How to judge whether the capacitor is good or bad?

How to judge whether the capacitor is good or bad?

How to measure the quality of small capacitor?

1. Detect small capacitors below 10PF. Because the capacity of fixed capacitors below 10PF is too small, if you use a pointer multimeter to measure, you can only qualitatively check whether there is leakage, internal short circuit or breakdown. When measuring, multimeter R can be selected × At 10K gear, connect the two pins of the capacitor with the metal measuring rods of two electric meters at will, and the resistance value should be infinite. If the measured resistance value (the indicator swings to the right) is zero, it indicates that the capacitor is damaged by leakage or internal breakdown.

2. For 0.01 μ For fixed capacitance above F, R of pointer multimeter can be used × 10K gear directly tests whether the capacitor has charging process and whether there is internal short circuit or leakage, and the capacity of the capacitor can be estimated according to the amplitude of the pointer swinging to the right.

How to detect the quality of electrolytic capacitors?

1. Since the capacity of electrolytic capacitors is much larger than that of general fixed capacitors, appropriate measuring range should be selected for different capacities during measurement. According to experience, generally, 1 ~ 47 μ Capacitance between F, R can be used × 1K block measurement, greater than 47 μ The capacitance of F can be used as R × 100 gear measurement.

2. Connect the metal measuring rod of the red meter to the negative pole and the metal measuring rod of the black meter to the positive pole. At the moment of contact, the pointer of the multimeter will deflect to the right with a large deflection (for the same electrical barrier, the larger the capacity, the larger the swing), and then gradually turn to the left until it stops at a certain position.

At this time, the resistance value is the forward leakage resistance of the electrolytic capacitor, which is slightly larger than the reverse leakage resistance. Practical experience shows that the leakage resistance of electrolytic capacitors should generally be more than hundreds of K Ω, otherwise, they will not work normally.

In the test, if there is no charging phenomenon in the forward and reverse directions, that is, the gauge needle does not move, it indicates that the capacity disappears or the internal circuit is open; If the measured resistance value is very small or zero, it indicates that the capacitor has large leakage or has been broken down and damaged, and cannot be used again.

3. For electrolytic capacitors with unclear positive and negative signs, the above method of measuring leakage resistance can be used to distinguish. That is, measure the leakage resistance at will, remember its size, and then exchange the metal measuring rod of the electricity meter to measure a resistance value. The one with the largest resistance in the two measurements is the positive connection method, that is, the metal measuring rod of the black meter is connected to the positive electrode, and the metal measuring rod of the red meter is connected to the negative electrode.

4. The capacity of the electrolytic capacitor can be estimated and measured by using the resistance block of the multimeter and the method of charging the electrolytic capacitor in the forward and reverse directions according to the amplitude of the pointer swinging to the right.

5. Measure the discharge speed of capacitance

Put a digital multimeter on both ends of the capacitor, charge it first, and then measure the speed of voltage falling in an open circuit. Because the capacitor is open circuit, the only thing that will consume power is the leakage current. If you measure the curve between voltage and time, you can deduce the leakage current. Remember to use a better digital multimeter, because the input impedance of the multimeter itself is limited, and if it is a capacitor with better quality, the leakage current is not large, Then the digital multimeter with a slightly smaller input impedance is inaccurate.

6. Attention! When measuring large capacitance, if it is necessary to measure the positive and negative back and forth, the capacitance should be short circuited and discharged to avoid damaging the meter.

According to experience, in high-frequency circuits, switching power supply circuits have many small capacitors that ordinary multimeter cannot correctly judge, and some capacitance may increase. It is strongly recommended to use a special digital capacitance meter for measurement.