Calculating the Ac three phase from Volts to Watts. P (W) = √3 x PF x I (A) x V L-L (V), which means that the real power in watts is calculated by multiplying the square root of three by the power factor times the phase current in amps. The result is then multiplied by the voltage RMS in volts.
Determine the watts in a power source. You will need to know the amps and the volts in the power source. To determine the wattage, use a simple multiplication formula. The ampere (or amps) is the amount of electricity used. Voltage measures the force or pressure of the electricity.
- The number of watts is equal to amps multiplied by volts. That's it! In other words, watt=amp X volt. Sometimes you will see this formula written as W=A X V. [1]
- For example, if the current is 3 amps (3A) and the voltage is 110V, you multiply 3 by 110, to get 330W (watts). The formula is P=3A X 110V = 330 W (with P standing for power).
- This is why watts are sometimes called volt-amps. Circuit breakers usually have the amps written on their handles. This is the maximum amperage that circuit can take before the circuit breaker trips. You can also determine both volts and amps by looking on the labels or in the operating manuals. You can look up common figures for standard appliances (most small appliances and lighting fixtures in homes require circuits that range from 15-20 amps and larger ones are 20 to 60. However, most counter top household appliances are rated for 120 volts and operated with 12 or less amps. Larger appliances like ranges and clothes dryers require more power and are connected to circuits that are wired to 240 volt power and may draw 20 to 40 amps depending on a number of factors. Household wiring is usually 120 or 240 volts in North America.
Some pylons near a power transform station at sunrise. More voltage in an electrical system makes more current flow. dowell/Getty Images
So much of our daily lives runs on electricity, yet most of us don't know the difference between a 60-watt and 75-watt light bulb, or how voltage from the wall socket supplies enough juice to run both a small desk lamp and a powerful microwave.
The three most basic units in electricity are voltage (V), current (I, uppercase 'i') and resistance (R). Voltage is measured in volts, current is measured in amps and resistance is measured in ohms.
A neat analogy to help understand these terms is a system of plumbing pipes. The voltage is equivalent to the water pressure, the current is equivalent to the flow rate, and the resistance is like the pipe size.
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There is a basic equation in electrical engineering that states how the three terms relate. It says that the current is equal to the voltage divided by the resistance or I = V/R. This is known as Ohm's law.
Let's see how this relation applies to the plumbing system. Let's say you have a tank of pressurized water connected to a hose that you are using to water the garden.
What happens if you increase the pressure in the tank? You probably can guess that this makes more water come out of the hose. The same is true of an electrical system: Increasing the voltage will make more current flow.
Let's say you increase the diameter of the hose and all of the fittings to the tank. You probably guessed that this also makes more water come out of the hose. This is like decreasing the resistance in an electrical system, which increases the current flow.
Electrical power is measured in watts. In an electrical system power (P) is equal to the voltage multiplied by the current.
The water analogy still applies. Take a hose and point it at a waterwheel like the ones that were used to turn grinding stones in watermills. You can increase the power generated by the waterwheel in two ways. If you increase the pressure of the water coming out of the hose, it hits the waterwheel with a lot more force and the wheel turns faster, generating more power. If you increase the flow rate, the waterwheel turns faster because of the weight of the extra water hitting it.
On the next page, we'll talk more about electrical efficiency.