Introduction to measuring the current of charging current meter with multimeter
The charger is a mobile phone charger or an electric scooter charger. However, no matter what charger it is, in order to measure the DC charging current in the circuit, it is necessary to disconnect one of the charging wires (or disconnect one of the charging wires at another location on the charging plug, and connect the red and black probes of the multimeter in series in the circuit). At this point, insert the input wire plug of the charger into a 220V power supply and observe the actual charging current between the charger and the charged load.
If it is a mobile phone charger, one charging wire needs to be discarded, and the two probes of the multimeter's DC current range need to be measured in the circuit.
Set the multimeter to the current mode and follow the principle of selecting high and then low modes, and connect it in series to the charger circuit that needs to be measured.
It should be noted that batteries generally use constant voltage charging method for fast charging. Due to the constant charging voltage, the charging current at both ends of the battery is relatively low, and the starting charging current will be large. As the voltage increases, the charging current at both ends of the battery will gradually decrease. Therefore, the charging current measured at different charging time periods is different.
There is a significant difference between lithium battery charging and battery charging. In order to protect the maximum efficiency and usage time of lithium batteries, they can generally be divided into four stages: pre charging, fast charging, make-up charging, and trickle charging. So, the charging current at any stage will also vary.
There are clamp type multimeters and ordinary multimeters. The clamp type is simple. Set the meter to the current mode, place the tested wire into the clamp ring, and read the data. Ordinary multimeters need to be connected in series to the circuit. Pay attention to the range of the meter and be careful not to burn it out. This type of meter can measure currents that are not very large and is not suitable for measuring high current circuits.
Simply connect a multimeter to the charging circuit, select DC2A for fast charging and DC500mA for slow charging. Or buy a dedicated test question for mobile phone charging, which can simultaneously detect charging voltage and battery, with dual LED display, priced at around 25 yuan, and both input and output are USI3 interfaces.
In addition, a 1 ohm resistor can be connected in series in the circuit, and the voltage across the resistor can be directly measured. The voltage value is the current value. Due to the insertion of resistors causing a decrease in overall current, the actual current may be slightly higher than the measured value. When 讠=v/R and R=1,
讠=v).
Set the multimeter to the corresponding current range. If you don't know, try to use the highest range. Generally, the highest range of a multimeter is 10A or 20A. You need to unplug the red wire and plug it into a dedicated socket. Connect one end of the charger to the battery, and connect one of the two multimeter probes to the other end of the charger and the other to the remaining end of the battery. A digital multimeter doesn't matter. If it's a pointer multimeter, you must pay attention to polarity. The red probe must be connected to the positive terminal of the charger or the negative terminal of the battery, and the black probe must be connected to the negative terminal of the charger or the positive terminal of the battery. It depends on which end you connect to.
The output current of a typical 12V charger will not exceed 8A, while a better one will have a larger output current. The multimeter probe wire is too thin and not suitable for serial detection of charger output current. It is best to use non-contact measuring instruments.
The multimeter has two current levels (mA and A). According to the instructions, insert the red and black probes into the holes, turn the multimeter to the corresponding A level, and then connect the red and black probes in series to the current circuit for measurement.
