To calculate the power (watts) absorbed by an electronic device just solve a simple equation. The only information necessary for the calculation is the number of amperes (A) and the number of volts required for the operation of the device in question. Understand that knowing the watts consumed by a particular electrical appliance is very important, because it allows you to save precious energy and therefore money.
Steps
Part 1 of 3: Mathematically Calculate Absorbed Watts
Step 1. Determine the watts delivered by the power source
To do this, you need to know the number of amperes of volts supplied to the apparatus in question. To calculate the delivered power, a simple multiplication must be performed.
- The number of watts equals the number of amps multiplied by the number of volts. Simple right? In other words, the equation to use is the following: P = I x V (where P is the power expressed in watts, V is the voltage expressed in volts and I is the current expressed in amperes).
- For example, if the current is 3 A and the voltage is 110 V, applying the formula in question we will obtain that the power is 330 W. The formula is the following P = 3 A * 110 V = 330 W.
- This is why watts are sometimes referred to as volt-amperes.
Step 2. Similarly you can determine amps or volts
To do this you will have to use the inverse formula obtainable from the starting equation. For example, let's say we have a 24-40 AC power supply; this means that it is able to supply a power of 40 watts with a voltage of 24 volts.
- This power supply is capable of delivering a current of 1, 6 A. The formula used for the calculation is the following: 40 = I x 24. Therefore, solving the equation based on I, we obtain I = 40/24 that is 1, 6 A.
- Here is another example you may need to use this formula for. Let's say you want to know the power absorbed by a ceiling fan. As an initial figure you are aware of the number of amps required for its operation. At this point you need to find out the number of volts that must be supplied to the device (to do this you can call the manufacturer or perform an online search). As a last step, multiply the two numbers together to get an estimate of the power required for normal fan operation.
Step 3. Determine the power drawn by a resistor
To do this, you need to know the voltage (V) applied to the component and the current (I). The equation that links these three quantities is known as Ohm's Law.
- The equation underlying this law is expressed as follows: P = V * I.. In some formulas the power, instead of being indicated with the letter P, could be indicated with the letter W.
- The formula becomes much more complex if applied in the real field, where the absorbed power varies according to time. In this case, time must also be taken into account to calculate the average power. This is a very complex calculation, therefore, in the case of this type of measurement, it is always better to use a special instrument called a wattmeter.
Part 2 of 3: Using an Automatic Calculation Tool
Step 1. Find an online calculator
On the web you can find numerous resources that can be used to calculate the power consumed by a particular device. At the base of these calculators is always the Ohm's Law equation, but with the advantage that they will do the calculations for you.
- Normally these electronic calculators require you to supply the voltage (in volts) and the current (in amperes), then the "Calculate" or "Calculate" button must be pressed to obtain the number of watts.
- Remember that these tools are not always accurate as each appliance or device needs a slightly different power voltage.
- Some online tools provide the number of watts needed based on the type of device selected, such as a television or desktop computer. Some websites also provide a graphical representation of the power consumed by different devices, from refrigerators to portable stereo radios.
Step 2. Check the specifications of your appliance
By reading the label printed directly on the device you will be able to know precisely the power absorbed.
- This label is usually found on the back of the appliance. You will most likely find listed the volts, amps, and watts needed by the device for its normal operation. If this information is not shown on the appliance, always refer to the instruction manual provided by the manufacturer.
- By connecting a wattmeter to the appliance you will immediately discover the exact amount of power needed for its operation. The number of watts drawn by a given device may vary based on the operating settings. For example, a radio will draw more power if you increase its volume.
Part 3 of 3: Additional Potency Information
Step 1. Understand why power matters
Power expressed in watts indicates how energy is generated or used. Many electricity companies base their bills exactly on the number of watts they consume. Basically, power expresses the amount of energy used by a device or household appliance.
- The number of rated watts indicates the amount of power needed to keep an appliance or device running. For example, a refrigerator normally requires 500 watts for its normal operation.
- The peak power indicates the maximum amount of watt absorbed by the device, which generally corresponds to that required at start-up, i.e. when the motor or compressor is turned on. For example, a normal refrigerator might have a peak power of 2000 watts when the compressor is started.
Step 2. Use energy efficiently
Watt is the unit of measurement of power (electrical, mechanical or thermal). The reason why watts are so important is that, once you understand what they mean, they allow you to use energy efficiently.
- Decrease the number of watts consumed. In this way you will increase energy efficiency and decrease costs. For example, let's say you bought a 100-watt and a 23-watt light bulb. If the 100-watt light bulb were the cheapest, you might think it's the best purchase option available to you. However, over time, the 23 watt bulb will save you more money.
- To determine the difference in power, do a simple subtraction. In our example we get a difference of 77 watts (100-23). Electricity companies normally charge their bills based on the kilowatts consumed. To calculate the number of kilowatts, simply divide the number of watts by 1000 and then multiply the number of kilowatts by the hours of use; as a result we will get kilowatt hours (kWh). In order to calculate your savings, multiply the kilowatt hours by the rate applied by the company that supplies you with electricity. The final result will be the annual cost of the energy consumed.
- For example, let's say we have 10 light bulbs of 100 watts each. The overall power will be 10 x 100 = 1000 watts. To get the kilowatts we divide the result by 1000 to get 1 kWh. Let's assume that we use all the bulbs for 2000 hours a year; we will then get 1 kW x 2000 hours = 2000 kWh. If the company that provides the electricity applied a tariff of 10 cents per kWh, we would get 2000 kWh x 0, 10 = 200 €. This is the cost you will have to incur to use the bulbs in question each year.
Advice
It is important to take into account a small amount of additional power for each device that you will connect to the circuit or inverter. Many electronic devices, in fact, absorb energy even when they are turned off, in particular those that have the classic LED stand-by light
Warnings
- If you demand too much power from the inverter you risk burning it.
- Too many devices connected to the output of an inverter could be underpowered. This could damage them or cause them to shut down.
- The values calculated in this article are approximate; if you need to measure real values accurately you have to use a wattmeter.
