How to measure the quality of capacitor and its leakage current with a digital multimeter
There are generally three types of capacitor faults: breakdown damage, high leakage current, and variable value. To determine the quality of capacitors on machine equipment, use a digital multimeter to measure them. Below, Electrician's Home will introduce the method of measuring the quality and leakage current of capacitors using a digital multimeter.
1. Judging the quality of a capacitor based on its capacitance
Measure the capacitance with a digital multimeter.
Nowadays, many digital multimeters come with a capacitance range, which allows for direct measurement of capacitance. To determine the quality of a capacitor, simply use the capacitance range of the digital multimeter to measure its capacity and determine its condition. When measuring, adjust the range switch of the multimeter to the appropriate capacitor position as shown in the above figure (for multimeters with automatic range changing, the gear does not need to be selected), and use red and black probes to touch the two pins of the capacitor (for electrolytic capacitors, pin polarity does not need to be considered during measurement). The reading displayed on the multimeter is the capacitance. If the measured capacitance is very close to its nominal value, it indicates that the capacitance is good. On the contrary, if the reading deviates significantly from the nominal value, it indicates that there is a problem with the capacitor.
If the measured capacitance is significantly lower than the nominal value, it indicates that the capacitor is damaged. Generally, if electrolytic capacitors are left for a long time and the internal electrolyte dries up, their capacity will become very small, and these capacitors are generally not suitable for use. If a multimeter shows a reading of "1" when measuring a certain capacitor, indicating overflow, the resistance value can be measured using the multimeter's resistance range. If the displayed resistance value is very small, it indicates that the capacitor has been broken down and damaged. If the measured capacity of a capacitor is much larger than the nominal value, it indicates that the capacitor has a large leakage current, and generally this type of capacitor is not suitable for use.
2. Measurement of capacitor leakage current
Measurement method for capacitor leakage current.
For electrolytic capacitors that have been stored for a long time, their insulation performance may decrease, leading to an increase in leakage current. If the capacitance of these capacitors with high leakage current is measured in the capacitance range, the displayed capacity will be slightly larger. At this time, we can measure the leakage current of the capacitor to further determine whether it is usable.
When measuring leakage current, connect the measured capacitor in series to a DC ammeter (which can be measured using the 20mA range of a digital multimeter), and then connect it to a 5V DC power supply. At the beginning, the ammeter displays a large current, which gradually decreases until it approaches 0. Assuming that after the capacitor is fully charged, the current displayed on the ammeter is not zero, it indicates that the capacitor is leaking. At this time, the current displayed on the multimeter is the leakage current of the capacitor.
