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How to judge the positive and negative of the capacitor? What caused the explosion of the capacitor?

163.com | 24/05/2021

If a capacitor explodes, its power cannot be underestimated. For a capacitor with polarity, the positive and negative poles are connected reversely, such as a tantalum capacitor. If the positive and negative poles are connected reversely, the capacitor will be burnt at the slightest, and the capacitor will explode. So what are the reasons that caused the capacitor to explode?

Judging the positive and negative poles of a capacitor can be done from many aspects. First, it is identified by appearance. The positive and negative poles are generally electrolytic capacitors. The simple and intuitive way for the new capacitor is to look at the length of the pin, which is positive and short is negative. As an electrolytic capacitor, an obvious monochrome mark is usually printed to mark the polarity. For tantalum electrolytic capacitors, the marked end is the positive electrode, while the aluminum electrolytic capacitor is the negative electrode.

In addition, the ohm file of the multimeter can also be used to distinguish the positive and negative electrodes of the electrolytic capacitor. The reason why electrolytic capacitors need to be divided into positive and negative poles is because the leakage is relatively large when they are reversely connected. We can use this feature to easily distinguish the polarity of the capacitor with an ohmmeter. For example, we use analog multimeter Rⅹ1K file to measure. When the pointer swings once, it returns slowly, and if it does not return to its original position, it is a leakage. Anyway, each test is done once, and the red test lead contact terminal is the positive electrode when the leakage is large. If the polarity of the digital meter is opposite.

The damaged capacitor on the circuit board can be replaced according to the positive and negative poles marked on the circuit board. You can also refer to the connection of other capacitors on the board. This is actually very simple. SMD capacitors basically have no positive and negative poles. Generally cylindrical electrolytic capacitors, solid capacitors have positive and negative poles, and the positive and negative poles are marked on the shell of these capacitors. The capacitor with a minus sign on one side is negative, and the other side is positive.

Then what caused the explosion of the capacitor? The main reason may be that the voltage and current of the capacitor are too large, and it is not ruled out that it is a quality problem. It may also be caused by the following factors:

1. The positive and negative poles are reversed;

2. The actual use voltage is higher than the nominal withstand voltage of the electrolytic capacitor;

3. The ripple in the circuit is too large;

4. The operating temperature is higher than the nominal value of the capacitor;

5. The quality of the capacitor itself;

6. After long-term use, the electrolyte is reduced, dried up, and caused by changes in capacitance parameters.

It should be noted that capacitors with positive and negative poles are electrolytic capacitors, and electrolytic capacitors have polarities. When used in electronic circuits, the anode of the electrolytic capacitor should be connected to the point of high potential in the circuit, and the cathode should be connected to the point of low potential in order to function normally. If the connection is reversed, the leakage current of the capacitor will increase sharply, and the core will heat up seriously, causing the capacitor to fail, and it may burn and explode, and damage other devices on the circuit board. Add reverse voltage to the electrolytic capacitor-"electrolyze" the insulating alumina medium and leak electricity-the leakage current generates heat and heats the electrolyte-the electrolyte vaporizes-the vapor pressure breaks through the shell (explosion).

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