How to use a digital multimeter to measure the quality of capacitors and their leakage current
There are generally three types of capacitor failures: breakdown damage, large leakage current, and variable value. If you want to judge the quality of the capacitor on the machine equipment, you can use a digital multimeter to measure it. The electrician's home below introduces how to use a digital multimeter to measure the quality of the capacitor and its leakage current.
1. Judge the quality of the capacitor based on its capacitance.
Nowadays, many digital multimeters are equipped with capacitance settings, which can directly measure the capacitance. If you want to judge the quality of a capacitor, you can directly use the capacitance setting of the digital multimeter to measure its capacity to know the quality of the capacitor. When measuring, adjust the multimeter's range switch to the appropriate capacitor gear as shown in the figure above (for a multimeter that automatically changes the range, there is no need to select a gear), and use the red and black test leads to touch the two pins of the capacitor respectively (for electrolytic capacitors, There is no need to consider the pin polarity when measuring), the reading displayed by the multimeter is the capacitance. If the measured capacitance is very close to its nominal value, the capacitor is good. On the other hand, if the reading deviates greatly from the nominal value, there is something wrong with the capacitor.
If the measured capacitance is significantly less than the nominal value, it means that the capacitor is broken. Generally, if an electrolytic capacitor is left for a long time, the internal electrolyte will dry up, causing its capacity to become very small. This kind of capacitor is generally not suitable for use. If the multimeter displays a reading of "1" when actually measuring a capacitor, which means it overflows, you can use the multimeter's resistance range to measure its resistance. If the displayed resistance is very small, it means that the capacitor has broken down and been damaged. If the measured capacity of a certain capacitor is much larger than the nominal value, it means that the capacitor has a large leakage current, and generally this capacitor should not be used.
2. Measurement of capacitor leakage current
For electrolytic capacitors that have been left for a long time, the insulation performance of some will decrease, causing the leakage current to increase. If the capacity of such a capacitor with a large leakage current is measured using the capacitance scale, the displayed capacity will be larger. At this time, we can measure the capacitance. leakage current to further determine whether it is available.
When measuring leakage current, connect the measured capacitor in series to a DC ammeter (you can use the 20mA range of a digital multimeter to measure), and then connect it to a 5V DC power supply. At first, the current displayed by the ammeter is larger, and then gradually decreases until it approaches 0. Assume that after the capacitor is fully charged, the current displayed by the ammeter is not 0, indicating that the capacitor is leaking. At this time, the current displayed by the multimeter is the leakage current of the capacitor.
