When replacing the power supply, how to identify the positive and negative poles of the DC output of the power adapter is usually a problem. Generally, the positive and negative poles of the power adapter are indicated on the nameplate. If there is no positive and negative identification of DC output, we can test with a multimeter.

Positive and negative representation of power adapter

1. Look at this plaque carefully. Generally, the nameplate is marked with the positive and negative poles of the DC head, as shown in the figure above

DC head identifications of different shapes are slightly different, but basically the same

If there is no mark on the nameplate, we can only do it in the following ways:

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

Turn the function switch of the multimeter to DC voltage. The black probe and the red probe are respectively connected to the two poles of the power adapter to display the positive voltage. The red probe is connected to the positive electrode and the black probe is connected 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 (this range can be gradually reduced from large to small without knowing the voltage). The black probe of the pointer multimeter is positive and the red probe is negative. The red probe of the digital multimeter is positive and the black probe is negative (the red probe is inserted into the V / Ω hole and the black probe is inserted into the com hole). Pointer multimeter: when measuring the circuit, if the pointer is positive, it proves that the wire connected with the black probe is positive and the wire connected with the red probe is negative. If the pointer is reversed, it proves that the wire connected with the black probe is negative and the wire connected with the red probe is positive. Digital multimeter: when measuring the circuit, if the surface shows a positive value, it proves that the wire connected with the red probe is positive and the wire connected with the black probe is negative. If the surface shows a negative value, the wire connected to the red probe is negative and the wire connected to the black probe is positive

3. By looking at the DC output line, if it is a 2468 flat line, we can find that the two lines of the flat line are different. One is printed and the other is striped. One side of the printed word is positive and the other side with stripes is negative. However, it is not recommended to distinguish the positive and negative poles by viewing the printed text and stripes of the DC output conductor, because some manufacturers do not connect the conductor in a conventional way. For electronic products with DC input anti connection protection, you can try. For electronic products without DC input anti connection protection, in order to avoid unnecessary loss, it is still necessary to use a multimeter for testing

Positive and negative representation of power adapter

4. Generally, round head DC heads are usually internal positive and external negative. I have also seen DC heads with external positive and internal negative, but they are very rare in the market. I still need to provide friendly tips, such as the above-mentioned method of identifying positive and negative sides by printing. For electronic products with DC input anti connection protection, you can try. For electronic products without DC input anti connection protection, in order to avoid unnecessary losses, you still need to use a multimeter for testing

To sum up, the effective method is to test the positive and negative poles of the power adapter through the power nameplate or multimeter.