How to detect leakage of electrolytic capacitors

  1.A method for detecting leakage resistance of electrolytic capacitors using a pointer multimeter.

      First, the measurement steps.

      Dial the multimeter to the appropriate range gear, adjust zero, using the black watch pen connect the positive pole of the capacitor and the negative pole with the red watch pen, and the capacitor begins to charge, so the multimeter pointer wobbles to the right quickly. When the swing to a certain angle (charging end) will slowly back, the larger the capacity, the greater the swing angle to the right, but the watch needle cannot usually return to ∞. For electrolytic capacitors with small leakage, the leakage resistance indicated by the pointer returned to the left is usually greater than 500k Ω. If the measured resistance value is less than about 100k Ω, it indicates that the measured capacitor has leaked electricity and cannot continue to be used.

       Then exchange the watch pen, that is, the black watch pen is connected to the negative pole of the electrolytic capacitor, and the positive pole of the red watch pen connection capacitor to measure. When the watch needle is normal, the watch needle should swing to the right quickly and the swing amplitude should exceed the swing amplitude of the watch needle during the first measurement, and then return. The measured reverse leakage resistance should be greater than the forward leakage resistance.

        (1) If the watch needle does not move at the time of the above measurement or the swing amplitude of the watch needle does not exceed the second measurement, the amplitude of the wobble of the watch needle does not exceed that of the second measurement. The swing amplitude of the watch needle during the second measurement indicates that the capacitor under test has failed or the charging and discharging ability has become worse.

       (2) If the positive and reverse resistance values of electrolytic capacitance are close to 0 or ∞, it indicates that the capacitor has been broken through short circuit or open circuit failure.

       Second, the problems that must be paid attention to.

       When testing electrolytic capacitors, the following two points should be paid attention to.

       (1) Before testing the electrolytic capacitor, the two ends of the electrolytic capacitor under test should be connected briefly to remove the original stored charge.

       (2) During the test, attention should also be paid to the voltage resistance of the electrolytic capacitor, and the multimeter position used should ensure that the battery voltage does not exceed the voltage of the capacitor.

  2.The method of detecting and judging the leakage of electrolytic capacitor by using the combination of pointer multimeter and neon bubble.

     The detection circuit for judging whether the electrolytic capacitor is leakage by multimeter and neon bubble is shown in Fig. 1. The circuit can detect the leakage of electrolytic capacitor with voltage of 4-400V.

Fig. 1 Detection circuit for judging whether an electrolytic capacitor is leaking electricity by using a  multimeter and neon bubble.

      First, the principle of charging detection.

      In fig. 1, the rectifier filter circuit composed of VD1~VD4 and capacitor C converts 220 AC voltage to DC voltage (that is, the voltage at both ends of C capacitor).

      When the capacitor Cx is connected, the switch SA1 is dialed to the "1" bit, and the power supply charges the capacitor through the current limiter R and neon bubble N. Because the terminal voltage of the Cx is 0, the voltage difference between the two ends of the neon tube N is greater than the glow voltage.

      As the Cx continues to charge, the terminal voltage increases, the voltage at both ends of N decreases, and N goes out when the voltage is less than the extinguishing voltage. Because of the leakage resistance of the electrolytic capacitor itself, the voltage is discharged through the leakage resistance, and the terminal voltage of Cx decreases. The voltage difference between the two ends of       N increases, and N rekindles when the glow voltage is exceeded.

     Second, the detection method.

     Thus, it can be seen that as long as there is leakage in the capacitor to be tested, the neon bubble will flicker periodically, the higher the flicker frequency, the greater the leakage of the capacitor, on the contrary, the smAller the leakage.

     For example, if the flicker period of 10uF/250V capacitor is greater than 5 s, the leakage range can be determined to meet the requirements. At the same time, when the neon bubble goes out, reading the data on the multimeter is the pressure resistance value of Cx.

      Third, the principle of discharge detection.

When the SA1 switch is dialed to "2 bits, R3, N2 and Cx form a loop, the charged C to discharge." At this time, the discharge of C can be monitored by the lighting of neon bubble and the reading of multimeter.

When the SA1 switch is dialed to the "2" bit, the voltage difference between the N2 ends is larger than Kai Fai Voltage. With the energy consumption of R3 and N2 and the leakage of the Cx itself, the terminal voltage of the Cx decreases, and the voltage difference between the N2 ends decreases to less Kai Fai Voltage. At the same time, it can be seen that the voltage at both ends of Cx gradually decreases to 0, indicating that the discharge of Cx is over, indicating that the leakage of the capacitor is smAll. On the contrary, when the SA1 switch has just hit the "2" bit, N2 flashes a little, and the multimeter pointer quickly returns to zero, which indicates that the leakage of the electrolytic capacitor is large.

       Fourth, the problems that should be paid attention to when testing.

       (1). The leakage current should not be too large when measuring, otherwise the capacitor is easy to burst and crack. When the withstand voltage of the capacitor is low, the leakage current is about 3 mA, and when the voltage of the capacitor is high, the leakage current is about 1 mA. The size of the leakage current can be changed by adjusting the current limiter R1.

       (2). The fully charged electrolytic capacitor cannot be discharged directly by short circuit, but can be discharged with an incandescent bulb of 60 ~ 100W and 220V.

       Fifth. Leakage current and insulation resistance of various electrolytic capacitors.

       The leakage current and insulation resistance of various electrolytic capacitors are shown in Table 1. It can be used as a reference for testing.

Table 1 leakage current and insulation resistance of various electrolytic capacitors.

If you want to know more, our website has product specifications for electrolytic capacitors, you can go to ALLICDATA ELECTRONICS LIMITED to get more information