Causes of damage to electrolytic capacitors and measurement methods of leakage resistance

Electrolytic capacitors are used in large amounts in electrical equipment and have a high failure rate. Electrolytic capacitor damage has the following manifestations: one is the complete loss of capacity or the capacity becomes smaller; the second is slight or severe leakage; the third is the loss of capacity or the capacity becomes smaller and there is leakage.

"Electrolytic capacitor" refers to a capacitor formed by anodic oxidation on the surface of metals such as aluminum, tantalum, niobium, and titanium to form a thin layer of oxide as the dielectric and the electrolyte as the cathode.

Leakage resistance measurement method of electrolytic capacitor and detailed explanation of the process and matters needing attention.

Leakage current is one of the three main performance indicators of electrolytic capacitors (capacitance, loss tangent and leakage current). Excessive leakage current will directly affect the filtering and DC blocking effects of the capacitor in the circuit. In the long-time timing circuit of the capacitor, this index has a greater impact on the timing of the circuit. Therefore, it is necessary to test this important index before making a circuit with higher requirements.

Find the damaged electrolytic capacitor method:

(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 on the surface of the capacitor. This type of capacitor can no longer be used; some capacitors will bulge after damage, and this type of capacitor cannot continue. use;

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

(3) There is electrolyte inside the electrolytic capacitor. Long-time baking will cause the electrolyte to dry out and reduce the capacitance. Therefore, it is important to check the capacitors near the heat sink and high-power components. The closer they are, the damage may be possible. The greater the sex.

Find the damaged electrolytic capacitor method

Usually, electrolytic capacitors are damaged due to the following reasons:

, the rectifier tube is damaged

When a rectifier tube in the rectifier bridge is broken down, the rectified voltage will have an AC component, a reverse voltage will appear on the filter capacitor, and the filter capacitor will be damaged.

, uneven voltage distribution

When one of the voltage-balancing resistors is damaged, the voltage distribution on the two sets of capacitors connected in series with each other becomes unbalanced, and the capacitor with a higher voltage is easily damaged.

, the capacitor leakage current is too large

When the electrolytic capacitor is connected to the circuit, there is leakage current. Under normal circumstances, the leakage current is very small. However, if the capacitor is aging, or due to the poor quality of the capacitor itself, the leakage current will increase, and the electrolytic capacitor will be damaged due to severe heating.

Leakage resistance measurement method of electrolytic capacitor:

When using a multimeter to detect the leakage current of an electrolytic capacitor, connect the red test lead of the multimeter to the negative electrode of the electrolytic capacitor and the black test lead to the positive electrode. The larger the amplitude), then gradually turn to the left until it stops at a certain position. The resistance value at this time is the forward leakage resistance of the electrolytic capacitor. The larger the value, the smaller the leakage current and the better the capacitor performance.

Then, swap the red and black test leads for testing. The pointer of the multimeter will repeat the above-mentioned swing, but the measured resistance is the reverse leakage resistance of the electrolytic capacitor, which is slightly smaller than the forward leakage resistance, that is, the reverse leakage current is greater than the forward leakage current.

Practical experience shows that the leakage resistance of electrolytic capacitors should generally be more than several hundred kiloohms, otherwise it will not work normally. In the detection, if there is no charging phenomenon in the forward and reverse directions, that is, the pointer does not move, it means that the capacity of the capacitor has disappeared or the internal circuit is open; if the resistance value is very small or zero, it means that the capacitor is leaking or has been broken down and cannot be used. .

When testing, pay attention to selecting the appropriate range. Generally, the capacitance of 1~47uF can be blocked by Rx1kΩ, and the capacitor larger than 47uF can be blocked by Rx 100Ω. When the withstand voltage value of the capacitor is greater than the internal battery voltage value of the universal clothing, according to the characteristics of small leakage current when the electrolytic capacitor is charged in the forward direction and large leakage current in the reverse charging, the Rx10kΩ block can be used to reverse charge the electrolytic capacitor and observe Whether the watch hand stays is stable (that is, whether the reverse leakage current is constant), the quality of the capacitor is judged from this, and the accuracy is high.