Decryption of DC and AC relays
Said to relay, laymen just feel is only an on-off switch circuit, there's nothing to tangle, but when you happily go to purchase, you will find all kinds of relay is full of beautiful things in eyes, you will not know what kind of relay is suitable, you will not understand what is the difference between all kinds of relays, you even know nothing about the vocabulary for some specialised relay.
At this point the supplier will often ask you the first question, what kind of relay do you want?Maybe at this moment you do not know how to answer.Then you can describe the application scenarios in which the relay is used. If you are using a circuit that does not need to be switched on and off frequently, then Latching relays are most suitable.Otherwise, high power relays are one of the options.But when you have selected the good after the relay type, the businessman will require you to provide the load current value and the load voltage value, as well as the size of the drive coil voltage (the coil drive voltage is also called the relay coil power supply voltage) is called a relay coil, about relay drive end and the load end tend to have a lot of people to distinguish bad they should use AC relay or DC relay.This is also a lot of semi-entry relay industry electronics enthusiasts very easy to Confuse about the problem.For example: my relay input is DC, the output is AC;My relays have input AC, output DC, and so on.Faced with the problem of using AC relay or DC relay, it is necessary for us to popularize the difference between AC relay and DC relay, and then how to use it.
The most popular and simple way to judge the two is that the coil connected with DC is a DC relay, and the coil connected with 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 that the DC relay will not produce reactance when it is connected with DC current, so the coil diameter of the DC relay is relatively thin. This is mainly done to increase the internal resistance and prevent the approximate short circuit phenomenon.But when working in this way, the heat is larger, so the relay is higher and longer, mainly for good heat dissipation effect.AC relay coil is shorter, and line diameter coarser, mainly because of the coil is connected to alternating current (AC), reactance is bigger, wire diameter thick can reduce the internal resistance, reduce heat.In addition, when the alternating current crosses zero, the electromagnetic force of the coil will be reduced, the suction will not be strong, and vibration will occur. so in part on the surface of the magnet and short circuit loop, the magnetic field changes, when short circuit ring form vortex, and the electromagnetic force and magnetic field changes in the opposite direction, the hysteresis magnetic field changes, so that the electromagnet can latch better.
The scope of use of DC relays generally has two kinds of situations: applied to the protection interlock system, even in the case of AC power down, can also trigger the DC protection loop, of course, the contact must be DC system;Applied to high-power situation, some situation on the control of the electromagnetic force requirements can use DC relay, because at the same situation of “220V” but DC generated by the electromagnetic force is much larger, more favorable to the control of the main circuit.In the field of electric vehicle charging pile, we all use direct current to supply power, so we all use direct current relay.
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