How to measure the current of charging current device with multimeter
When using a multimeter to measure AC or DC current, you must set the current range of the multimeter to the AC or DC range, and measure in series in the line.
For an analog multimeter, its red test lead needs to be connected to the positive output from the charger, and the black test lead needs to be connected to the electrical load being charged. If a digital multimeter is used to measure the current in the charging line, its red test leads and black test leads can still measure the value of the AC or DC current in the line even if they are connected reversely. It is just that there is a -(- negative in front of the digital multimeter display. Number).
When measuring relatively small AC or DC charging current, you can set the current range of the multimeter to the 500mA range. If you want to measure the charging current exceeding 500mA, you need to set the analog multimeter or digital multimeter to the 5A range of the analog multimeter (the MF47 multimeter usually only has a 5A DC current range except for a few models that have a 10A range), and The digital multimeter has an AC or DC current range of 10A or 20A.
Because the digital multimeter I usually use automatically changes gears, I can only use it. Other digital multimeters just need to set the gear to point to 20A. At this time, insert the red test lead into the 10th position, and the black test lead is still in the original COM jack.
I don’t know if the charger the questioner refers to is a mobile phone charger or a battery car charger. But no matter what kind of charger it is, if you want to measure the DC charging current in the line, you must cut off one of the charging wires (or cut off one of the charging wires elsewhere on the charging plug, and connect the red pen of the multimeter, The black test leads are connected in series and are in the circuit). At this time, insert the input wire plug of the charger into the 220V power supply and observe the actual charging current of the charger and the charged load.
If it is a mobile phone charger, you need to scrap a charging wire and measure the two DC current range probes of the multimeter in the line.
Set the multimeter to the current range, and select the high range first and then the low range, and connect it in series to the charger line that needs to be measured.
What should be noted here is that batteries generally use a constant voltage charging method for fast charging. Since the charging voltage remains unchanged and the points at both ends of the battery are relatively low, the charging current will be very large at the beginning. As the voltage at both ends of the battery increases, , the charging current will gradually decrease, so the charging current measured in different charging time periods is different.
There is a big difference between lithium battery charging and storage battery charging. In order to protect the maximum efficiency of lithium batteries and protect the battery life, it can generally be divided into four stages: precharging, fast charging, top-up charging, and trickle charging. Therefore, the charging current at any stage will also be different.
There are clamp multimeters and ordinary multimeters. The clamp type is simple. Adjust the meter to the current setting and put a single wire under test into the clamp ring to read the data. Ordinary multimeters need to be connected in series to the circuit. Pay attention to the range of the meter. , be careful of burning out. The current that this meter can measure will not be very large, so it is not suitable for measuring high current circuits.
Just use a multimeter to connect the charging circuit. For mobile phone charging, choose DC2A for fast charging and DC500mA for slow charging. Or buy a special test question for mobile phone charging, which can detect the charging voltage and battery at the same time. It has dual LED display, the price is about 25 yuan, and the input and output are USI3 interfaces.
In addition, you can also add a 1 ohm resistor in series to the loop, and then directly measure the voltage across the resistor. The voltage value is the current value. Since the insertion of the resistor reduces the overall current, the actual current will be slightly larger than the measured value. (蠠=v/R, when R=1,
蠠=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 the dedicated socket. With the battery connected to one end of the charger, connect one of the two test leads of the multimeter to the other end of the charger, and the other to the other end of the battery. It doesn't matter if it is a digital multimeter. If it is an analog multimeter, you must pay attention to the polarity. The red test lead must be connected to the positive pole of the charger or the negative pole of the battery, and the black test lead must be connected to the negative pole of the charger or the positive pole of the battery. It depends on which end you string in.
The output current of a general 12V charger will not exceed 8A, and the output current of a better one will be very large. The multimeter lead wire is too thin and is not suitable for series detection of the charger output current. It is best to use non-contact measuring instruments.
There are current levels on the multimeter (two levels, mA and A). According to the instructions, insert the red test lead and black test lead into the hole, set the multimeter to the corresponding A range, and then connect the red and black test leads in series to the current loop to measure.
