It’s quite easy to convert kW to amps and amps to kW in a simple 1-phase DC circuit (compared to a 3-phase power calculation). That requires only the basic Ohm’s law; you can simply use our kW to amps calculator here for conversion.
In a 3-phase AC circuit (usually a 3-phase motor), converting amps to kW and kW to amps is not all that easy. To simplify the whole thing, we have created 2 three-phase power calculators:
- First 3-phase power calculator converts kW to amps. For this, we use the 3-phase power formula with the 1.732 factor and power factor (we’ll cover the formula as well). You can jump to 3-phase kW to amps calculator here.
- Second 3-phase power calculator converts amps to kW in much the same way. We apply the classic 3-phase motor current calculation formula. You can jump to 3-phase amps to kW formula and calculator here.
To get an idea of how these calculators work, here is the screenshot of the 3-phase power calculator:
Before we cover the basics, let’s do a quick example to illustrate how calculating power on a 1-phase vs 3-phase circuit works.
Example: Let’s say we have a 6 kW air conditioner on a 120V circuit. Here’s how many amps does it draw:
- On a 1-phase circuit, 6 kW draws 50 amps.
- On a 3-phase circuit (with a 1.0 power factor), the 3-phase power calculator shows that the same 6 kW appliance draws 28.87 amps.
- On a 3-phase circuit (with a 0.6 power factor), the 3-phase power calculator shows that the same 6 kW appliance draws 48.11 amps.
To see why we get different amperage on a 3-phase circuit, let’s first check how these amps are calculated using the 3-phase power formula:
3-Phase Power Formula
Here’s the simple formula we use to calculate power on a 1-phase DC and AC circuit:
P (kW) = I (Amps) × V (Volts) ÷ 1,000
Basically, we just multiply amp by volts. The ‘1,000’ factor is there to convert from W to kW; we want the resulting power to be in kilowatts. 1 kW = 1,000W.
Compared to this, the 3-phase power formula is a bit more complex. Here’s the 3-phase power equation:
P (kW) = (I (Amps) × V (Volts) × PF × 1.732) ÷ 1,000
As we can see, the electrical power in the 3-phase AC circuit depends on:
- I (Amps): Electrical current, measured in amps. The more amps we have, the more power we have in a three-phase circuit.
- V (Volts): Electrical potential, measured in volts. The more volts we have, the more power we have in a three-phase circuit.
- PF: Power factor, it’s a number between -1 and 1 (0 and 1 in practice). Power factor is defined as a ratio between real power and apparent power. If current and voltage are in phase, the power factor is 1. In the 3-phase circuit, current and voltage are not in phase; thus the power factor will be anywhere between 0 and 1. This accounts for the real/apparent power ratio and is sometimes expressed as RMS current. The higher the PF, the more kW a 3-phase circuit has.
- 1.732 factor: This is a constant in the 3-phase power calculation. It comes from the derivation of this equation. To be exact, we get a square root of 3 (√3).
- 1,000 factor: This is another constant. It converts watts into kilowatts because we usually prefer to deal with kW instead of W.
Because we need to use the power factor to calculate the kW from amps, this formula is also known as the ‘3-phase power factor formula’.
We can use this equation to design the 1st calculator: 3-phase power calculator (check below).
Note: Later on, we will also see how we can use the 3-phase current formula to design a 3-phase motor amps calculator. That one converts kW to amps in 3-phase circuits, very important in electric motor design.
3-Phase Power Calculator: Amps To kW (1st Calculator)
You can freely use this calculator to convert amps to kW in a 3-phase circuit. You need to input the amps, voltage, and the power factor (it’s between 0 and 1, specific for each circuit):
As you can see, the more amps and volts you have, the more powerful 3-phase electric motor you have. Quite similarly, a higher power factor is proportional to higher power output.
You can use this example to see how the 3-phase power calculator works: A 100 amps motor on a 240V 3-phase circuit with a 0.9 power factor produces 37.41 kW of electrical power. Insert these 3 quantities in the calculator, and you should get the same result.
Now for the 3-phase motor current calculation formula:
3-Phase Current Formula
As we have seen, this 3-phase power formula calculates how many kW of electric power will a motor have given its current:
P (kW) = (I (Amps) × V (Volts) × PF × 1.732) ÷ 1,000
To figure out how many amps does a motor with certain kW power have, we have to rearrange this equation a bit. We get the 3-phase current formula like this:
I (Amps) = P (kW) × 1,000 ÷ (V (Volts) × PF × 1.732)
Using this power formula, we can, for example, do a 3-phase motor kW to amps calculation. Do note that if a 3-phase motor with lower voltage and lower power factor will draw more amps to produce the same power output.
Here is the calculator based on the 3-phase current formula:
3-Phase Motor Amps Calculation: kW To Amps (2nd Calculator)
To calculate the amps from kW, you need to input the kW, voltage, and power factor of a 3-phase motor. The calculator will dynamically calculate the current (amps) based on your inputs:
You can use this example to check if you’re correctly using the 3-phase current calculator: Let’s say we have a 200 kW motor on a 480V 3-phase circuit with a 0.8 power factor. Such a motor has a 300.70 amp draw. You can insert these numbers into the calculator and see if you get the correct result.
All in all, we hope these calculators help you determine the power and current specifications of electric motors. If you have any questions, you can use the comments below and we’ll try to help you out.