The Ampere is the unit of measurement of electric current, that is, of the flow of electrons in a circuit. This information can be very useful when you want to connect a tool or appliance to the power sockets in your home.
Steps
Method 1 of 3: Convert Watts to Amps
Step 1. Apply the conversion formula for direct current
You can calculate the electric current, represented by I and measured in amperes (A), by dividing the power expressed in Watts (W) by the voltage value expressed in Volts (V). This formula corresponds to the equation:
-
THE(TO) = P(W) / V(V)
Or more simply: Ampere = Watt / Volt
Step 2. Consider Power Factor (FP) for alternating current issues
This factor is a value between 0 and 1, which represents the ratio between the real power that is used to perform a job and the apparent power supplied to an alternating current circuit. Consequently, the power factor is equal to the real power P, expressed in Watts, divided by the apparent power S, measured in VoltAmpere (VA):
FP = P / S
Step 3. Calculate the apparent power to find the power factor
You can do this with the equation S = V rms x I rms
where S is the apparent power in VoltAmpere (VA), V. rms is the effective value of the voltage in Volts and I. rms is the effective value of the current; you can find the last two terms by solving the following formulas:
- V. rms = V maximum / √2 in Volts (V)
- THE rms = I maximum / √2 in Ampere (A)
Step 4. Use the power factor for single phase alternating current
The single-phase current is indicated with I and is expressed in Ampere (A). You can calculate it by dividing the real power (P) measured in Watts (W) by the power factor (FP) multiplied by the effective value (RMS) of the voltage measured in Volts (V). The equation described is represented as:
-
THE(TO) = P(W) / (FP x Vrms (V))
Or more simply: Ampere = Watt / (FP x Volt)
Method 2 of 3: Measure the Direct Current Amperage with an Ammeter
Step 1. Make sure the current is continuous
Current of this type is made up of electrons flowing in only one direction. If the circuit is powered by a battery, the current is continuous.
In many countries, including Italy, the electricity supplied by the electrical grid is in alternating current. This current can be turned into DC, but only with a transformer, rectifier and RC filter
Step 2. Determine the electrical connections
To take the measurement of the amperage of your circuit, you need to add the ammeter. Follow the two battery terminals and their connection cables to find the electrical connections.
Step 3. Test the circuit
If the circuit is open or there is a defect in the battery, the ammeter will likely fail to measure current. Turn on the circuit to check if it works normally.
Step 4. Turn off the circuit
For some simple schemes, it may be necessary to remove the battery entirely. With more powerful batteries you run the risk of electrocution, so be careful and check that the circuit is off. If in doubt, use insulated rubber gloves.
Step 5. Connect the positive terminal to the ammeter
The device has two probes: one red and one black. The red one is the positive (+) terminal of the measuring instrument, the black one the negative (-). Take the cable that starts from the positive terminal of the battery and connect it to the positive probe of the ammeter.
The ammeter does not interrupt the flow of electricity and measures the current flowing through it, displaying the value on the screen
Step 6. Complete the circuit with the negative ammeter probe
Connect the negative lead to the respective probe of the meter and complete the circuit you just cut off. Insert the wire into the destination it previously had in the circuit.
Step 7. Turn on the circuit
Often it is enough to replace the battery; the device should turn on and the ammeter should indicate current in amperes (A) or milliAmpere (mA).
Method 3 of 3: Calculate the Amperage with Ohm's Law
Step 1. Understand the concept of Ohm's law
This law relating to electricity establishes a relationship between the voltage applied to a conductor and the current flowing through it. Ohm's law is represented with the formulas V = I x R, R = V / I and I = V / R, with the terms indicating:
- V = the potential difference between two points
- R = the resistance
- I = the current flowing through the resistor
Step 2. Determine the circuit voltage
If it's powered by a 9 Volt battery, you already have an equation datum. You can find the specific voltage of the battery you are using by checking the packaging or with a quick internet search.
Almost all cylindrical batteries (from AAA up to D) provide about 1.5 Volts when they are not exhausted
Step 3. Calculate the resistance value of the circuit
Electric resistance is a physical quantity that measures the tendency of a semiconductor to resist the passage of an electric current when subjected to an electric voltage. This opposition depends on the material with which it is made, its size and its temperature. It is measured in Ohms (Ω).
- Cables where current flows also have resistance. These are usually negligible values, unless they are of poor quality, damaged or very long.
- The formula for resistance is as follows: Resistance = (resistivity x length) / area
Step 4. Apply Ohm's Law
Since the battery voltage is applied to the whole circuit, to derive the approximate value of the total current you have to divide the total potential difference for each resistive branch and then add the currents obtained. If for example we have 3 resistors in parallel, the total current will be calculated as follows:
