How to identify the positive and negative poles of the DC output of the power adapter is usually a problem when replacing the power supply. Usually, the positive and negative poles of a power adapter are indicated on the nameplate. If there is no DC output positive and negative pole identification, we can use a multimeter for testing.

　　Positive and negative notation for power adapters

　　1. Carefully examine this plaque. In general, there are positive and negative markings on the nameplate for the DC head, as shown in the above figure

　　The identification of DC heads with different shapes may vary slightly, but they are basically the same

　　If there is no mark on the nameplate, we can only proceed through the following methods:

　　2. Use a multimeter to test the positive and negative poles

　　Turn the function switch of the multimeter to DC voltage. The black probe and the red probe are connected to the two poles of the power adapter respectively to display positive voltage. Connect the red probe to the positive electrode and the black probe to the negative electrode; If negative voltage is displayed, replace the probe to display positive voltage

　　Turn the knob to the corresponding DC voltage range (which can gradually decrease from high to low without knowing the voltage). The black probe of a pointer multimeter is the positive pole, and the red probe is the negative pole. The red probe of the digital multimeter is the positive pole, and the black probe is the negative pole (the red probe is inserted into the V/Ω hole, and the black probe is inserted into the com hole). Pointer multimeter: When measuring a circuit, if the pointer is positive, it indicates that the wire connected to the black probe is positive and the wire connected to the red probe is negative. If the pointer is reversed, it proves that the wire connected to the black probe is negative and the wire connected to the red probe is positive. Digital multimeter: When measuring the circuit, if the surface displays a positive value, it proves that the wire connected to the red probe is positive and the wire connected to the black probe is negative. If the surface displays a negative value, it indicates that the wire connected to the red probe is negative and the wire connected to the black probe is positive

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