# How to judge whether the capacitor is good or bad?

How to measure the quality of small capacitance?
1. Detect the small capacitor below 10pF. Because the capacity of the fixed capacitor below 10pF is too small, if the pointer type is measured with a multimeter, it can only be qualitatively checked whether there is leakage, internal short circuit or breakdown phenomenon.
When measuring, the multimeter R× 10K block can be selected, and the two metal measuring rods of the meter can be arbitrarily connected to the two pins of the capacitor, and the resistance value should be infinite. If the resistance value (indicator swing to the right) is zero, it indicates that the capacitor is damaged by leakage or internal breakdown.
2, for more than 0.01μF fixed capacitance, available pointer type multimeter R× 10K block direct test capacitor charging process and whether there is an internal short circuit or leakage, and can be estimated according to the amplitude of the pointer to the right capacitor capacity.
How to detect the quality of electrolytic capacitor?
1, because the capacity of the electrolytic capacitor is much larger than the general fixed capacitance, so, when measuring, should choose the appropriate range for different capacity. According to experience, in general, the capacitance between 1 and 47μF can be measured by R× 1K block, and the capacitance greater than 47μF can be measured by R×100 block.
2, the multimeter red meter metal measuring rod is connected to the negative pole, the black meter metal measuring rod is connected to the positive pole, at the moment of just contact, the multimeter pointer is to the right deflection larger skewness (for the same electrical block, the larger the capacity, the larger the swing), and then gradually turn to the left, until it stops in a certain position.
The resistance value is the forward leakage resistance of the electrolytic capacitor, which is slightly greater than the reverse leakage resistance. Practical experience shows that the leakage resistance of electrolytic capacitor should be more than a few hundred kω, otherwise, it will not work normally.
In the test, if the forward and reverse are no charging phenomenon, that is, the needle does not move, it indicates that the capacity disappears or internal circuit; If the measured resistance value is small or zero, it indicates that the capacitor leakage is large or has been broken down and can not be used again.
3. For electrolytic capacitors with unknown signs of positive and negative poles, the above method of measuring leakage resistance can be used to discriminate. That is, any leakage resistance is measured first, remember its size, and then exchange the meter metal rod to measure a resistance value. The resistance of the two measurements is the first time is the positive connection method, that is, the black meter metal measuring rod is connected to the positive electrode, the red meter metal measuring rod is connected to the negative electrode.
4, the use of a multimeter block, using the electrolytic capacitor for positive and reverse charging method, according to the pointer to the right swing amplitude, the capacity of the electrolytic capacitor can be estimated.
5. Measure the speed of capacitor discharge
Using a digital multimeter on both ends of a capacitor charging first then open circuit measurement voltage drop down because the speed of the capacitance is open only consumes power is the leakage current amount if you measure voltage with time curve can be deduced the leakage current remember with better digital multimeter, because the input impedance of the multimeter itself again big is limited, If the quality of the capacitor leakage current is not large, then the input impedance of a slightly smaller digital multimeter is not allowed.
6. Pay attention! If you need to measure the positive and negative back and forth when measuring a large-capacity capacitor, discharge the capacitor in short circuit to avoid damaging the meter head.
According to experience, in the high-frequency circuit, the switching power supply circuit has a lot of small capacitance is ordinary multimeter can not correctly judge the good or bad, some capacitance may also increase the possibility. It is strongly recommended to use a dedicated digital capacitance meter.