How to measure a 400 microfarad capacitor with an analog multimeter
Most high-capacity capacitors with a capacitance of several hundred microfarads or more are 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 are the methods and precautions for measuring capacitance with a pointer multimeter
Firstly, a metal object should be used to short-circuit the capacitor pins and discharge them. The main purpose of doing this is to eliminate danger and reduce measurement errors, as some charged capacitors can be very dangerous when discharged, 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 first step in measuring is to select the gear of the watch. The principle of gear selection is that the maximum amplitude of pointer swing during measurement can be near the middle of the dial. For measuring a capacitance of 400 μ F using MF47, it is generally advisable to choose Rx10.
At the moment when a capacitor is connected to direct current, it will generate a charging current, and the larger the capacitance, the greater the current. If the Ω range of a pointer 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 swing amplitude of the pointer.
But what exactly is the swing of 400 μ F? We need to find a new capacitor with a similar capacity for comparison, and we can choose a capacitor with a capacity of 470 μ F as the comparison scale. Different models of watches may have some differences, but as long as the pointer can swing to the middle for comparison, it's enough. According to this principle, some multimeters even indicate the capacitance scale and can be directly measured.
Another thing to note is that electrolytic capacitors have polarity, and the leakage current measured in reverse and forward directions will be different. Using a red probe to connect the negative terminal of a capacitor will result in less leakage, while conversely, the leakage will be greater. The closer the pointer swings back to its original position, the smaller the leakage. When simply measuring leakage, the Rx1K range can also be selected for a more detailed view. When the red probe is connected to the negative terminal, it should not be less than 1M Ω. The higher the withstand voltage, the smaller the leakage (the larger the resistance).
