ボルトから アンペア 計算機
電圧と電流の関係を理解しましょう。特定の電圧と電力負荷から何アンペアになるかを正確に計算します。
電流分析
電圧 + 電力 → アンペア
回路に流れる結果としての電流。
変換式
回路が直流か交流かによって、また交流システムの場合は力率によって、電流の計算方法が変わります。
直流システム
I = (kW × 1000) ÷ V 直流には位相角がありません。電流は単純に電力を電圧で割った値です。
単相AC
I = (kW × 1000) ÷ (V × PF) 力率は交流回路の有効電力を低下させます。力率0.9とは、実際の電力が示すよりも10%多い電流が流れることを意味します。
三相AC
I = (kW × 1000) ÷ (√3 × V × PF) 三相電力は3本の導体に分配されます。√3（1.732）という係数は、それらの間の位相関係を考慮したものです。
How to Convert Volts to Amps
Converting voltage to current requires knowing the power being consumed or the resistance in the circuit. When you know power (in kW or W), Ohm's Law and the power formula give you current directly. This calculation is essential for sizing circuit breakers, fuses, wire gauges, and selecting protective equipment.
Why Voltage and Current Move in Opposite Directions
For a fixed load, doubling the voltage halves the current. This inverse relationship is why high-voltage transmission lines carry massive power across long distances using thin cables — lower current means less resistive heating and power loss in the wire.
Practical Applications
- Circuit Breaker Sizing: A 2kW heater on 240V single-phase draws about 8.7A at unity PF — you'd protect it with a 10A or 15A breaker.
- Wire Gauge Selection: Higher current requires thicker wire to stay within safe temperature limits. Use the NEC or IEC ampacity tables after calculating current.
- Fuse Selection: Fuses must be rated at 125% of continuous load current. Calculate first, then select the fuse size.
- Motor Nameplate Verification: Cross-check the listed FLA (Full Load Amps) against the calculated current from rated HP and voltage.
Step-by-Step Conversion
- Note the Power: Find the kW or watt rating on the equipment label.
- Read the Voltage: Confirm the system voltage — check the supply panel or equipment nameplate.
- Identify AC or DC: DC circuits use the simple formula; AC circuits need the power factor applied.
- Calculate and Size Up: Always round up to the next standard breaker or fuse size after calculating.