How to measure a 400 microfarad capacitor with a pointer multimeter
If the capacitance requirement is not very precise, it is still 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 capacitor generally has a large error and more or less leakage. Our requirement for this kind of capacitor is sufficient capacity and small leakage will be enough. The following is a description of the method of measuring capacitance with a pointer multimeter and the precautions.
First of all, the capacitor pins should be short-circuited with metal objects to discharge them. The main purpose of doing so is to eliminate the danger of reducing the measurement error, because some of the charged capacitance in the discharge is very scary, not only will damage the multimeter may also hurt people. Even if only a small amount of charge, the human body can not feel, but still have an impact on the measurement results.
The discharged capacitor can be measured with confidence. Measurement of the first step is to choose a good meter gear. The principle of gear selection is to measure the pointer swings the largest in the center of the dial near. For 400μF capacitance such as the MF47 to measure, in general, to choose Rx10 is appropriate.
Capacitors in the moment of connecting DC power, will produce charging current, the larger the capacity of the current is greater. If the pointer multimeter Ω file to measure the capacitance, it is equivalent to using the battery inside the table to charge the capacitance. The larger the capacity, the larger the pointer swing.
But how much swing is 400μF? It is necessary to find a capacity close to the new capacitor for comparison, we can choose the capacity of 470μF as a comparative scale. Different models of the table may have some differences, but as long as the pointer can swing to the center for easy comparison can be. Based on this principle, some multimeters are even marked out the capacitance scale, direct measurement on the line.
Another point should be noted, electrolytic capacitors are polarized, reverse, positive measurement of leakage will be different. With the red pen connected to the negative side of the capacitor leakage is small, in turn, the leakage will be larger. The closer to the original position after the return of the pointer swing, the smaller the leakage. Simply measuring leakage, you can also choose Rx1K gear, you can see a little more detailed. When the red pen is connected to the negative pole should not be less than 1MΩ. the higher the withstand voltage, the smaller the leakage (the larger the resistance value).
In addition, every measurement should be discharged to the capacitor, otherwise the accuracy will be seriously affected.
Put the multimeter to 100Ω file (resistance file), the two needles shorted to zero. The two needles are connected to the capacitor legs, if the black needle on the capacitor positive, red needle on the capacitor negative, which is called positive charging measurement; otherwise, it is the reverse measurement. Positive measurement needle swing is very large, close to zero; reverse measurement needle swing is small. Measurement of capacitance good or bad method, regardless of forward measurement or reverse measurement, the needle swing is very large almost to zero position, and then slowly swing back until close to infinity, indicating that the capacitance is good. If the needle directly to zero position and not return, that the capacitor has been damaged by breakdown. If the needle hits any position in the center and does not return, it means that the capacitor can not be used because of serious leakage. If the needle does not move, the capacitor has no capacity can not be used. Above is to measure the capacitance of good and bad methods, other capacity measurement is similar.
Pointer to use the table to measure large capacitance can only be simple to determine whether the capacitor is short-circuited, whether the capacity is invalid, the capacity to reduce the measurement is not out. Test method, the table gear to R resistance gear 1K position, the capacitor positive and negative poles first short-circuit discharged under the black pen connected to the negative capacitance, the red pen connected to the positive capacitance, the normal table pointer will be close to the short circuit, and then the pointer indicates that the resistance will slowly become larger, and finally close to infinity, so that the capacitor is basically not a problem can also be used. If the test appears pointer resistance is very low immobile situation that the capacitor internal short-circuit, if the pointer does not respond that the capacitor failure.
