The positive and negative poles of a transformer's DC current can be distinguished by three differences: the shape of the markings, the color of the markings, and the deviation of the DC meter pointer:
1. The positive and negative poles of transformers with different marking shapes have clear markings for differentiation. The marking shape of the positive pole of the transformer is more prominent, while the shape of the negative pole of the transformer is flat.
2. The positive and negative poles of transformers with different colors are also distinguished by red and black. The red end of the transformer is positive, and the black end of the transformer is negative.
3. If the pointer deflection of the DC meter is different and only two outgoing lines are not clearly marked, only an ammeter can be used to determine. The two poles of the transformer's DC (connected in series with a large resistor to prevent the ammeter from burning out) are connected to both ends of the ammeter, and the positive pole of the DC power supply is on the side of the pointer deflection.
If the positive and negative poles of a regular DC motor are connected in the wrong direction, as long as the connected voltage is within the rated voltage range, it will not burn out domestically. For example, in a toy motor, the winding of a DC motor is made of copper wire. When connected to DC, the winding acts as a resistor, and we all know that resistors have no directionality, so the motor will not burn out.