifying motor performance, or when comparing measured current draw to the rated HP. The key insight: not all electrical input becomes mechanical output — efficiency and power factor dictate how much is lost as heat.

Understanding Motor Efficiency

Motor efficiency is the ratio of mechanical output power to electrical input power. A 5 HP motor drawing 15A at 240V and 0.85 PF consumes about 3,060W of real input power. At 90% efficiency, it delivers 2,754W (≈ 3.69 HP) of mechanical output. The rest becomes heat in the windings. Premium-efficiency motors minimize this loss.

When to Use This Calculation

  • Verifying Motor Output: Measure FLA with a clamp meter and calculate HP to confirm the motor is delivering its rated output.
  • Troubleshooting Overloads: If the calculated HP is significantly below rated, the motor may be worn, undersized, or operating with a degraded power factor.
  • Pump and Fan Selection: When replacing driven equipment, knowing actual HP output (not just nameplate) prevents under-sizing the new load.
  • Energy Audits: Calculate actual HP output versus nameplate rating to identify inefficient motors worth replacing with premium-efficiency units.

Step-by-Step Conversion

  1. Measure or Find the Current: Use a clamp meter for measured FLA, or use the nameplate value.
  2. Note the Supply Voltage: Use line-to-line voltage for three-phase; line-to-neutral for single-phase.
  3. Multiply by Efficiency: Motor efficiency in decimal form (85% = 0.85).
  4. Multiply by Power Factor (AC): Typical induction motors run 0.80–0.92 PF at full load.
  5. Divide by 746: Convert watts to horsepower using the 746 W/HP constant.