How to check capacitor?

In the family of electronic components, capacitors play a pivotal role and are widely used in various types of electronic equipment, from smart phones to industrial control cabinets, none of which are missing. However, capacitors do occasionally fail. Learning how to check capacitors is like having a pair of “seeing eyes” for electronic repairs, allowing us to quickly diagnose problems and repair equipment. Today, MobikeChip will provide you with a detailed introduction to the practical methods of checking capacitors.  

The appearance of the initial examination: to capture the problem tip

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Appearance inspection of capacitors is the first step in diagnosis, which seems to be simple, but can find many potential problems. Pick up the capacitor, the first observation of its shell, the normal capacitor shell should be flat and smooth, no obvious physical damage, such as bulging, cracks, liquid leakage and other phenomena. Once found that the capacitor shell bulging, which is usually caused by excessive internal pressure, meaning that the capacitor may have been damaged, can not work properly, continue to use in this case is very likely to cause circuit failure, and even damage to other components.

Look at the pins of the capacitor, you should make sure that they are straight, not broken or bent excessively, and the connection between the pins and the casing should be firm, with no signs of looseness. If the pins are broken, the capacitor will not be able to connect to the circuit properly; while loose pins may lead to poor contact and intermittent failure of the circuit. In addition, pay attention to the logo on the surface of the capacitor, clear and complete logo to help us quickly confirm its parameters, if the logo is blurred, on the one hand, it may affect the subsequent parameters of the verification, on the other hand, also implies that the capacitor may have experienced high temperatures, humidity and other adverse environments, and the stability of its performance is in doubt. Through the appearance of the initial review, we can quickly rule out some of the problems caused by physical damage or unclear marking, to lay the foundation for in-depth inspection. 

Capacitance value measurement: accurate judgment of core performance

For electrolytic capacitors and other capacitors with polarity, when measuring, pay special attention to the polarity can not be reversed, otherwise it may damage the multimeter or capacitors. Connect the pens of the multimeter to the two pins of the capacitor and read the value shown on the display. Due to the existence of a certain degree of precision error capacitors, the actual measured value and the nominal value of a slight deviation is normal, as long as the capacitor nominal precision range, can be judged capacitance is basically normal. For example, a nominal value of 10μF, accuracy of ± 20% of the capacitor, the actual measured value between 8μF and 12μF, can be considered qualified. If the measured value deviates too much from the nominal value, even to infinity or close to zero, it indicates that the capacitor may have an open circuit, a short circuit, or a serious degradation of performance, etc., and further investigation is required.

Insulation resistance test: assessing the risk of electrical leakage

The insulation resistance of a capacitor reflects its leakage, and this indicator should not be ignored. Using an insulation resistance meter (megohmmeter) to test the insulation resistance of capacitors is a more reliable method. Connect the two output wires of the megohmmeter to the two poles of the capacitor, and according to the operating procedures of the megohmmeter, slowly crank the handle to output the rated voltage, and observe the deflection of the megohmmeter pointer.  

Under normal circumstances, the insulation resistance value of the capacitor should be very high, megohmmeter pointer should be deflected to infinity side. If the pointer deflection angle is small, the indication of the insulation resistance value is low, indicating that the capacitor has a leakage phenomenon, the leakage of serious capacitors in the circuit will consume additional power, resulting in reduced circuit efficiency, and may even lead to overheating, short-circuit and other faults. Especially in some high-voltage circuits or harsh insulation requirements of electronic equipment, such as power electronic converters, medical equipment, etc., it is critical to rigorously test the insulation resistance of capacitors to ensure the safe and stable operation of the equipment.

Voltage withstand test: Challenge the limit to ensure safety

Withstanding voltage test is the ultimate test of capacitor quality and reliability. Capacitors need to withstand a certain voltage in actual operation, if the withstand voltage is insufficient, it is very easy to break down and damage, triggering circuit failure. A professional withstand voltage tester is a necessary tool for this test.
Before the test, according to the capacitor's nominal withstand voltage value, set the output voltage of the withstand voltage tester, generally set the output voltage is slightly higher than the nominal withstand voltage value of 1.2 - 1.5 times for a certain period of time (usually 1 - 5 minutes), to observe whether the capacitor can withstand the voltage without breakdown phenomenon. 

It should be noted that the withstand voltage test is dangerous and improper operation may result in electric shock or component damage, so be sure to follow the operating procedures strictly. If the capacitor smokes, breaks down and discharges during the voltage withstand test, it means that its voltage withstand performance does not meet the requirements and cannot be used in the corresponding circuit, and it needs to be replaced with a qualified capacitor in order to ensure the safe operation of the circuit.

At MobikeChip, we not only provide high-quality capacitor products, but also dedicate ourselves to teaching you professional electronic component knowledge and inspection skills. Knowing how to check capacitors will help you in your electronic design, debugging and repairing journey. If you encounter any problems in testing, selecting or applying capacitors, please feel free to visit MobikeChip's website, and our professional team will be happy to answer your questions.   

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