How to measure 400 microfarad capacitance with pointer multimeter
If the capacitance requirements are not very precise, it is still very convenient to measure large-capacity capacitors with a pointer multimeter.
Most of the large-capacity capacitors above several hundred microfarads are electrolytic capacitors used for filtering. This kind of capacitance generally has a relatively large error and more or less some leakage. Our requirement for this kind of capacitor is sufficient capacity and small leakage. The following is an introduction to the method and precautions for measuring capacitance with a pointer multimeter:
First, use a metal object to short-circuit the capacitor pins and discharge them. The main purpose of doing this is to eliminate danger and reduce measurement errors, because some charged capacitors are terrible when they are discharged, which will not only damage the multimeter but also may hurt people. Even if there is only a small amount of charge, which cannot be felt by the human body, it still has an impact on the measurement results.
The discharged capacitor can be measured with confidence. The second step of measurement is to choose the gear of the watch. The principle of gear selection is that the maximum range of pointer swing during measurement can be near the middle of the dial. For the capacitance of 400μF, if it is measured by MF47, it is better to choose Rx10 under normal circumstances.
When the capacitor is connected to DC, it will generate a charging current, and the larger the capacitance, the greater the current. If you use the Ω file of the pointer multimeter to measure the capacitance, it is equivalent to charging the capacitance with the battery in the meter. The larger the capacity, the greater the pointer swing.
But how much swing is 400μF? This requires finding a new capacitor with a similar capacity for comparison, for which we can choose a capacity of 470μF as a comparison standard. There may be some differences between different models of watches, but as long as the pointer can swing to the middle for comparison. According to this principle, some multimeters even mark the capacitance scale, just measure it directly.
It should also be noted that electrolytic capacitors have polarity, and the leakage current will be different when measuring reverse and positive. Connecting the negative electrode of the capacitor with a red test lead has a small leakage, and vice versa, the leakage will be larger. The closer the pointer swings back to the original position, the smaller the leakage. When simply measuring the leakage, you can also choose the Rx1K file, which can be seen in more detail. When the red test lead is connected to the negative pole, it should not be less than 1MΩ. The higher the withstand voltage, the smaller the leakage (the larger the resistance).
In addition, the capacitor must be discharged every time it is measured, otherwise the accuracy will be seriously affected.
Set the multimeter to 100Ω (resistance), short the two needles and adjust to zero. Connect the two needles to the two legs of the capacitor respectively. If the black needle is on the positive pole of the capacitor and the red needle is on the negative pole of the capacitor, this is called a forward charging measurement; otherwise, it is a reverse measurement. The swing of the hands of the forward measurement is very large, close to zero; the swing of the hands of the reverse measurement is relatively small. The method of measuring the capacitance is good or bad, no matter the forward measurement or the reverse measurement, the watch hand swings a lot and almost reaches the zero position, and then slowly swings back until it is close to infinity, indicating that the capacitance is good. If the hands of the watch directly reach the zero position without returning, it means that the capacitor has been broken down and damaged. If the watch hand hits any position in the middle and does not return, it means that the capacitor has serious leakage and cannot be used. If the hands of the watch do not move, it means that the capacitor has no capacity and cannot be used. The above is the method of measuring the quality of capacitance, and the measurement of other capacities is similar.
If the pointer needs to use a meter to measure the large capacitor, it can only simply judge whether the capacitor is short-circuited, whether the capacity is invalid, and the capacity reduction cannot be measured. Test method, adjust the meter gear to the R resistance gear 1K position, short-circuit and discharge the positive and negative electrodes of the capacitor first, connect the black pen to the capacitor negative, and the red pen to the capacitor positive, the pointer of the normal watch will turn forward and close to the short circuit, and then the pointer will indicate the resistance It will gradually become larger, and finally close to infinity, so that the capacitor is basically fine and can be used. If the test shows that the pointer resistance is very low and does not move, it means that the capacitor is short-circuited internally. If the pointer does not respond, it means that the capacitor has failed.
