How to measure capacitor quality using a digital multimeter
Adjust the range switch of the digital multimeter to the appropriate range of the capacitor, and then insert the red and black probes of the multimeter into the Cx and COM sockets of the multimeter (for the convenience of taking photos, a test wire with a crocodile clip is used instead of the probe). Then, the red and black probes are respectively connected to the two pins of the capacitor (if measuring electrolytic capacitors, polarity can be omitted). If the value displayed on the multimeter is close to the nominal value of the capacitor (usually with an error of 5% to 10% allowed), it indicates that the capacitor is good.
For a capacitor that has been damaged by breakdown, the resistance between its two pins is very small. At this time, when measuring with a multimeter in capacitance mode, the instrument will display "1", indicating overflow. Therefore, when measuring the capacitor, if the range switch position of the multimeter is not set incorrectly, but the instrument displays "1", it is likely that the capacitor has been damaged by breakdown or has too much leakage (at this time, the resistance value of the multimeter can be measured in resistance mode to confirm whether it is damaged).
For electrolytic capacitors that have been placed for a long time, some of the electrolytes inside the capacitors will gradually dry up, making their capacity very small. Therefore, when measuring electrolytic capacitors, if the displayed capacity is significantly lower than its nominal value, the capacitor is generally not suitable for use. The above figure shows a 100 μ F electrolytic capacitor that has been stored for several years, with a measured capacity of only 54.08 μ F.
To distinguish between good and bad capacitors, a multimeter can be used, which provides three methods for reference. Before measuring, the capacitor needs to be discharged, which will not be repeated in the following text.
1. Direct measurement
If the measured capacitance is smaller than the maximum range of the multimeter, it can be directly measured using the multimeter. If the capacitance is normal, the corresponding capacitance size will be displayed on the multimeter screen. The measured capacitance size can be compared with the labeled capacitance size. If these two are equal or close, it can be determined that the capacitance is good.
2. Diode gear measurement
If you want to distinguish that the capacitance size has exceeded the range of the multimeter, you need to use the diode range of the multimeter. Similarly, connect the probe to both ends of the capacitor. If you see that the number is increasing on the dial, and the larger the capacitance, the more obvious this phenomenon, then it can be concluded that the measured capacitance is also good.
3. Resistance measurement
This method is similar to the second method, which can be used when the capacitance exceeds the range of the multimeter. First, turn the pointer to the resistance range, and then connect the pointer to both ends of the capacitor. If you can see the number increasing continuously on the dial of the multimeter, and the larger the capacitor, the slower the increase, then you can judge that the capacitor is good. If the number 1 is always displayed on the dial, then the capacitor is broken.
