Measuring method of leakage resistance of electrolytic capacitor

The electrolytic capacitor refers to a capacitor formed by anodic oxidation of a surface of a metal such as aluminum, ruthenium, iridium or titanium to form a thin layer of oxide as a dielectric and an electrolyte as a cathode. This paper mainly introduces the measurement method and process details of the leakage resistance of electrolytic capacitors and the matters needing attention.

The use of electrolytic capacitors:

1. DC blocking: The role is to prevent DC from passing and let the AC pass.

2. Bypass (decoupling): Provides a low impedance path for certain parallel components in an AC circuit.

3. Coupling: as a connection between two circuits, allowing AC signals to pass through and be transmitted to the next stage of the circuit

4. Filtering: This is very important for DIY, the capacitance on the graphics card is basically this effect.

5. Temperature compensation: compensates for the influence of other components on the temperature, and compensates to improve the stability of the circuit.

6. Timing: The capacitor is used in conjunction with a resistor to determine the time constant of the circuit, with a time constant t = RC.

7. Tuning: System tuning of frequency-dependent circuits such as cell phones, radios, and televisions.

8. Rectification: Turns the semi-closed conductor switching element on or off at a predetermined time.

9. Energy storage: Stores electrical energy for release when necessary. For example, camera flash, heating equipment, etc.

The working voltage of the electrolytic capacitor is 4V, 6.3V, 10V, 16V, 25V, 35V, 50V, 63V, 80V, 100V, 160V, 200V, 300V, 400V, 450V, 500V, and the operating temperature is -55°~+155°C ( 4~500V), characterized by large capacity, large volume and polarity, generally used for filtering and rectification in DC circuits. The most commonly used electrolytic capacitors are aluminum electrolytic capacitors and tantalum electrolytic capacitors.

Find ways to find damaged electrolytic capacitors:

(1) Look: Some capacitors will leak when they are damaged. There will be a layer of oil on the surface of the circuit board under the capacitor or even the surface of the capacitor. This capacitor can never be used again. Some capacitors will bulge after being damaged. continue to use;

(2) Touch: Some electrolytic capacitors with serious leakage will heat up after starting up, and even hot when touched with fingers, this capacitor must be replaced;

(3) There is electrolyte inside the electrolytic capacitor. If it is baked for a long time, the electrolyte will dry out, resulting in a decrease in capacitance. Therefore, it is necessary to check the capacitance near the heat sink and high-power components. The closer to it, the possibility of damage. The greater the sex.

Measuring method of leakage resistance of electrolytic capacitor:

1. Select the appropriate range of the multimeter, connect the red test lead to the negative pole of the electrolytic capacitor, and connect the black test lead to the positive pole of the electrolytic capacitor. At this time, the hand is swung in the direction of R, and after swinging to a certain amplitude, it is reversed to the poor. The direction swings until a certain position stops. At this time, the resistance value indicated by the pointer is the positive leakage resistance of the electrolytic capacitor. The larger the positive leakage resistance, the better the performance of the capacitor and the smaller the leakage current. The red and black test leads of the multimeter are reversed (the red pen is connected to the positive pole and the black test lead is connected to the negative pole), and then the measurement is performed. At this time, the resistance value indicated by the pointer is the reverse leakage resistance of the capacitor, and the value should be smaller than the forward leakage resistance. . If the measured values of the two leakage resistors are small (several hundred kiloohms or less), the performance of the electrolytic capacitor is poor and cannot be used.

Because the capacity of electrolytic capacitors is much larger than that of general fixed capacitors, the appropriate range should be selected for different capacities when measuring. According to experience, in general, the capacitance between 1 ~ 47μF can be measured by R × 1k block, and the capacitance larger than 47μF can be measured by R × 100 block.

For an electrolytic capacitor in which the positive and negative signs are unknown, the above method for measuring the leakage resistance can be used for discrimination. That is, first measure the leakage resistance arbitrarily, remember its size, and then exchange the test leads to measure a resistance value. The one with a large resistance value in the two measurements is the forward connection method, that is, the black meter is connected to the positive pole, and the red meter is connected to the negative pole.

2. Discrimination of positive and negative electrodes of electrolytic capacitors The method for judging positive and negative electrodes of electrolytic capacitors is mainly based on the method of measuring leakage resistance according to the above. Use the ohmic block of the multimeter to select the appropriate range according to the capacity of the electrolytic capacitor, measure the leakage resistance of the two pins of the capacitor with two meter pens, and record the magnitude of the resistance, then adjust the leakage resistance of the two test leads. The value is compared with the leakage resistance value measured twice, and the leakage resistance value is small once, and the black test pen is in contact with the negative electrode of the electrolytic capacitor.

Pay attention to the following three points when testing capacitors with a multimeter:

1） Regardless of the measurement of the leakage resistance of the capacitor, or the measurement of the short circuit and the open circuit, it is necessary to pay attention to the fact that the hand cannot touch the two leads at the same time.

2）Because the capacitor must be charged and discharged during the measurement process, after the first measurement, it must be discharged first (short the two leads of the capacitor with a multimeter) before the second measurement can be performed.

3） When detecting the capacitors in the circuit, it is necessary to find out whether other components of the circuit affect the measurement results. In general, the road measurement should be avoided.