Detection and selection of electrolytic capacitors

First, the detection of electrolytic capacitors

1. Detection when disconnecting from the line

Use a multimeter R × 1K file. Before testing, touch the two pins of the electrolytic capacitor to release the remaining charge in the capacitor. When the pen is just turned on, the hand is deflected to the right by an angle, and then the hand slowly turns to the left, and finally the hand stops. The resistance indicated by the hand stopping is the leakage resistance of the capacitor. The larger the resistance, the better, preferably close to infinity. If the leakage resistance is only a few tens of kiloohms, it means that the electrolytic capacitor has serious leakage. The greater the angle of the hand swinging to the right (the hand should also swing back to the left), the greater the capacitance of the electrolytic capacitor, and vice versa, the smaller the capacity.

2. Direct detection on the line

The main purpose is to detect whether it has been opened or broken down. These two obvious faults, and the leakage fault is generally uncertain due to the influence of the external circuit. Use the multimeter R × 1 gear. After the circuit disconnects the power supply, first discharge the residual charge in the capacitor. If the dial does not deflect to the right during measurement, it means that the electrolytic capacitor is internally disconnected. If the resistance indicated by the dial after deflecting to the right is very small (close to short circuit), it means that the capacitor is seriously leaking or has been broken down. If the dial does not rotate after deflecting to the right, but the indicated resistance value is not very small, it means that the capacitor may be very open and should be disconnected from the circuit for further detection.

3. Detection of power-on status on the line

If it is suspected that the electrolytic capacitor has a breakdown fault only when it is powered on, the circuit can be energized, and then the DC voltage across the capacitor can be measured with a multimeter. If the voltage is very low or 0 volts, the capacitor has broken down.

If the positive and negative polarity of the electrolytic capacitor is unclear, its positive and negative electrodes must be identified first. Measure the multimeter pen twice, subject to the one with large leakage (small resistance value). One foot of the black watch pen is the negative electrode, and the other foot is the positive electrode.

Second, the selection of electrolytic capacitors

1. Use the prototype electrolytic capacitor as much as possible.

2. Generally, the capacitance deviation of electrolytic capacitors is larger, which will not seriously affect the normal operation of the circuit, so capacitors with slightly larger or smaller capacitance can be replaced. However, it does not work in frequency division circuits, S correction circuits, oscillation circuits and delay circuits. The capacitance should be as consistent as possible with the calculation requirements. In some filtering networks, the capacitance of electrolytic capacitors is also required to be very accurate, and the error should be less than ± 0.3-0.5.

3. The pressure resistance requirements must be met, and the selected pressure resistance value should be equal to or greater than the original value.

4. Non-polar electrolytic capacitors are generally replaced by non-polar electrolytic capacitors. When there is no way, they can be replaced by two polar capacitors with twice the capacity in reverse series. The method is to connect the positive electrodes of two polar electrolytic capacitors (or connect their two negative electrodes).

5, in the selection of electrolytic capacitors, it is best to use high temperature electrolytic capacitors, high temperature capacitors maximum operating temperature of 105 ℃, when it works at the highest operating temperature conditions, can ensure about 2000 hours of normal working time. When using 80 ℃ capacitor at 50 ℃, its life can reach 22,000 hours, if the use of high temperature electrolytic capacitors at this time, its life can reach 90,000 hours.