How to test the quality of capacitors?

Update:25,Oct,2021
Summary: How to test the quality of capacitors: In the absence of special instruments, t...
How to test the quality of capacitors:
In the absence of special instruments, the quality and quality of the capacitor can be tested and judged by the resistance file of a multimeter. For a fixed capacitor with a large capacity (above 1μF), the resistance profile (R×1000) of a multimeter can be used to measure the two electrodes of the capacitor. The needle should swing in the direction of small resistance, and then slowly swing back to around ∞. Then exchange the test rod and try again. Look at the swing of the hands. The larger the swing, the greater the capacitance of the capacitor. If the test rod keeps touching the capacitor lead, the needle should be near ∞. Otherwise, it indicates that the capacitor has leakage. The smaller the resistance value, the greater the leakage and the poor quality of the capacitor; if the needle does not move at all during the measurement , Which indicates that the capacitor has failed or is open; if the needle swings but cannot return to the starting point, it indicates that the capacitor has a large leakage and its quality is not good.
For a pressure gauge with a small capacity capacitor, when measuring with a multimeter, it is often difficult to see the needle swing. At this time, you can use an external DC voltage and the DC voltage range of a multimeter to measure. The method is shown in Figure 1, that is, adjust the multimeter. To the corresponding DC voltage file, the negative (black) test rod is connected to the negative pole of the DC power supply, the positive (red) test rod is connected to one end of the capacitor under test, and the other end is connected to the positive pole of the power supply.  
When a capacitor with good performance is switched on, the needle of the multimeter should have a larger swing; the larger the capacity of the capacitor, the greater the swing of the needle. After swinging, the needle can gradually return to the zero position. If the pointer of the multimeter does not swing at the moment when the power is turned on, the capacitor is invalid or open; if the needle keeps indicating the power supply voltage without swinging, it indicates that the capacitor has been short-circuited; if the needle swings normally, it does not return to zero. , Indicating that the capacitor has leakage phenomenon, the higher the indicated voltage value, the greater the leakage capacity. It should be pointed out that the auxiliary DC voltage used to measure the capacitor with small capacity cannot exceed the withstand voltage of the capacitor under test, so as to avoid the capacitor breakdown and damage due to the measurement. To accurately measure the capacitance of a capacitor, a capacitance bridge or Q meter is required. The simple detection method mentioned above can only roughly judge the quality of the pressure gauge capacitor.  

 

 


Pointer multimeter measurement.
1. Use the resistance file of the multimeter to roughly identify the quality of capacitors above 5000PF: Use the resistance file of the multimeter to roughly identify the quality of capacitors above 5000PF (the ones below 5000PF can only judge whether the capacitor is broken). When checking, set the resistance range to the high range value, and the two test leads are in contact with the two ends of the capacitor respectively. At this time, the pointer swings quickly and then restores, and the reverse connection, the swing amplitude is greater than the first time, and then restores. Such a capacitor is good. The larger the capacity of the capacitor, the greater the movement of the meter pointer during measurement, and the longer it will take for the pointer to recover. We can compare the capacity of the two capacitors according to the magnitude of the movement of the meter pointer.
2. Use a multimeter to judge the positive and negative leads of the electrolytic capacitor: For some electrolytic capacitors with lower voltage resistance, if the positive and negative leads are not clearly marked, the leakage current can be small (large resistance value) according to the positive connection and reverse connection The characteristics of large leakage current can be judged. The specific method is: touch the two leads of the capacitor with the red and black test leads, remember the leakage current (resistance value) (the resistance value indicated when the pointer swings back and stop), and then short the positive and negative leads of the capacitor Then, swap the red and black test leads before measuring the leakage current. Judgment is based on the small leakage current indication. The lead in contact with the black test lead is the positive terminal of the electrolytic capacitor. With this method, it is more difficult to distinguish the polarity of an electrolytic capacitor with a small leakage current.     
3. Use the resistance file of a multimeter to check the quality of the electrolytic capacitor: the two leads of the electrolytic capacitor are divided into positive and negative points. When checking its quality, the resistance file of the electrolytic capacitor with lower withstand voltage (6V or l0V) It should be placed in the R×100 or R×1K gear. Connect the red test lead to the negative end of the capacitor and the black test lead to the positive end. At this time, the pointer of the multimeter will swing and then return to or near the zero position. Such an electrolytic capacitor is good. The larger the capacity of the electrolytic capacitor, the longer the charging time, and the slower the pointer swings.  
4. Check the variable capacitor with a multimeter: the variable capacitor has a set of fixed plates and a set of moving plates. Use the resistance of the multimeter to check whether there is any contact between the moving and fixed pieces. Use the red and black test pens to connect the moving piece and the fixed piece respectively. If the pointer swings, it means that there is a short circuit in the capacitor.