Charge is the inherent property of matter. Usually, the number of positive and negative charges in an object is equal. Once an object loses or gains some electrons, it will show negative or positive charges. A regular motion of the charge produces an electric current.

1. DC: If in a circuit, the charge flows in a constant direction, this is "DC". In daily life, the current provided by the "battery" is the direct current. Batteries have polarity, which can be divided into

positive and negative electrodes.

2. AC：当电路中的电流随着方向和强度周期性地改变时，它被称为“AC”。现代发电厂生产的电能是交流电流，家庭和工业能力也是如此。

Difference between DC and AC

The alternating current varies according to the sinusoidal curve and has its frequency; the direct current does not change according to the sinusoidal curve and has no frequency change. The most intuitive difference between alternating current and direct current is that the direction of the current is unchanged; the direction of the current of direct current is unchanged at any time, but the size may change; the most special direct current is the steady current whose direction is unchanged. The so-called alternating current is the alternating flow of current, its direction is alternating change.

Skin effect: also known as skin effect, when AC passes through the conductor, the current will be concentrated on the surface of the conductor. This phenomenon is called skin effect. Why is there such a physical phenomenon? The reason is that when the conductor flows through AC, the electromotive force opposite to the current direction will be generated inside the conductor, which acts as a hindrance to the current flow. It is called back electromotive force here. The center of the conductor is larger than the flux linkage on the surface of the conductor, so the back electromotive force generated at the center of the conductor is larger than that near the surface of the conductor. If the back EMF is large, the current will flow on the surface of the conductor with smaller back EMF, while no current will pass through the center.

In summary, skin effect is only for AC, and automotive audio power supply uses 12 volts of direct current, so its conductor, that is, power line, has no skin effect. Therefore, pure oxygen-free copper is the best choice for automotive audio power supply, but copper-clad aluminum is not suitable.

Skin effect sketch of conductor

Successful Solution: 0.1 Conductor Enameled Wire Multi-Core Structure:

AC cables will use the litz lacqued in the existing specification (conductor to each other use in solated with lacquer)

One way to alleviate the skin effect is to use the so-called Leeds line (from German: Litzendraht, meaning "woven thread"). The Leeds line uses the method of winding multiple metal wires to make the electromagnetic field more evenly distributed, so that the current distribution on each wire will be more evenly distributed. With Leeds line, the frequency of significant skin effect can be increased from thousands of hertz to several megahertz. Leeds line is generally used in high frequency AC transmission, which can alleviate skin effect and proximity effect at the same time.