While there is no direct way to convert watts (W) to amperes (A), it is possible to calculate the intensity of the current flowing in an electrical circuit using the physical relationships that tie electrical current, power, and voltage. These bonds vary according to the type of power supply used: alternating (AC) or direct (DC) voltage. However, within specific circuits, these relationships will always be the same. If you are working on an electrical circuit with a constant voltage, it is very common to draw a graph that links the power (unit of measurement watts) and current (unit of measurement amps) so that you have an easy-to-read tool that shows the behavior of these two correlated quantities.
Steps
Method 1 of 3: Convert Watts to Amps at a Constant Voltage
Step 1. Find the correlation chart between watts and amps
In the case of dedicated applications, such as the wiring of household electrical systems or cars, specific voltage values must be respected. Since the latter quantity in these cases always assumes a constant value, it is possible to create a table or a graph that links the values of the electrical power to those of the current. These tables are created based on the equations that link the electrical quantities involved: W, A and V. If you intend to rely on this type of instrument, you can find one directly online. Just make sure you are using the correct scheme based on the voltage applied in your case.
- For example, in Italy civil electrical systems use an alternating voltage equal to 230 V, while the electrical systems of cars use a direct voltage equal to 12 V.
- To simplify the accounts, you can use an online spreadsheet that calculates the amperes present in a circuit with these characteristics.
Step 2. Find the power value (expressed in W) you want to convert
Once you've found the correct diagram, you should scroll through its entries to find the value you need. Normally, these diagrams are made up of rows and columns. Find the column that says "Power" or "Power" or "Watt". Scroll through it to find the exact wattage relative to the electrical circuit you are currently working on.
Step 3. At this point, find the corresponding current (expressed in A)
Once you have found the watt measurement in the relative column, scroll down the row until you find the value in the "Current" or "A" column. The table you are looking at may consist of several columns, so make sure you read the value of the correct one to avoid making mistakes. Once you have located the column for electric current, carefully check the value indicated to make sure it refers to the watts you want to convert.
Method 2 of 3: Calculate Current Using Watts and Direct Voltage (DC)
Step 1. Find the circuit power value
Look for the appropriate label on the circuit you are working on. Electric power is measured in watts. This value measures the amount of energy used or created in a given period of time. For example, 1 W equals 1 Joule per second. The value of the electric power is essential to calculate the current.
Step 2. Locate the voltage
The voltage represents an electrical potential and, as for the power, it should be indicated on the label describing the circuit or device you are working on. The potential difference in an electrical circuit occurs because one side or a point of the latter is charged with electrons (due to the applied voltage) while the other is less charged. This potential difference generates a current flow from the most charged to the least charged point, in an attempt to rebalance the voltage difference. So, in order to calculate the current (or amps) flowing in the circuit, you need to know the value of the supply voltage that is applied.
Step 3. Set up the equation
For circuits powered with a direct voltage (DC) the equation to use is very simple. Electric power is equal to the product of voltage and current. Consequently, it is easy to understand that, to calculate the current, it is necessary to use the inverse formula, which involves dividing the power by the voltage.
A = W / V
Step 4. Solve the equation based on the current
Once you have the formula set up, do the math to get the amps. Divide between power and voltage to get the current. Check the units of measure to make sure you get coulombs per seconds. 1 A = 1 C / 1 s.
The coulomb (C) is the standard unit of measurement of electric charge, defined as the amount of electric charge carried in 1 second by a current flow equal to 1 ampere
Method 3 of 3: Calculate Current Using Watts and Single Phase Alternating Voltage (AC)
Step 1. Know the power factor
The power factor of an electrical circuit represents the ratio between the active power that feeds an electrical load and the apparent power that flows in the circuit. The apparent power is always greater than or equal to the active power, for this reason the power factor is always between 0 and 1. Look for this value on the diagram or on the label that characterizes the electrical circuit or the device being studied.
Step 2. Use the single-phase equation
The equation that binds voltage, current and power in a single-phase alternating voltage circuit is very similar to that used for direct current circuits. The difference lies precisely in the use of the power factor.
A = W / (FP x V) where the power factor (FP) represents a coefficient with no unit of measurement
Step 3. Solve the equation based on the current
After replacing the variables of the formula with the corresponding values of power, voltage and power factor, you can perform the calculations to obtain the current. As the resulting unit of measurement you should get C / s i.e. amperes. If not, it means you've set the equation incorrectly, so check your calculations for the error.
Calculations for circuits powered with three-phase alternating voltage involve the use of more variables than circuits powered with single-phase alternating voltage. To calculate the alternating current flowing in a circuit fed with a three-phase voltage, you will need to decide whether to use the voltage present between the neutral pole and an active conductor or between two active conductors
Advice
- Understand that you are calculating the intensity of an electric current from a power and a voltage. It is not possible to directly "convert" watts into amperes since they are two units of measurement that identify two totally different quantities.
- Help yourself by using a calculator.
