How to measure a 400 microf capacitor using a pointer multimeter
If the requirements for capacitance are not very precise, it is still very convenient to measure large capacity capacitors with a pointer multimeter.
Large capacity capacitors with a capacity of several hundred microfarads or more are mostly electrolytic capacitors used for filtering. This type of capacitor generally has a relatively large error and may have some leakage to some extent. Our requirements for this type of capacitor are sufficient capacity and low leakage. Below is an introduction to the method and precautions for measuring capacitance with a pointer type multimeter:
Firstly, short-circuit the capacitor pins with a metal object and perform discharge treatment on them. The main purpose of doing so is to eliminate hazards and reduce measurement errors, as some charged capacitors can be very scary during discharge, not only damaging the multimeter but also potentially injuring people. Even if there is only a small amount of charge that the human body cannot feel, it still has an impact on the measurement results.
The discharged capacitor can be measured with confidence. The next step in measurement is to select the gear of the meter. The principle of gear selection is that the maximum amplitude of the pointer swing during measurement can be near the middle of the dial. For 400 μ If the capacitance of F is measured using MF47, it is generally advisable to choose Rx10.
When a capacitor is connected to direct current, it will generate charging current, and the larger the capacitance, the greater the current. If the Ω range of a pointer type multimeter is used to measure capacitance, it is equivalent to charging the capacitor with the battery inside the meter. The larger the capacity, the greater the oscillation amplitude of the pointer.
But exactly how much swing is 400 μ What about F? We need to find a new capacitor with a similar capacity for comparison, and we can choose a capacity of 470 for this μ F serves as a comparative scale. Different models of watches may have some differences, but as long as the pointer can swing to the middle for comparison, it is sufficient. According to this principle, some multimeters even have capacitance scales marked and can be measured directly.
Another point to note is that electrolytic capacitors have polarity, and the leakage measured in reverse and forward directions will be different. Connecting the red probe to the negative electrode of the capacitor will result in a smaller leakage, while the reverse will result in a larger leakage. The closer the pointer swings back to the original position, the smaller the leakage. When simply measuring leakage, Rx1K mode can also be selected for a more detailed view. The red probe should not be less than 1M Ω when connected to the negative pole. The higher the voltage resistance, the smaller the leakage (the greater the resistance).
In addition, discharge the capacitor every time the measurement is made, otherwise it will seriously affect accuracy.
Express the multimeter to the 100 Ω range (resistance range) and short circuit the two gauge pins to zero. Lap the two pins of the capacitor separately. If the black pin is placed on the positive pole of the capacitor and the red pin is placed on the negative pole of the capacitor, this is called forward charging measurement; On the contrary, it is a reverse measurement. The swing amplitude of the forward measuring needle is very large, close to zero; The swing of the reverse measuring needle is too small. The method for measuring the quality of capacitance, whether measured in the forward or reverse direction, involves a large swing of the meter needle to almost zero position, and then slowly swinging back until it approaches infinity, indicating that the capacitance is good. If the watch needle directly reaches the zero position without returning, it indicates that the capacitor has been broken down and damaged. If the watch needle reaches any position in the middle but does not retract, it indicates that the capacitor has severe leakage and cannot be used. If the watch needle does not move, it indicates that the capacitor has run out of capacity and cannot be used. The above is the method for measuring the quality of capacitance, and the measurement of other capacities is also similar.
The pointer can only be used to measure large capacitance with a meter to simply determine whether the capacitor is short circuited, whether the capacity is ineffective, and if the capacity is reduced, it cannot be measured. Test method: Set the meter to the R resistance gear 1K position, short-circuit and discharge the positive and negative terminals of the capacitor first, connect the black pen to the negative terminal of the capacitor, and connect the red pen to the positive terminal of the capacitor. The normal meter pointer will turn forward and approach the short circuit, then the pointer will indicate that the resistance will gradually increase, and finally approach infinity. This way, the capacitor can still be used without any problems. If the pointer resistance is very low and does not move during the test, it indicates an internal short circuit in the capacitor. If the pointer does not respond, it indicates that the capacitor has failed.
