Detection method of electrolytic capacitor
1. Detection when the circuit is disconnected
When testing electrolytic capacitors, you first need to use the R×1K scale of the multimeter. Before testing, the two pins of the capacitor should be brought into contact to discharge the remaining charge in the capacitor. When connecting the test lead of the multimeter, if the meter needle deflects to the right and then slowly rotates and finally stops, then the resistance value displayed at the stop position is the leakage resistance of the capacitor. Ideally, this resistance should be as large as possible, close to infinity. If the leakage resistance is low, such as only a few tens of kiloohms, it indicates that the capacitor has a serious leakage problem. The greater the needle swings to the right and the degree to which it can swing back, usually indicates a larger capacitance.
2. Direct detection on the circuit
This detection method is mainly used to determine whether the capacitor has an open circuit or has broken down. Use the R×1 scale of the multimeter to measure. After disconnecting the power supply, first discharge the remaining charge in the capacitor. If the needle does not deflect to the right when measuring, it may indicate an internal open circuit in the capacitor. If the resistance value displayed after the meter needle deflects to the right is very small (close to a short circuit), it indicates that the capacitor has serious leakage or breakdown. If the needle deflects to the right without swinging back, but the resistance is not very small, it is likely that the capacitor is open circuit, and it should be further separated from the circuit for detection.
3. Detection when the circuit is powered on
If you suspect that the capacitor has breakdown failure only when it is powered on, you can use the DC voltage range of a multimeter to measure the voltage across the capacitor after power is on. If the voltage is very low or 0V, this indicates that the capacitor has broken down.
For situations where the positive and negative polarities of the electrolytic capacitor are unclear, the positive and negative poles should be determined first. The method is to exchange the test pens of the multimeter and conduct two measurements. The one with the larger leakage (lower resistance value) shall prevail. At this time, one end of the black test pen is the negative pole and the other end is the positive pole.
Selection Guide for Electrolytic Capacitors
1. Try to choose the same electrolytic capacitor as the original model.
2. Generally, the capacitance deviation of electrolytic capacitors is large, but this usually does not have a serious impact on the normal operation of the circuit. Therefore, you can choose a capacitor with a slightly larger or smaller capacitance for replacement. However, in key circuits such as frequency division circuits, S correction circuits, oscillation loops and delay loops, the capacitance should be consistent with the calculation requirements as much as possible. In some filter networks, the capacitance of the capacitor also needs to be very accurate, and the error should be less than ±0.3% to 0.5%.
3. The withstand voltage requirements must be met, and the selected withstand voltage value should be equal to or greater than the original value.
4. For non-polar electrolytic capacitors, they should generally be replaced with non-polar electrolytic capacitors. If you really can't find a suitable one, you can use two polarized capacitors with twice the original capacity to replace them in series. The method of reverse series connection is to connect the same polarity ends of two polarized electrolytic capacitors together.
5. When selecting electrolytic capacitors, it is best to use high-temperature resistant electrolytic capacitors. High temperature resistant capacitors can guarantee about 2000 hours of normal working time at the maximum operating temperature of 105°C. When using an 80°C capacitor in a 50°C environment, its lifespan can reach about 22,000 hours, and when using a high-temperature-resistant electrolytic capacitor, its lifespan can reach about 90,000 hours.