The most common and simple way to judge the two is that the coil connected to DC is a DC relay, and the coil connected to AC is an AC relay, that is, the working power of the DC relay is DC, and the working power of the AC relay is AC. In addition, it can also be judged from the structure of the relay. Since the DC relay does not generate reactance when the DC power is applied, the coil diameter of the DC relay is relatively small. This is mainly to increase the internal resistance and prevent the phenomenon of short circuit. However, the heat generated during this operation is relatively large, so the relay is made higher and longer, mainly for good heat dissipation effect. The coil of the AC relay is short and the wire diameter is relatively thick, mainly because the reactance is relatively large after the coil is connected to the alternating current, and the thick wire diameter can reduce the internal resistance and reduce the heat generation. When the magnetic field changes, an eddy current is formed when the short-circuit ring is short-circuited, and an electromagnetic force opposite to the direction of the magnetic field change is formed, which delays the change of the magnetic field. , so that the electromagnet can be better attracted.

There are generally two situations in which DC relays are used: they are used in protection interlocking systems, and they can trigger the DC protection circuit even in the event of a power failure of the AC power supply. Of course, their contacts must also be DC systems; they are used in high-power applications. , In some occasions where there is a requirement for the electromagnetic force to be controlled, the DC relay can be used, because it is also 220V, but the electromagnetic force generated by the DC is much larger, which is more beneficial to the control of the main circuit. In the field of electric vehicle charging piles, we all use DC power to supply power, so we all use DC relays.