How to Convert Amperes to Watts

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30-10-2020, 19:10
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Amperes, or amps, measure the flow of electricity as an electrical current, while watts determine the total amount of energy in a circuit. If you know the amount of amps and the voltage in a circuit, you can use those numbers to calculate how many watts is in the circuit, too. Make sure you know whether you’re working on an AC or DC circuit and if the voltage is line to line or line to neutral for the most accurate answer. Although they seem a little complicated, you can get the hang of these equations with patience and practice.

Converting DC Amps

  1. Recognize a DC if the current flows in one direction, not two. DC, or direct current, is an electrical current that only flows in one single direction. On a graph, this would look like a straight line going in one direction.
    • Batteries, like the ones in your electronics, all use DC, not AC.
  2. Identify the volts by multiplying the amps by the resistance. The voltage is the measurement that describes the amount of force needed for the electrical current to flow. If you don’t know the voltage, you can find it by multiplying the amperage by the total amount of resistance in the circuit.
    • You can find the total resistance by adding up each individual resistance measurement inside the circuit.
    • For example, 6 amps x 5 ohms (total resistance) = 30 volts.
    • If you have the circuit in front of you, you can use a voltage meter for a quick and accurate reading.
  3. Multiply the number of amps by the number of volts to calculate watts. Now that you know the amperes and the volts in the current, multiply the 2 numbers together to get the volts. Don’t forget to add the units to your answer.
    • For example, 2 amps x 30 volts = 60 watts.

Converting Single-Phase AC Amps

  1. Identify AC if the electrical current flows back and forth. AC, or alternating current, is an electrical current that flows in both a positive and negative direction. On a graph, it looks like a wavy line, going up and down at an alternating pace.
    • Most home appliances that plug into outlets, like lamps, fans, kitchen utensils, and washing machines, use AC.
    • A single-phase current has only one wire connected to the circuit.
  2. Calculate the power factor, or PF. The power factor is the measurement of how efficiently the current uses its energy, and it’s always a number between 0 and 1. For single-phase circuits, you can find the power factor dividing the true power (how much power the circuit actually puts out) by the apparent power (the combination of true power and reactive power). For example:
    • PF = 119.365 / 169.256 = 0.705.
    • The power factor is always a unitless number.
  3. Multiply the PF times the amps and the voltage to find the watts. To convert your amps to watts, multiply the power factor times the voltage number (the amount of force in the electrical current). Don’t forget to put your units at the end!
    • For example, 2 amps x 30 volts x 0.705 = 42.3 watts.

Converting Three-Phase AC Amps

  1. Figure out if the voltage is line to line or neutral by reading the volts. If the voltage of the equation is 0, that means it is line to neutral. If the voltage of the equation is above 0, it’s line to line. This is important to note, as each one has a different equation to calculate wattage.
    • The voltage is neutral if it’s connected to the earth in some way, or “grounded.”
    • The voltage isn’t neutral if it’s connected from line to line, or not grounded.
  2. Multiply the PF, the voltage, and the amps by √3 for line to line voltage. For line to line voltage, meaning the voltage is above 0, you need to multiply the power factor and the amps by the square root of 3. It may be helpful to do this on a scientific calculator, as the square root of 3 is an irrational number, meaning it can’t be written as a simple fraction. For example:
    • What is power consumption in watts when the power factor is 0.8 and the phase current is 3A and the voltage supply is 110V?
    • Answer: P = √3 × 0.8 × 3A × 110V = 457W.
  3. Use a separate equation for neutral voltage. The main difference in the neutral voltage equation, or voltage that is 0, is that you multiply the amps and voltage by 3, not the square root of 3. The calculation assumes the loads are balanced. The real power P in watts (W) is equal to 3 times the power factor PF times the phase current I in amps (A), times the line to neutral RMS voltage VL-0 in volts (V).
    • In this equation, the watts are always equal to 3 times the power factor and the amps times the volts.
    • For example: 3 x 0.8 x 2 amps x L-0 (neutral volts) = 4.8 watts.

Tips

  • You can calculate watts from amps and volts. You can't convert amps to watts since watts and amps units do not measure the same quantity.
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