How to Measure Output Current of Power Supply

Have you ever wondered how to measure the output current of power supply? Let's walk you through the various power supply measurement methods.

Current is one of the essential electrical parameters and is often measured to check how well a power supply is functioning. Typically, a current measurement will be made using a multimeter, a relatively simple process. Despite this, there are several methods of measuring current and two separate models of multimeter. So, what is the process of measuring output current?

Basic Current Measurement

The current is simply made up of a flow of electrons around a circuit. In a basic circuit, the current level can be determined by the brightness of the bulb, and this level can be adjusted by using resistors. However, a multimeter is often incorporated into the circuit for a more accurate current reading. The current must flow through the multimeter to attain a reading, so it must be placed within the circuit.

For a multimeter to function at its full effect, the resistance within the existing circuit will need to be as low as possible. This will ensure that the multimeter is not affecting the operation of the circuit. As a rule of thumb, the resistance of a meter should be significantly lower than an ohm. Otherwise, the voltage will be greatly altered.

Analogue Multimeters

One model of the multimeter is an analogue multimeter. To use one of these, you should place the probes into the right connections; it’s important to get this right as there could be separate connections that aren’t suitable. Once you have accurately connected the probes, you can set the switch to the right measurement mode and select a measurement range. You should set the switch to measure current and set the range above the anticipated maximum. If necessary, you can reduce this later, but you should always initially set it higher to prevent the meter from being overloaded.

To reach the most accurate reading, you should tweak it to gain the maximum deflection. After the reading, you should connect the probes to the voltage measurement sockets and put the range in the maximum voltage position. This minimises the risk of the meter obtaining damage. However, this may be a problem if it’s left ready for current reading and the meter is linked across a high voltage point.

Digital Multimeters

The second model of the multimeter is a digital multimeter. To use this model, you should turn the meter on and place the probes into the right connections. Typically, there will be several connections for the probes, including one labelled as common in which the black probe should be inserted. The other probe should be placed into the specific current measurement socket.

After this, you should set the main selector switch to the suitable measurement type and set the range. Once again, you should always set this above what is expected of the current. As you measure the current, you should aim not to have the leading digits as zero. Finally, you should execute the previously mentioned process of connecting the voltage measurement sockets upon completing the reading.

Series Resistors

When it’s foreseen that a current may need to be measured regularly, a series resistor may offer advantages for measuring current. This technique consists of a resistor of relevant value being placed within a circuit to measure the voltage to calculate the circuit. Despite this, the resistor’s value must be accurate to make proper measurements.

Current Sensors/Coils

Since each of the aforementioned methods require the circuit to be broken, they can’t be used for power supplies wherein the circuit can be broken. Instead, you should use current sensors or coils as the circuit doesn’t need to break for these to come into effect. Normally, current sensors are placed around the current-carrying conductor and detect the current flowing through the conductor.

For this method of measuring current, you can use a current transformer or a hall effect sensor. The current transformer is among the most common current sensors and comprises a soft iron ring or split ferrite with a coil wound around it. The core is passed over the conductor so the current can be measured. On the other hand, a hall effect sensor uses a different technology. Usually, it’s used alongside high-end digital multimeters and oscilloscopes.

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